Jukuri, open repository of the Natural Resources Institute Finland (Luke)               
   
 
 
All material supplied via Jukuri is protected by copyright and other intellectual property rights. 
Duplication or sale, in electronic or print form, of any part of the repository collections is prohibited. 
Making electronic or print copies of the material is permitted only for your own personal use or for 
educational purposes. For other purposes, this article may be used in accordance with the publisher’s 
terms. There may be differences between this version and the publisher’s version. You are advised to 
cite the publisher’s version. 
This is an electronic reprint of the original article.  
This reprint may differ from the original in pagination and typographic detail. 
 
Author(s): Anders Ræbild, Kesara Anamthawat-Jónsson, Ulrika Egertsdotter, Juha Immanen, 
Anna Monrad Jensen, Athina Koutouleas, Helle Jakobe Martens, Kaisa Nieminen, Jill 
Katharina Olofsson, Anna-Catharina Röper, Jarkko Salojärvi, Martina Strömvik, 
Mohammad Vatanparast, Adam Vivian-Smith 
Title: Polyploidy – A tool in adapting trees to future climate changes? A review of 
polyploidy in trees 
Year: 2024 
Version: Published version 
Copyright: The Author(s) 2024 
Rights: CC BY 4.0 
Rights url: https://creativecommons.org/licenses/by/4.0/  
 
Please cite the original version: 
Anders Ræbild, Kesara Anamthawat-Jónsson, Ulrika Egertsdotter, Juha Immanen, Anna Monrad 
Jensen, Athina Koutouleas, Helle Jakobe Martens, Kaisa Nieminen, Jill Katharina Olofsson, Anna-
Catharina Röper, Jarkko Salojärvi, Martina Strömvik, Mohammad Vatanparast, Adam Vivian-Smith, 
Polyploidy – A tool in adapting trees to future climate changes? A review of polyploidy in trees, Forest 
Ecology and Management, Volume 560, 2024, 121767, ISSN 0378-1127, 
https://doi.org/10.1016/j.foreco.2024.121767.  
Forest Ecology and Management 560 (2024) 121767
Available online 15 March 20240378-1127/© 2024 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
Polyploidy – A tool in adapting trees to future climate changes? A review of 
polyploidy in trees 
Anders Ræbild a,*,1, Kesara Anamthawat-Jonsson b, Ulrika Egertsdotter c, Juha Immanen d,e, 
Anna Monrad Jensen f, Athina Koutouleas a, Helle Jakobe Martens a, Kaisa Nieminen d,e, Jill 
Katharina Olofsson a, Anna-Catharina Roper g, Jarkko Salojarvi e, Martina Stromvik h, 
Mohammad Vatanparast i, Adam Vivian-Smith j,2 
a University of Copenhagen, Department of Geosciences and Natural Resource Management, Rolighedsvej 23, Frederiksberg DK-1958, Denmark 
b Institute of Life and Environmental Sciences, University of Iceland, Sturlugata 7, Reykjavík IS-102, Iceland 
c Swedish University of Agricultural Sciences, Dept. of Forest Genetics and Plant Physiology, PO Box 1234, Umeå SE-901 83, Sweden 
d Production Systems, Natural Resources Institute Finland (Luke), Helsinki 00790, Finland 
e Organismal and Evolutionary Biology Research Program, Faculty of Biological and Environmental Sciences, Viikki Plant Science Center, University of Helsinki, Helsinki 
00014, Finland 
f Department of Forestry and Wood Technology, Linnaeus University, Vaxjo 351 95, Sweden 
g Center for Bioresources, Danish Technological Institute, Taastrup 2630, Denmark 
h Department of Plant Science, McGill University, 21111 Lakeshore road, Sainte-Anne-de-Bellevue, QC H9X 3V9, Canada 
i Jodrell Laboratory, Royal Botanic Gardens Kew, Richmond, TW9 3AE, United Kingdom 
j Norwegian Institute of Bioeconomy Research (NIBIO), Division of Forestry and Forest Resources, P.O. Box 115, Ås N-1431, Norway   
A R T I C L E  I N F O   
Keywords: 
Adaptation 
Ecophysiology 
Fitness 
Forestry 
Tree breeding 
Whole genome duplication (WGD) 
S U M M A R Y   
Polyploidy, or genome doubling, has occurred repeatedly through plant evolution. While polyploid plants are 
used extensively in agriculture and horticulture, they have so far found limited use in forestry. Here we review 
the potentials of polyploid trees under climate change, and investigate if there is support for increased use. We 
find that polyploid trees like other plants have consistent increases in cell sizes compared to diploids, and that 
leaf-area based rates of photosynthesis tend to increase with increasing levels of ploidy. While no particular trend 
could be discerned in terms of biomass between trees of different ploidy levels, physiology is affected by poly-
ploidization and several studies point towards a high potential for polyploid trees to adapt to drought stress. The 
ploidy level of most tree species is unknown, and analysis of geographical patterns in frequencies of polyploid 
trees are inconclusive. Artificial polyploid trees are often created by colchicine and in a few cases these have been 
successfully applied in forestry, but the effects of induced polyploidization in many economically important tree 
species remains untested. Polyploids would also be increasingly useful in tree breeding programs, to create 
synthetic hybrids or sterile triploids that could control unwanted spreading of germplasm in nature. In 
conclusion, this review suggests that polyploid trees may be superior under climate change in some cases, but 
that the potential of polyploids is not yet fully known and should be evaluated on a case-to-case basis for different 
tree species.   
1. Introduction 
Forest ecosystems contribute significantly to the diversity and pro-
duction of the Earth’s biomass (Bar-On et al., 2018). While there is 
concern for the future health of forests due to climate change (e.g., 
Hartmann et al. 2022), reforestation could have a significant impact by 
regaining control of the terrestrial carbon cycle, and help counteract the 
effects of climate change. A simple but so far unexplored method to 
enhance the robustness and productivity of many forest tree species 
could be polyploidy, or genome duplications. Since the 1930’s, natural 
* Corresponding author. 
E-mail address: are@ign.ku.dk (A. Ræbild).   
1 ORCID 0000-0002-8793-5663  
2 ORCID 0000-0002-8074-7950 
Contents lists available at ScienceDirect 
Forest Ecology and Management 
journal homepage: www.elsevier.com/locate/foreco 
https://doi.org/10.1016/j.foreco.2024.121767 
Received 20 December 2023; Received in revised form 9 February 2024; Accepted 12 February 2024   
Forest Ecology and Management 560 (2024) 121767
2
polyploids, induced mutations and polyploidization by chemicals and 
irradiation have been used for general plant improvement (Darrow, 
1950; Sigurbjornsson and Lachance, 1987), shaping agriculture and 
leading farmers into the ’Green revolution’ (Hedden, 2003; Jung and 
Till, 2021). Although many examples of polyploidization in agriculture 
and horticulture have led to significant improvement in productivity 
and trait performance (Motosugi et al., 2002, Wu et al., 2012), its 
application in forestry has been limited. However, there are many po-
tential advantages of utilizing polyploids in forestry including increased 
resistance to abiotic stresses (e.g., Maherali et al., 2009; Tossi et al., 
2022), superior performance under elevated CO2, and changed wood 
properties (da Silva Souza et al., 2021). 
Polyploids often have altered plant development compared to their 
diploid relatives. Key phenotypic differences, such as larger cell sizes for 
higher ploidy levels, tend to hold in ploidal series across plant orders 
including bryophyte, fern, gymnosperm and angiosperm lineages 
(Henry et al., 2014; Scholes and Paige, 2015; Alix et al., 2017; Karlin and 
Smouse, 2017; Smarda et al., 2018; Wilson et al., 2021; Patel et al., 
2021). Trees, however, differ from non-woody plants in having sec-
ondary growth and extended xylem. This makes trees tall and wide, 
giving them an edge in ecosystems when competing for light. In addi-
tion, trees have longer generation times and life spans than herbs and 
forbs, which may affect their potential for adaptation to rapid envi-
ronmental change. Given the hypothesized evolutionary advantage of 
polyploids during previous environmental upheavals (Van de Peer et al., 
2017), polyploids may have an adaptive advantage in their response to 
the challenges of climate change (Lomax et al., 2014; Faizullah et al., 
2021; Ebadi et al., 2023). 
There is extensive research on the evolutionary role of poly-
ploidization and whole genome duplications (WGD) in key terrestrial 
plant radiation events, particularly for tracheophytes (Soltis et al., 2015; 
Clark and Donoghue, 2018). Even as this review was concluding, Bures 
et al., (2024) explored the relationships between bioclimatic environ-
ment, genome size, polyploidy and growth form in angiosperms, and 
concluded that woody angiosperms were less frequently polyploid and 
that genome size regulation may operate differently. There is, however, 
Box 1 
Glossary/list of terms. 
Accessory or cloud genes: Genes that are found in some, but not all, species or individuals in a taxon or taxonomic group. These genes are seen 
as non-essential, however, they bring uniqueness and are often advantageous to the bearer (e.g. disease resistance genes, stress tolerance, 
flowering time). 
Allele-dosage/gene-dosage: The variable amount of gene product that is the result of multiple copies of an allele, or gene, on homologous and 
homeologous chromosomes. 
Allopolyploid: A polyploid formed from the merging of gametes from different species or highly diverged populations. 
Aneuploidy: State of organisms and cells with an unbalanced set of chromosomes with respect to their parents. Aneuploid organisms may have 
chromosomal instability (chromosome breakage causing gene loss) or have an abnormal number of chromosomes, such as one extra or one fewer 
chromosomes than expected. 
Apomixis: Is the process of clonal reproduction via asexual seeds, and is often found associated with natural polyploids and ploidal variation. 
While apomixis often has complex evolutionary origins, and often low frequency amongst plants, the molecular basis for naturally occurring and 
synthetic modes of apomixis is now well understood, and may provide significant benefits to agriculture or forestry due to the fixation of hybrid 
vigor. 
Autopolyploid: A polyploid formed by whole genome duplication (WGD) often caused by merging of unreduced gametes from individuals of 
the same species. 
Copy number variation: The variation in the number of genes for discrete loci caused by tandem duplication, or from the number of gene loci 
occurring in polyploids. 
Core genes: Set of genes that are shared by all individuals or species in a taxon or taxonomic group. 
Diploid: Cells of an organism that have two complete sets of chromosomes, one set from each parent. Chromosomes are represented as ho-
mologous pairs in diploid organisms, and the diploid state is typical of somatic cells. 
Genomics: The study of the structure, function, and evolution of the total genetic and/or epigenetic sequence information (the genome) of 
organisms. 
Haploid: Cells of an organism that have one complete set of chromosomes, typically gamete cells. 
Heterosis: Non-additive inheritance of phenotypic traits as observed from hybridization of two different parental lines, species or genera. 
Hybrid vigor is a highly sought after effect of heterosis. 
Homeologous chromosomes: matching chromosomes in the genomes of different species. Previous to speciation, these were homologous 
chromosomes. 
Homologous chromosomes: the matching chromosomes in two sets of chromosomes in diploids, or in more than two sets of chromosomes in 
autopolyploids. 
Neo-functionalization: The development of a new function of a gene copy (co-option) following duplication. 
Neopolyploid: A newly formed polyploid lineage. Neopolyploids can be further defined as neoallopolyploids and neoautopolyploids. 
Polyploid: Cells of an organism that have more than two complete sets of chromosomes. Depending on the number of chromosome sets, they are 
referred to as triploid (three sets), tetraploid (four sets), pentaploid (five sets) etc. 
Sub-functionalization: Gene copy expression patterns associated with different or novel time or tissue types following gene duplication. 
Sub-genome: The set of chromosomes derived from distinct progenitor species.  
A. Ræbild et al.                                                                                                                                                                                                                                 
Forest Ecology and Management 560 (2024) 121767
3
a continued lack of understanding of the specific role of polyploidy for 
forest tree species during evolution. This review therefore examines if 
the benefits of altered plant development that are often seen in polyploid 
crop plants, also hold for polyploid forest trees. We summarize the 
contemporary research on natural and artificial polyploid forest trees to 
investigate whether there is evidence for the superior performance of 
polyploid trees under climate change conditions, and if polyploidy can 
be used as a tool in forestry and breeding programs to enhance the 
resilience of our forests. 
2. Formation of polyploids and molecular effects of 
polyploidization 
Polyploidization is an integral part of plant evolution, and most, if 
not all, plant genomes have undergone polyploidization at some stage 
(Van de Peer et al., 2017; Simonin and Roddy, 2018). While whole 
genome duplications within a species, autopolyploidization, can 
happen, allopolyploids are thought to be more common. Allopolyploids 
are established from hybridization between divergent lineages followed 
by genome duplications (Box 1, Fig. 1; Otto and Whitton, 2000; Mallet, 
2007). Early research on (allo)polyploids provoked a hypothesis on a 
“Genomic shock” (McClintock, 1984) in the neo-(allo)polyploid species, 
possibly driven by transposable elements, with extensive genome-wide 
changes. In contrast, recent research has found a peaceful coexistence 
of the sub-genomes, with the regulation of different processes divided 
between them (e.g., Bird et al., 2018; Duan et al., 2023). Over time 
polyploid genomes tend to become re-diploidized (Ramsey & Schemske, 
2002; Conant et al., 2014). Following the initial polyploidization event, 
the novel lineage undergoes genome fragmentation (Zhu et al., 2019), 
either with equal gene loss in both sub-genomes (Liang and Schnable, 
2018), or with one sub-genome losing genes at a more rapid rate while 
the other becomes dominant, as in Gossypium (Chen et al., 2020; Con-
over and Wendel, 2022). This process can also result in novel genetic 
variation in the form of neofunctionalization or sub-functionalization, 
where multiple gene copies provide the opportunity for further 
specialization (Liang and Schnable, 2018; Van de Peer et al., 2021). Past 
ancestral history of polyploidization may also have a persistent influ-
ence on gene expression and genomic dominance (Yoo et al., 2013; 
Liang and Schnable, 2018). 
While the molecular and genomic effects of polyploidization are well 
studied in particular crop plants, little data has so far been obtained for 
tree species due to their long generation times and thus difficulties in 
multi-generational studies. The molecular effect of hybridization, and 
allopolyploidization, depends on the genetic similarities between the 
diploid progenitors, their divergence time and differences in their gene 
regulation, with perhaps the most extensive effects (i.e. genomic shock) 
resulting from more diverged progenitors. For example, while the sub- 
genomes of allopolyploids have a conserved order (synteny) for the 
majority of their core genes, each sub-genome can also contain a unique 
set of genes (accessory or cloud genes) that may confer stress or disease 
resistance to newly formed polyploids (neo-polyploids) (Chen et al., 
2020). Neo-polyploids, in particular neo-allopolyploids, may thus have 
important advantages over their diploid progenitors. Hybrids and 
neo-allopolyploids may also display heterosis and thus outperform their 
parental lineages. The genomic underpinnings of heterosis, however, are 
not very well understood, but are suggested to be controlled by a com-
plex set of molecular processes including sub-genome dominance 
(Carlson et al., 2022; Carlson and Smart, 2022; Yu et al., 2021) and 
haplotypic divergence, changes in allele-dosage and novel regulatory 
interactions affecting gene expression networks (Hu et al., 2022). Ex-
amples of the latter are found in Salix L. (Carlson et al., 2022; Carlson 
and Smart, 2022), Populus L. (Liqin et al., 2019), and Quercus L. (2 n ˆ
36; Butorina, 1993; Dzialuk et al., 2007; Johnsson, 1946; Lefort et al., 
1998; Lefort et al., 2000; Naujoks et al., 1995). The fast growth of these 
trees could be derived from a combination of copy number variation and 
heterosis. 
3. Changes in anatomy and morphology of polyploid plants 
There is a tendency across plant species that cell size correlates with 
genome size (Cavalier-Smith, 2005; Hodgson et al., 2010; Robinson 
et al., 2018), although this may be cell type dependent (Katagiri et al., 
2016). Increased cell size affects a great number of key physiological 
processes in plants such as water holding capacity, and transport of 
gasses and solutes (Trojak-Goluch et al., 2021). 
Since polyploid plants tend to have larger stomata that are posi-
tioned further apart compared to their diploid relatives (e.g., Smarda 
et al., 2023, Fig. 2), this trait can be used to identify polyploids. This is 
also true for tree species across a large phylogenetic spectrum (Fig. 3a, 
b). Increases in stomatal cell size may be accompanied by increases in 
the size of other cell types, including epidermal cells and mesophyll 
parenchyma, resulting in thicker leaves in polyploids (Chen et al., 2021). 
This means that both the amount of dry mass and the water mass per leaf 
area may increase in polyploids compared to diploids and has been re-
ported in several woody genera (Barcelo-Anguiano et al., 2021; Li et al., 
2009; Romero-Aranda et al., 1997; Zhang et al., 2019a). Larger cell sizes 
in polyploids do not necessarily lead to a larger surface area of leaves, as 
there may be a correspondingly lower number of cells in the leaves 
(Robinson et al., 2018). Data from woody species are contrasting, with 
some studies showing that polyploids have shorter, but thicker leaves 
than their parental diploids (Xue et al., 2017), some showing no increase 
in leaf area (Diallo et al., 2016; Fernando et al., 2019), and some 
showing larger leaf areas in polyploids (Chen et al., 2021; Hao et al., 
2013; Wang et al., 2017b). The number of studies is too limited to relate 
these differences to phylogeny or habitats of the species. 
Sizes and numbers of organelles are also affected by the level of 
ploidy. Larger stomata are associated with an approximate doubling of 
chloroplast numbers in guard cells in tetraploids compared to diploids 
(Beck et al., 2003; Tang et al., 2010; Shi et al., 2015; Abdolinejad and 
Shekafandeh, 2022), and chloroplast sizes were approximately double in 
tetraploid Mangifera indica L. compared to diploids of the same species 
(Barcelo-Anguiano et al., 2021). 
There are relatively few studies that go beyond leaf anatomy, but 
they seem to indicate that polyploids have larger cell sizes in other parts 
of the plant. For example, tetraploid Citrus genotypes have been shown 
to have thicker roots than diploids (Syvertsen et al., 2000; Ruiz et al., 
2016a). Polyploids had larger structures in the hydraulic systems such as 
longer and wider vessel elements and sieve tube elements (Hao et al., 
2013; (Barcelo-Anguiano et al., 2021; De Baerdemaeker et al., 2018)). In 
species of Betula L. from China vessel diameters were larger in polyploids 
compared to diploids, although intervessel pits had smaller dimensions 
in polyploids, resulting in a larger resistance to cavitation compared to 
diploids (Zhang et al., 2017). 
Fig. 1. Natural formation of polyploids from diploids (2x) to triploids (3x), 
tetraploids (4x) and hexaploids (6x). The figure illustrates autopolyploids from 
whole genome duplication, and allopolyploids via inter-specific hybridization 
and back-crossing from e.g. two different species. Modified from Yirga (2021). 
A. Ræbild et al.                                                                                                                                                                                                                                 
Forest Ecology and Management 560 (2024) 121767
4
Floral morphology and anatomy of trees are also affected by ploidy 
level, with polyploids showing overall larger morphologies than diploids 
(Borges et al., 2012; Fernando et al., 2019; Oliveira et al., 2022). This 
includes pollen (Shi et al., 2015, Mendes-Rodrigues et al., 2019) and 
polyads as well as stigma cups (Diallo et al., 2023). It is generally sug-
gested that such differences could act as a reproductive barrier for gene 
flow between ploidy levels, thus contributing to reproductive isolation. 
Although the available evidence suggests larger cell sizes throughout 
all organs of the polyploid plants compared to diploids, there is insuf-
ficient data to verify whether all cell types are affected to the same de-
gree by ploidy. As a larger cell size may influence physiological 
performance and wood quality, there is a need for additional studies of 
the anatomy of polyploid trees at several levels of the plant. 
4. Physiology of polyploid trees 
4.1. Photosynthesis in polyploid trees 
It has been hypothesized that smaller genomes are advantageous 
under low CO2 conditions because this leads to smaller leaf structures 
and thus faster diffusion of CO2 to the sites of photosynthetic assimila-
tion (reviewed by Faizullah et al., 2021). This theory is corroborated by 
reports of extensive reduction in genome size of angiosperms during the 
Cretaceous, which allowed for reductions in cell sizes, higher intracel-
lular surface areas and more efficient CO2 diffusion into photosynthetic 
mesophyll cells, in turn maximizing primary productivity (Simonin and 
Roddy, 2018; Theroux-Rancourt et al., 2021). Polyploidization in trees 
Fig. 2. The sizes of stomata are positively correlated to genome size in Acacia senegal. a) Tetraploid, stomata length 22.2  1.4 µm. b. Diploid, stomata length 16.8 
1.2 µm. nˆ 10. Barˆ 20 µm. 
Fig. 3. Anatomical and physiological traits in tree species with varying ploidy levels. a) Stomatal density. b) Stomatal length. c) Operating stomatal conductance, Gs. 
d) Net photosynthesis, Pn. Inserted P-values indicate tests of effects of ploidy level from a mixed model analysis with the ploidy level as a fixed factor and species/ 
variety as a random factor. Data and references are available from Table S1. 
A. Ræbild et al.                                                                                                                                                                                                                                 
Forest Ecology and Management 560 (2024) 121767
5
may, however, have been most relevant during the Devonian and part of 
the Mesozoic, known for high humidity and atmospheric CO2 concen-
trations (Veselý et al., 2020). Under these conditions, larger (slower) 
stomata would not have been detrimental to the overall CO2:H2O status 
of the plant, as they could remain open for longer periods without 
risking excessive water loss (Veselý et al., 2020). However, with the 
climatic shifts occurring during the Carboniferous to Permian periods 
and from the mid-Cenozoic onwards, the cooler and drier environments 
(characterized by low atmospheric CO2 concentrations) may have 
incurred a selective pressure on stomatal downsizing to optimize 
intracellular CO2:H2O (Veselý et al., 2020; Wang et al., 2021). Yet, the 
only study to test this hypothesis in trees found that increases in net 
photosynthesis under elevated CO2 were similar in tetraploid and 
diploid genotypes of the genus Citrus L., indicating no superiority of 
tetraploids in this context (Syvertsen et al., 2000). 
Although very little is known about how diffusion inside the leaf is 
affected by changes in ploidy levels, the ploidy-induced, leaf anatomical 
changes may modify the diffusion pathway for CO2 and water vapor. 
These leaf traits can potentially alter conductance and possibly even the 
CO2:H2O ratio. For example, larger leaves in polyploids may have 
greater boundary layer resistances than smaller leaves of lower cyto-
types (Nobel, 1999). Stomatal conductance (gs) in polyploids is reduced 
by a generally lower number of stomata per leaf area, but on the other 
hand could be increased by their larger pore sizes compared to diploids 
(Faizullah et al., 2021, Smarda et al., 2023). Our analysis of differences 
in gs among ploidy levels for a range of tree species shows no general 
tendencies (Fig. 3c). Thus, ploidy-induced anatomical changes to the 
stomatal apparatus may affect conductance and its regulation capacity. 
Although not directly testing for the effect of ploidy, intracellular 
diffusion of gasses and water have been shown to be slower in large 
mesophyll cells and enlarged chloroplasts compared to smaller and more 
densely shaped anatomies (Xiong et al., 2017; Theroux-Rancourt et al., 
2021). In Acacia senegal (L.) Willd. and Populus tremuloides Michx., 
carbon isotopic composition suggested that water use efficiency is 
greater in polyploids than in diploids, as would be expected when the 
diffusive pathway for CO2 is longer (Greer et al., 2018; Diatta et al., 
2022). 
The larger dimensions of leaves, cells and organelles in polyploids 
are mostly associated with increases in rates of net photosynthesis (e.g., 
Xue et al., 2017; García-García et al., 2020; Chen et al., 2021). A limi-
tation of several studies is that they are based on one or two genotypes of 
each cytotype, restricting conclusions to the specific genotypes involved. 
However, our analysis across different species and genotypes indicates 
that photosynthesis (when expressed on a leaf area basis) is higher with 
increasing levels of ploidy (Fig. 3d). Still, Populus triploids had faster 
rates of photosynthesis and growth compared to diploids and tetra-
ploids, suggesting that there is not always a direct link between genome 
size and physiology (Zhao et al., 2015; Zhang et al., 2019a). 
There is a scarcity of studies examining the scaling effects, which 
come with larger genome sizes and how this interacts with plant CO2 
uptake and water loss (Wang et al., 2021). The ‘large genome constraint 
hypothesis’ was tested across phylogenies in the context of photosyn-
thetic performance, demonstrating that photosynthetic rates (per leaf 
weight) were lower with increased genome size in gymnosperms, but 
not in angiosperms (Knight et al.,2005; Beaulieu et al., 2008). We are 
not aware of studies investigating this dynamic in polyploid trees. Since 
thick leaves may have high rates of photosynthesis (when expressed on a 
per-area basis) and low rates (when expressed per dry weight), a pros-
pect lies in the possibility that methods used to estimate photosynthesis 
may lead to opposite conclusions regarding photosynthetic capacity in 
polyploid trees. 
4.2. Physiological variation of polyploid trees under drought 
There is a limited number of studies on the stress responses of 
polyploid trees, mainly focusing on horticultural species. However, 
examples of polyploid superiority (compared to diploids of the same 
species) include conditions of chilling stress, bacterial disease and 
salinity (Ruiz et al., 2016a,b; Luo et al., 2017; Zhao et al., 2017; Sivager 
et al., 2019, 2021; Lourkisti et al., 2020). Here we focus on climate 
change where drought has been identified as a major challenge. 
Stress trials have shown evidence of drought resilience in polyploid 
trees (Diallo et al., 2016; Lourkisti et al., 2021a,b). The underlying 
biochemical and signaling mechanisms which cause greater drought 
tolerance in polyploids are not well understood. However, it has been 
shown that the important abscisic acid (ABA) signaling pathways are 
affected (Allario et al., 2013; Rao et al., 2020). In addition, osmotic 
adjustment and other water-saving physiological traits (in polyploid 
trees) could explain the apparent drought tolerance compared to diploid 
individuals (as is the case for Betula - Li et al., 1996; Malus - Zhang et al. 
2015; de Baerdemaeker et al., 2018; Citrus - (Lourkisti et al., 2021a,b; 
Lourkisti et al., 2022; and Mangifera indica - Perera-Castro et al., 2023). 
Significantly higher concentrations of soluble sugars, proline, and 
glycine betaine were found in tetraploid genotypes compared with 
diploid genotypes of young Ficus carica L. (Abdolinejad and Shek-
afandeh, 2022). Accumulation of these compounds no doubt plays a role 
in plant cell-water balance. 
Changed xylem anatomy in polyploids also appears to lead to 
changed hydraulic properties (Barcelo-Anguiano et al., 2021; De Baer-
demaeker et al., 2018; Hao et al., 2013). Root hydraulic conductivity of 
tetraploids was found to be smaller compared to diploids in both Citrus 
ssp. and Salix viminalis L. (Dudits et al., 2016; Ruiz et al., 2016a,b), but in 
other Citrus genotypes, the hydraulic conductivity was not affected by 
the level of ploidy (Syvertsen et al., 2000). In a modeling approach 
where polyploids were assumed to have larger vessel and sieve tube 
sizes, polyploids showed increased hydraulic conductance compared 
with diploids (Barcelo-Anguiano et al., 2021). Additionally, De Baer-
demaeker et al. (2018) found higher relative water content and lower 
stress response in autotetraploid under in-vitro drought conditions linked 
to gene expression levels for aquaporin controlling genes (MdPIP1;1 and 
MdTIP1;1). However, the hydraulic conductance of the shrub Atriplex 
canescens (Pursh) Nutt. decreased with increasing ploidy despite larger 
vessel sizes (Hao et al., 2013). This suggests that hydraulic conductance 
cannot be evaluated based on vessel anatomy alone. Importantly, Hao 
et al. (2013) found that plants with higher ploidy had smaller loss of 
hydraulic conductivity under tension, suggesting that polyploids would 
be more resistant to severe drought. 
Upon water deficit conditions, vascular plants initiate systemic 
intercellular communication involving the phytohormones ABA and 
cytokinins, which eventually accumulate in the leaves and cause sto-
matal closure (Verslues, 2016; Takahashi et al., 2020). This reduces 
additional water shortages, which could occur via leaf transpiration. The 
ABA in tetraploid Prunus salicina Lindl. was found to accumulate later 
than in the diploid leaves under water-stress (Pustovoitova et al., 1996), 
attributed to the larger cells and organelles of the polyploid, thus 
imposing a biophysical constraint on the signaling of ABA. However, the 
final ABA content and cytokinin activity in the tetraploid leaves were 
found to exceed that in the diploid leaves. Although the transpiration 
rate decreased more rapidly in tetraploids under drought conditions it 
recovered more quickly after subsequent rehydration episodes 
compared to diploid plants, suggesting an acclimation response to the 
drought stress exhibited solely by the tetraploids after repeated drought 
exposure (Pustovoitova et al., 1996). 
Collectively, these controlled and semi-controlled drought experi-
ments in growth chambers and greenhouses suggest the superior per-
formance of polyploid trees under drought. Unfortunately, this has 
rarely been tested in field trials. Studies under controlled conditions and 
in the field of diploid and triploid Populus tremuloides have come to 
opposite conclusions, pointing to an overall lower resilience to drought 
in triploids under field conditions (Greer et al., 2018; Blonder et al., 
2021; Eisenring et al., 2023). Despite greater instantaneous water use 
efficiency, triploid P. tremuloides in the field showed lower resilience to 
A. Ræbild et al.                                                                                                                                                                                                                                 
Forest Ecology and Management 560 (2024) 121767
6
climate-induced stress and had higher mortality than diploids (Blonder 
et al., 2021). Studies such as these include extraneous variables but are 
better indicative of the eco-physiology of polyploid trees under natural 
environments compared to laboratory assessments. 
4.3. Regulation of growth in polyploid trees 
The “gigantism” exhibited by the autotetraploids can be associated 
with altered signal transduction of indoleacetate (IAA) and upregulation 
of six genes involved in the biosynthesis and signal transduction of 
ethylene (Mu et al., 2012b). The autotetraploid Betula platyphylla 
Sukaczev has a unique phenotype compared to diploids of the same 
species, with a more dense stature characterized by increases in 
breast-height diameter, volume, leaf and catkin sizes. Also, certain 
triploid Betula lineages were found to be superior in base diameter and 
height to base diameter ratio when compared to the diploid lineages (Mu 
et al., 2012a). Both IAA and ethylene have key roles in regulating plant 
growth and cell enlargement, and thus their altered functions and 
expression in the autotetraploid could explain the altered phenotype 
(Mu et al., 2012b). A similar increase in biomass was reported for au-
totetraploids of the fast-growing deciduous species of Paulownia elongata 
S.Y.Hu (Zhi-qing, 2006). Several genes were shown to co-regulate 
biomass production and are thus presented as ideal targets in breeding 
programs (Cao et al., 2020). Amongst others, genes involved in 
improved chloroplast formation, and thus improved photoassimilation, 
were put forward to be most likely responsible for the increased biomass 
in the tetraploid (Cao et al., 2020). 
There are, however, contrasting results between studies and species 
concerning the regulation of growth. Some researchers suggest that 
plant growth is reduced with increasing ploidy level due to increased 
numbers of chromosomes, which may lead to slow mitotic division, and 
lower overall growth (Ramsey and Schemske, 2002). In particular, 
meiotic and mitotic rates have been hypothesized to be slower in poly-
ploids (compared to diploids) due to more time needed for the 
Fig. 4. a) Heat map presenting the distribution of tree species per country based on the GlobalTreeSearch database (Beech et al., 2017); b) Polyploid tree species 
distribution heat map generated based on the dataset from Rice et al. (2019). Note: areas with low frequencies may be under-represented in this database. 
A. Ræbild et al.                                                                                                                                                                                                                                 
Forest Ecology and Management 560 (2024) 121767
7
replication of the genome prior to cell division (Tate et al., 2005). 
Another possible explanation for slow cell division in polyploids is 
spatial constraints (Corneillie et al., 2019), particularly concerning the 
organization of chromosomes during metaphase alignment and spindle 
attachment, which are more likely to be perturbed or delayed due to the 
high number of chromosomes in the nucleus of polyploid species 
(Comai, 2005). Slow ontogeny has also been reported in tetraploid po-
tato (Solanum tuberosum L.) (Tamayo-Ordo~nez et al., 2016). However, 
these delays in development could be mitigated by faster and early 
germination by larger seeds, which is a common characteristic of poly-
ploid plants (Tate et al., 2005; Selvi & Vivona, 2022). Growth in poly-
ploid trees may also be limited by the increasing costs of larger cell size 
structures, for example pollen tube growth (Williams & Oliveira, 2020). 
This feature was observed in both Betula and Handroanthus species. 
There may also be relevant interactions between genetic background 
and ploidy level which may be overlooked, if single genotypes are 
examined. Genotype-ploidy dependent interactions have been demon-
strated in Zea mays L., where the morphological response to ploidy 
change was genotype specific and shown to vary along inbred lines 
(Riddle et al., 2006). 
Given the lack of consistency between studies, there is still a need to 
examine the role which genome size plays in the regulation of growth in 
trees. Until this is understood, the potential use of polyploid trees in 
forestry must be studied individually for key species and genotypes. 
5. Natural occurrence of polyploidy in trees 
Trees are vital for global plant biodiversity, representing about 
60,000 species and nearly 20% of seed plants (Beech et al., 2017). The 
highest diversity of tree species is found in the tropical regions of South 
America, Asia, and Africa (Fig. 4a). Estimates suggest that 30–70% of 
angiosperms and approximately 10% of gymnosperms are polyploids 
(Wood et al., 2009; Rastogi and Ohri, 2020; Ohri, 2021). In general, 
polyploid frequency tends to increase with distance from the equator, 
influenced by climate, particularly temperature (Ramsey and Schemske, 
1998; Rice et al., 2019; Bures et al., 2024). In contrast, polyploid tree 
species appear to be more common in tropical regions (Fig. 4b). This 
heatmap of distribution is likely biased, however, as it is based only on a 
few thousand ploidy-known tree species worldwide. The exact number 
of polyploid tree species and the extent of natural occurrence of poly-
ploid tree species remains unknown. 
In gymnosperms, polyploids are rare and mainly found in Ephedrales 
and Cupressales, with high incidences in Ephedra L. (76%) and Juniperus 
L. (22%) (Ohri, 2021). In addition, there are stable polyploid cultivated 
forms of Ginkgo biloba L. (Smarda et al., 2018), and the hexaploid 
Sequoia sempervirens (D.Don) Endl. is one of the most valuable timber 
species in the forest industry in Northern America and New Zealand 
(Meason et al., 2016). In angiosperms, frequencies of polyploids appear 
to be variable among taxonomic clades (Fig. S1, S2). At the family level, 
Fabaceae, Asteraceae, Malvaceae and Rosaceae have the highest 
numbers of polyploid woody plant genera (Fig. S1a). Forest tree genera 
with a relatively high proportion of polyploids, such as Alnus Mill., Tilia 
L., Sorbus L., and Betula, are those having their natural distribution range 
in the northern temperate region (Fig. S1b,c). The genus Sorbus (rowan) 
comprises some 150 species mostly in the northern temperate regions. 
These include mostly out-crossing diploids (2 nˆ2xˆ34), apomictic 
triploids (2 nˆ3xˆ51) and tetraploid (2 nˆ4xˆ68) species 
(Hajrudinovic et al., 2015; Kaplan et al., 2019; McAllister, 2005). Most 
of these polyploid species have deficient fertility, having originated from 
interspecific hybridization, and then followed by WGD in the case of 
tetraploidy. Therefore apomixis, which is defined as the clonal repro-
duction via asexual seed (Underwood and Mercier, 2022; see Box 1), 
provides a mechanistic advantage that allows the continued survival of 
triploid individuals within this genus. Since there is still relatively little 
genomic research on tropical tree species, the proportion of polyploids is 
largely unknown. This is also hampered by the immense species 
diversity; for example the Dipterocarpaceae, a tropical tree family that is 
the foundation species in many forest ecotypes in South East Asia, and is 
the major source of high quality hard wood in timber trade in the region, 
consists of around 700 species (Appanah and Turnbull, 1998). 
Polyploidy can be detected by direct or indirect methods. Indirect 
methods rely on the analyses of morphological traits such as larger 
stomata in lower density and/or a higher number of chloroplasts per 
guard cell (see above). In contrast, direct methods measure the nuclear 
genome size by flow cytometry, which measures DNA content per cell, 
and/or chromosome counting, both of which are more accurate than 
indirect methods. In particular, chromosome numbers obtained visually 
from microscopic images provide further information, such as karyo-
typic variation and genome composition in polyploids, and offer deeper 
insights into chromosome evolution especially when using molecular 
cytogenetic techniques. 
Estimating the number and distribution of polyploid tree species 
globally is challenging due to the lack of chromosome counts for most 
tree species. Globally, chromosome records are available for less than 
20% of angiosperms and are biased toward specific clades (Rice et al., 
2015). Unfortunately, only 10% of all tree species have available chro-
mosome numbers in the Chromosome Counts Database (data retrieved 1 
April 2023). Advanced techniques like estimating genome size with flow 
cytometry are used, but actual genome size data is available for only a 
fraction of plant species (Pellicer et al., 2018). To increase our knowl-
edge, prioritizing affordable chromosome counting methods is crucial, 
especially in tropical and subtropical regions where tree species di-
versity is concentrated. 
There are, however, some genera, including birch (Betula), that have 
been extensively studied. Betula comprises 40–60 tree/shrub species 
distributed from the sub-tropical and temperate to the arctic regions of 
the Northern Hemisphere (eFlora, 2023, Furlow, 2023). Hybridization 
among Betula species is frequent (Ashburner and McAllister, 2013; 
Johnsson, 1945; Walters, 1964) and hybrids are often found in the 
overlapping area of natural distributions. In contrast to oak (Quercus), 
beech (Fagus L.) and chestnut (Castanea Mill.) that are ploidy-stable at 
the genus level (mostly diploid 2 nˆ2xˆ24; Chokchaichamnankit et al., 
2008; Rice et al., 2019), Betula is an example of a ploidy-variable genus 
(Fig. S2, Table S2). Among Betula species, the ploidy levels range from 
diploid (2x) to dodecaploids (12x), with the tetraploid number 
2 nˆ4xˆ56 being the most common (Rice et al., 2015; Wang et al., 
2016; eFlora, 2023). Overall, there are more polyploid (56%) than 
diploid (44%) species, and in terms of abundance and geographic range, 
polyploid species are more common in Eurasia than in North America 
(42 vs. 15 species; Table S2). Interestingly, the proportion of polyploid 
Betula species does not increase at higher latitudes as is generally 
observed among other flowering plants. Several arctic and alpine species 
are diploid, such as the dwarf birches B. nana L. and B. glandulosa Michx. 
(de Groot et al., 1997) and Alaskan tree birch B. neoalaskana Sarg. 
(Furlow, 2023), whereas a few sub-tropical Asiatic species are polyploid, 
such as B. alnoides Buch.-Ham. ex D.Don and B. cylindrostachya Wall. 
(both tetraploids with 2 nˆ4xˆ56, eFlora, 2023). In addition, the ratio 
of diploid to polyploid Betula species is the same in both mountain 
forests at high altitudes and in the lowland areas (Table S2). Thus, 
diploids and polyploids of Betula are symmetrically distributed. In the 
case of Alder (Alnus species), most polyploid species are distributed in 
the East Asia and Mediterranean region, whereas European and Amer-
ican species are predominantly diploid (Vít et al., 2017). Recently 
discovered tetraploid populations of A. glutinosa (L.) Gaertn. in Morocco 
(Lepais et al., 2013) and the newly described tetraploid species 
A. lusitanica Vít, Douda & Mandak and A. rohlenae Vít, Douda & Mandak 
in Southern Europe and North Africa (Vít et al., 2017) open possibilities 
to test the performance and potential use of these taxa in forestry. 
6. Producing artificial polyploid trees for forestry 
Different methods to obtain chromosome set doubling have been 
A. Ræbild et al.                                                                                                                                                                                                                                 
Forest Ecology and Management 560 (2024) 121767
8
applied to in vitro cultures as a fast-track method of obtaining artificial 
polyploids of commercially interesting tree species like Eucalyptus L′Her. 
(Silva et al., 2019), and also to restore fertility in newly synthesized 
alloploids (Sattler et al., 2016). Artificial polyploids in trees have been 
most frequently induced by the antimitotic agent colchicine, which 
mechanistically disrupts the cell cycle (Touchell et al., 2020). Different 
tree parts can be treated with colchicine to induce chromosome 
doubling, the first step in polyploidization. However, most treatments 
target different types of in vitro cultures of shoot tissues, leaf material 
and established meristematic tissues. Mature leaf blades of Populus x 
hopeiensis Hu & H.F.Chow were treated with colchicine and the induced 
tetraploid plants mostly came from around vein tissues (Wu et al., 2020). 
Furthermore, octoploid plants were derived from the tetraploid plants, 
and the phenotypic consequences of gene dosage effects were evaluated 
in the ploidy series of 2x, 4x and 8x plants (Wu et al., 2022). Allohex-
aploids were also generated in another effort to investigate the perfor-
mance of economic traits in Populus with higher ploidy levels (Liu et al., 
2018). In Eucalyptus polybractea R.T.Baker, nodal shoot cultures were 
successfully treated with colchicine to induce formation of thicker 
leaves with larger oil glands (Fernando et al., 2019). Seeds were steril-
ized and treated with colchicine to induce chromosome doubling in 
Acacia dealbata Link and A. mangium Willd. (Blakesley et al., 2002). The 
tetraploid plants were subsequently used for breeding to generate sterile 
triploid trees. Colchicine treatment of seeds was also successful for 
inducing tetraploids in Platanus x acerifolia (Aiton) Willd. (Liu et al., 
2007). In horticultural tree species, like citrus and mandarin, shoot 
apical meristems (SAM) were treated ex situ, and after shoot induction 
grafted as scions onto trifoliate rootstocks (Aleza et al., 2009; Ollitrault 
et al., 2020). Such a method avoids the requirement for the introduction 
of material into in vitro culture that may pose considerable challenges for 
recalcitrant tree species or long-lived woody perennials. 
More powerful classes of antimitotic agents, such as the herbicides 
dinitroanilines (trifluralin and oryzalin) and phosphoric amides (ami-
prophos-methyl and butamiphos; Planchais et al., 2000) are not widely 
used to induce chromosome set doubling in trees. Oryzalin was however 
used with some success to induce polyploidy in Eucalyptus dunnii 
Maiden, but the survival rate was low (Castillo et al., 2020). 
7. Potential for polyploidy in forest tree breeding 
The induction of polyploidy in crop species often creates opportu-
nities and changes in breeding systems. Triploid breeding programs can 
be particularly beneficial, however there have been only few instances 
of implementation and evaluation in key forestry species, e.g., Acacia 
(Nghiem et al., 2018), Populus (Kang and Wei, 2022), Eucalyptus uro-
phylla S.T.Blake (Yang et al., 2018) and Betula (Mu et al.,2012a). 
Naturally occurring triploids have also been identified and selected for 
clonal propagation due to their potential for enhanced traits and gain 
(Quercus, Dzialuk et al., 2007; Prunus avium L., Serres-Giardi et al., 2010; 
Eucalyptus grandis x urophylla, Longui et al., 2021). The low fertility of 
triploid oaks, likely due to disrupted meiosis and pollen production with 
unbalanced chromosome complements, means their direct value for 
downstream breeding is low (Butorina, 1993). Overall, however, it 
would appear that the advantages of triploid breeding in forestry pro-
grams have not yet been fully realized. In contrast, horticultural triploid 
breeding programs are advanced and provide significant utility. For a 
large variety of crops elite diploid and tetraploid parental lines are bred 
to produce hybrid seed, almost all of which are triploid. These progenies 
offer many benefits including plants with a fixed heterotic growth 
advantage and a uniform phenotypic distribution, along with sterility 
and the absence of seeds (Sattler et al., 2016). Having triploid progeny 
has the added advantage of containing the germplasm and avoids the 
release of elite breeding lines with stacked traits including disease 
resistance into the natural environment. Horticultural seed production is 
often managed using crosses onto male diploid sterile acceptor lines 
(Cheng et al., 2022). In this case, nuclear or male cytoplasmic sterility, 
or even sometimes self-incompatibility are used to manage pollination 
of female acceptor lines with the tetraploid pollen sources. Hybrid 
production in this manner usually avoids, or provides a way to tolerate 
endosperm imbalance which can arise from interploidy crosses during 
hybrid seed development (Gehring and Satyaki, 2017). 
Production systems that include triploidy in forestry may require 
significant time for their development and assessment. Likewise, their 
appropriateness may need to be coordinated for forest biodiversity or 
the perceived risk from an invasive fertile polyploid forest tree species 
which may have a significant growth advantage (e.g. hybrid eucalypt 
species). Even so, polyploidization in forest breeding programs may 
provide other useful opportunities. Synthetic polyploid systems have 
been used to overcome breeding barriers, and perform wide hybridiza-
tions (Manzur et al., 2015; Ruiz et al., 2020), or regain fertility (Riese-
berg, 2001). While fertility is often unaffected in induced 
autopolyploids, since endosperm balance is unchanged during seed 
development, synthesized allopolyploid hybrids can have reduced 
fertility. Often the restoration of fertility occurs through further 
doubling of allopolyploids, and can be attributed to a number of specific 
mechanisms (Rieseberg, 2001). These include modifying the ploidal 
balance between subgenomes, balancing the divergence between the 
parental subgenomes, or eliminating of specific genomic sequences, and 
improving the stability of the hybrid genome. In other cases, 
post-zygotic atrophy can occur at the F1 generation (Manzur et al., 
2015), and fertile individuals are sometimes obtained by embryo rescue. 
Even considering those barriers, there are many examples where syn-
thetic polyploids have acted as a bridge between species of different 
ploidy levels, allowing new genetic diversity, via introgressive hybrid-
ization, to be tapped into plant and tree breeding programs. 
Changed ploidy levels can sometimes be associated with clonal 
reproduction via asexual seeds or apomixis (eg. Sorbus; Box 1). This is 
often observed at low frequency in tree species, and often unlikely to 
have significant impact on population structure, with the exception of 
Mangifera, Citrus and Sorbus for example, where obligate modes of 
apomixis can and do occur (Hamston et al., 2018; Wang et al., 2017a; 
Yadav et al., 2023). The molecular basis for apomixis is now well un-
derstood (Underwood and Mercier, 2022), and engineering of apomixis 
into different crops has been recently achieved (Vernet et al., 2022; 
Underwood et al., 2022). Similar to triploid breeding programs, 
apomixis offers the potential for the fixation of hybrid vigor, and a 
method to evaluate morphological plasticity and niche adaptability. 
Furthermore if asexual seed reproduction were ever to be introduced 
into key forestry species, individuals with polyploid genomes may be 
better suited for the expression of both parthenogenesis and modifier 
loci (Hojsgaard, 2018). Apomixis on the other hand, will not provide a 
suitable method of germplasm containment for an elite breed of forestry 
trees should that be necessary. 
8. Uses of polyploids in forestry 
The many examples of accelerated vegetative growth in polyploids 
(Beyaz et al., 2013, Chen et al., 2021) have led to an interest to test the 
potential of both natural and artificial polyploid trees for forestry pur-
poses. While examples of polyploid trees are numerous in horticulture, 
the number of natural polyploid tree species that are currently in use in 
forestry is relatively limited. Still, the list of currently ploidy-known 
trees and shrubs in Table S3 contains commercially used species, 
including many shrub species but also important forestry species such as 
Acer pseudoplatanus L., Fraxinus chinensis Roxb., and several tropical 
timber genera such as Shorea Roxb. ex C.F.Gaertn. and Cordia L. Trees 
that naturally display multiple levels of ploidy are predominantly found 
amongst angiosperm trees and provide valuable material for testing 
effects of ploidy on field performance, like Acacia senegal (Diallo et al., 
2016) and Populus tremuloides (Arno and Hammerly, 2020, Blonder 
et al., 2021). Betula (Table S2) contains several valuable polyploid 
species, including B. chinensis Maxim., which is one of the most valuable 
A. Ræbild et al.                                                                                                                                                                                                                                 
Forest Ecology and Management 560 (2024) 121767
9
timber trees in northern China (eFlora, 2023), and the North American 
paper birch (B. papyrifera Marshall, comprising tetra-, penta- and 
hexaploids), one of the most sought after wood tree species for building 
and other purposes (Furlow, 2023). In northern Europe, the tetraploid 
B. pubescens Ehrh. is a common species that has previously been bred for 
both better timber quality and growth rate with great efficiency 
(Niemisto et al., 2017). 
Recent studies have sought to specifically characterize the correla-
tion between ploidy levels and lignin contents in trees as wood with 
lower lignin content is a desirable trait for certain applications. In 
Arabidopsis, induced tetraploid plants producing higher biomass than 
the diploids also had a lower lignin content (Corneillie et al., 2019). 
However in wild-type Populus tremula x P. alba, the tetraploid plants had 
lower biomass production and a higher lignin content than the diploids 
(Wouters et al., 2022), whereas in a synthetic poplar allotriploid induced 
by Populus pseudosimonii, P. nigra ‘Zheyin3#’ and P. beijingensis hybrid-
ization, the lignin content was reduced compared to the diploids (Xu 
et al., 2022). A lower lignin content in triploids was also found in Populus 
x tomentosa Carriere (Yao and Pu, 1998) and Salix hybrids (Serapiglia 
et al., 2015). The mechanism suggests a regulatory function for lignin 
biosynthesis associated with triploids. 
In fruit trees, artificial polyploids are sometimes characterized by 
dwarfism (Ruiz et al., 2020). However, field trials of important forestry 
species, including Acacia senegal (Diallo et al., 2016), Liriodendron x 
sino-americanum P.C.Yieh ex C.B Shang & Z.R.Wang (Chen et al., 2021) 
and Populus tremula (Parnik et al., 2014) show increased growth in 
polyploids compared to diploids. In a short term experiment, triploid 
hybrid Populus clones grew faster than diploids and tetraploids formed 
from the same parental origins (Zhao et al., 2015; Zhang et al., 2019b). 
However, there was no unidirectional response of growth upon poly-
ploidization in Salix viminalis L., where clones of autotetraploids 
exhibited either faster or slower growth compared to the parental 
diploid (Dudits et al., 2016). Similar results were obtained in Populus 
hybrids where, depending on the line, polyploids generated by proto-
plast fusion showed both superior and inferior biomass compared to the 
parental lines (Hennig et al., 2015). Triploid tree species such as Chinese 
white poplar (Populus x tomentosa) and willow (Salix spp.) have been 
used as model tree species to explore growth traits. For these species, 
triploids had increased growth and a more desirable wood composition, 
which can be exploited in breeding programs aimed at optimizing bio-
fuel production (Zhang et al., 2012; 2013; Serapiglia et al., 2015). 
Other angiosperm trees with high commercial value have also been 
shown to develop better traits when growing as artificial polyploids. 
Paulownia Siebold & Succ. are adaptable and fast-growing deciduous 
trees that provide raw material for manufacturing and agroforestry, and 
many traits related to growth and stress resistance were found to be 
superior in the colchicine induced autotetraploid Paulownia australis 
(PA4) compared to the parental diploid (PA2) (Xu et al., 2015). 
Globally, Eucalyptus is the most important angiosperm tree genus for 
pulp production (Myburg et al., 2014). Efforts to improve wood traits 
through polyploidization have shown promising results for eucalypt 
hybrids (E. grandis x E. urophylla) where the wood from synthetic 
polyploid clones had lower basic density and longer fibers compared to 
diploids (da Silva Souza et al., 2021). The two parental genomes were 
also shown to differ significantly in the repertoire of duplicated genes 
and for structural variation (Shen et al., 2023), highlighting how allo-
polyploidization can benefit forestry related trait breeding through the 
combination of significant genome diversity. Artificially induced poly-
ploids have also been obtained for E. dunnii as part of the breeding 
program to obtain new genotypes with improved adaptability and 
possibly reduced flowering age (Castillo et al., 2020). However, in 
another study of E. grandis x E. urophylla hybrids, polyploids exhibited 
decreased growth compared to their diploid counterparts (da Silva 
Souza et al., 2021). Similar results were obtained in a study comparing 
polyploid and diploid E. polybractea R.T.Baker grown in field and 
greenhouse conditions where the polyploids were shorter and thinner 
than the diploids (Fernando et al., 2019). 
Since gymnosperm trees, in particular species within the genera 
Pinus L., Picea Mill. and Larix Mill., includes several commercially 
important species, efforts have been made to produce superior traits 
through the generation of colchicine-induced polyploids. In a 30 year- 
long study of polyploids from Pinus sylvestris L., Pinus contorta Doug-
las, Picea abies (L.) H. Karst. and Larix sibirica Ledeb. in Sweden 
(Johnsson, 1975), the trees remained tetraploid but cone production did 
not occur until 30 years of age. The pollen formation was abnormal, 
preventing generation of triploids and seed quality was very poor in the 
C1 generation generated from backcrosses to the diploid parents. As the 
polyploids displayed growth delays and even dwarf growth, further ef-
forts towards applying polyploids to these breeding programs were 
discouraged (Ahuja, 2005). 
9. Perspectives 
Forestry will play a significant role in regaining control of the 
terrestrial carbon cycle from the over-exploitation of fossil fuels, and 
polyploid trees could play an important role by accelerating biomass 
accumulation. For most forestry tree species, however, there is no data 
on the effects of increased ploidy on fitness. Increased knowledge of the 
potential benefits of elevated ploidy levels from either allo- or auto- 
polyploidization would directly benefit forestry and guide future 
research in this area. As we have reviewed above, increased ploidy may 
in some cases have positive outcomes on traits like growth, biomass, 
timber properties and resistance to climate related stressors. 
To address the knowledge gap in chromosome counts for plants, 
particularly trees, focused efforts in chromosome counting or flow 
cytometry are needed, especially in biodiversity hotspots such as Brazil, 
Southeast Asia, and Madagascar. Targeting selected forest tree genera 
for comprehensive chromosome counting and obtaining intraspecific 
chromosome numbers will aid in conservation efforts and help identify 
biodiversity (Severns & Liston, 2008). 
While numerous studies indicate that polyploidy leads to larger 
cellular structures at the leaf surface, there is little knowledge on how 
the structural development inside leaves, stems and roots are affected. 
This also means that links between anatomy and physiology are poorly 
understood for polyploids. In particular, the ratio between photosyn-
thesis and transpiration (water use efficiency) may be increased 
following polyploidization, but there is a large gap in data despite it 
being easily measurable using for example carbon isotopic discrimina-
tion. The often hypothesized superior performance of polyploids under 
high CO2 environments has received surprisingly little attention by 
physiologists and it should be a priority to test this, especially when 
combined with stress trials. 
Along with understanding the ecophysiological significance of 
polyploidy, experiments on the polyploidization of forest trees can 
further clarify the molecular basis for the control that genome size exerts 
on plant form, anatomy and physiology. Experimental polyploidization 
of key forest trees may also refine inferences on the paleo record espe-
cially for stomatal density/index relationships, since induced ploidal 
series could provide contemporaneous reference collections and extend 
data observations in the fossil record from the nearest living equivalents. 
A close monitoring of new polyploids under field conditions is necessary, 
not only to evaluate the performance outside laboratories and green-
houses, but also to evaluate the potential invasiveness if polyploids 
prove superior to conspecific diploids. 
Taken together, polyploidy provides substantial potential for 
breeding of both horticultural and forestry trees for traits facilitating 
adaptation to the changing climate, yet this potential needs to be studied 
on a case-by-case basis in different tree species. 
CRediT authorship contribution statement 
Jensen Anna Monrad: Writing – review & editing, Writing – 
A. Ræbild et al.                                                                                                                                                                                                                                 
Forest Ecology and Management 560 (2024) 121767
10
original draft. Immanen Juha: Writing – review & editing, Writing – 
original draft. Martens Helle Jakobe: Writing – review & editing, 
Writing – original draft, Visualization. Koutouleas Athina: Writing – 
review & editing, Writing – original draft, Visualization, Data curation. 
Stromvik Martina: Writing – review & editing, Writing – original draft. 
Ræbild Anders: Writing – review & editing, Writing – original draft, 
Visualization, Project administration, Methodology, Funding acquisi-
tion, Formal analysis, Conceptualization. Salojarvi Jarkko: Writing – 
review & editing, Writing – original draft. Vivian-Smith Adam: Writing 
– review & editing, Writing – original draft, Visualization. Egertsdotter 
Ulrika: Writing – review & editing, Writing – original draft, Conceptu-
alization. Vatanparast Mohammad: Writing – review & editing, 
Writing – original draft, Visualization, Formal analysis, Data curation. 
Anamthawat-Jonsson Kesara: Writing – review & editing, Writing – 
original draft, Formal analysis, Data curation. Nieminen Kaisa: Writing 
– review & editing, Writing – original draft. Roper Anna-Catharina: 
Writing – review & editing, Writing – original draft, Visualization. 
Olofsson Jill Katharina: Writing – review & editing, Writing – original 
draft, Visualization. 
Declaration of Competing Interest 
The authors declare that they have no known competing financial 
interests or personal relationships that could have appeared to influence 
the work reported in this paper. 
Data availability 
Data are attached as supplementary materials. 
Acknowledgments 
This review is a result of collaboration within the Nordic Network for 
Polyploid Trees (POLYTREE), supported by the Nordic Forestry 
Research (SNS), grant no. N2022–1. J.I. was additionally supported by 
Suomen Luonnonvarain tutkimussaatio (20220013/20230059) and K. 
N. by the Research Council of Finland CoE in Tree Biology 
(346139;346141) and Jane and Aatos Erkko Foundation (200003). We 
thank the two anonymous reviewers for their constructive suggestions to 
improve the manuscript. 
List of supplementary materials 
Supplementary data associated with this article can be found in the 
online version at doi:10.1016/j.foreco.2024.121767.: 
Figure S1. Polyploid occurrence in different taxa. a) Bar chart rep-
resenting the frequency of polyploid tree/shrub species per family. b) 
Bar chart representing the number of polyploid species for genera with 
the highest number of species. c) Bar chart representing the frequency of 
polyploid tree/shrub species per genus. Tree genera such as Alnus, Tilia, 
Sorbus, Carya and Betula are among the top forest trees. Our approach to 
classify the polyploids followed Rice et al. (2019) in which polyploids 
are explicitly defined as those taxa that have undergone a poly-
ploidization event since divergence from the most recent common an-
cestors. The species are considered diploid when all chromosomes 
counting for the taxa are diploid, whereas species with at least one re-
cord of ploidy are shown as polyploid. 
Figure S2. Distribution of ploidy levels of Betula species using Eye-
Chrom R package (Rivero et al., 2019). 
Table S1. Literature data on anatomy and physiology of polyploid 
trees (Excel file). 
Table S2. List of 57 ploidy-known, naturally occurring Betula species, 
with geographical distribution, from the total of about 65 species 
worldwide. (Word file). 
Table S3. List of currently known polyploid trees and shrubs based on 
the chromosome counts database (Rice et al., 2019), retrieved April 1, 
2023 (Excel file). 
References 
Abdolinejad, R., Shekafandeh, A., 2022. Tetraploidy confers superior in vitro water-stress 
tolerance to the fig tree (Ficus carica) by reinforcing hormonal, physiological, and 
biochemical defensive systems. Front. Plant Sci. 12, 796215 https://doi.org/ 
10.3389/fpls.2021.796215. 
Ahuja, M.R., 2005. Polyploidy in gymnosperms: revisited. Silvae Genet. 54, 59–69. 
https://doi.org/10.1515/sg-2005-0010. 
Aleza, P., Juarez, J., Ollitrault, P., et al., 2009. Production of tetraploid plants of non 
apomictic citrus genotypes. Plant Cell Rep. 28, 1837–1846. https://doi.org/ 
10.1007/s00299-009-0783-2. 
Alix, K., Gerard, P.R., Schwarzacher, T., Heslop-Harrison, J.S., 2017. Polyploidy and 
interspecific hybridization: partners for adaptation, speciation and evolution in 
plants. Ann. Bot. 120 (2), 183–194. https://doi.org/10.1093/aob/mcx079. 
Allario, T., Brumos, J., Colmenero-Flores, J.M., Iglesias, D.J., Pina, J.A., Navarro, L., 
Talon, M., Ollitrault, P., Morillon, R., 2013. Tetraploid Rangpur lime rootstock 
increases drought tolerance via enhanced constitutive root abscisic acid production. 
Plant, Cell Environ. 36 (4), 856–868. https://doi.org/10.1111/PCE.12021. 
Appanah, S., Turnbull, J.M., 1998. A review of dipterocarps: taxonomy.. In: In: Ecology, 
and Silviculture CIFOR, Bogor, Indonesia, p. 219. 
Arno, S.F., Hammerly, R.P., 2020. Northwest trees: identifying & understanding the 
region’s native trees. Mountaineers Books, Seattle, field guide ed. pp. 203–208. ISBN 
978-1-68051-329-5. OCLC 114123546. 
Ashburner, K., McAllister, H.A., 2013. The Genus Betula: A Taxonomic Revision of 
Birches. Royal Botanic Garden Kew Publishing, London. ISBN-13: 978-1842461419.  
Barcelo-Anguiano, M., Holbrook, N.M., Hormaza, J.I., Losada, J.M., 2021. Changes in 
ploidy affect vascular allometry and hydraulic function in Mangifera indica trees. 
Plant J. 108 (2), 541–554. https://doi.org/10.1111/tpj.15460. 
Bar-On, Y.M., Phillips, R., Milo, R., 2018. The biomass distribution on Earth. Proc. Natl. 
Acad. Sci. USA 115 (25), 6506–6511. https://doi.org/10.1073/pnas.1711842115. 
Beaulieu, J.M., Leitch, I.J., Patel, S., Pendharkar, A., Knight, C.A., 2008. Genome size is a 
strong predictor of cell size and stomatal density in angiosperms. N. Phytol. 179 (4), 
975–986. https://doi.org/10.1111/J.1469-8137.2008.02528.X. 
Beck, S.L., Fossey, A., Mathura, S., 2003. Ploidy determination of black wattle (Acacia 
mearnsii) using stomatal chloroplast counts. South. Afr. For. J. 198 (1), 79–82. 
https://doi.org/10.1080/20702620.2003.10431738. 
Beech, E., Rivers, M., Oldfield, S., Smith, P.P., 2017. GlobalTreeSearch: the first complete 
global database of tree species and country distributions. J. Sustain. For. 36 (5), 
454–489. https://doi.org/10.1080/10549811.2017.1310049. 
Beyaz, R., Alizadeh, B., Gürel, S., Ozcan, S.F., Yildiz, M., 2013. Sugar beet (Betavulgaris 
L.) growth at different ploidy levels. Caryologia 66 (1), 90–95. https://doi.org/ 
10.1080/00087114.2013.787216. 
Bird, K.A., VanBuren, R., Puzey, J.R., Edger, P.P., 2018. The causes and consequences of 
subgenome dominance in hybrids and recent polyploids. N. Phytol. 220, 87–93. 
https://doi.org/10.1111/nph.15256. 
Blakesley, D., Allen, A., Pellny, T.K., Roberts, A.V., 2002. Natural and induced polyploidy 
in Acacia dealbata Link. and Acacia mangium Willd. Ann. Bot. 90, 391–398. https:// 
doi.org/10.1093/aob/mcf202. 
Blonder, B., Ray, C.A., Walton, J.A., Castaneda, M., Chadwick, K.D., Clyne, M.O., 
Gauzere, P., Iversen, L.L., Lusk, M., Strimbeck, R., Troy, S., Mock, K.E., 2021. 
Cytotype and genotype predict mortality and recruitment in Colorado quaking aspen 
(Populus tremuloides. Ecol. Appl. 31 (8), e02438 https://doi.org/10.1002/ 
eap.2438. 
Borges, L.A., Souza, L.G.R., Guerra, M., et al., 2012. Reproductive isolation between 
diploid and tetraploid cytotypes of Libidibia ferrea (ˆ Caesalpinia ferrea) 
(Leguminosae): ecological and taxonomic implications. Plant Syst. Evol. 298, 
1371–1381. https://doi.org/10.1007/s00606-012-0643-3. 
Bures, P., Elliott, T.L., Veselý, P., Smarda, P., Forest, F., Leitch, I.J., Nic Lughadha, E., 
Soto Gomez, M., Pironon, S., Brown, M.J.M., Smerda, J., Zedek, F., 2024. The global 
distribution of angiosperm genome size is shaped by climate. N. Phytol. https://doi. 
org/10.1111/nph.19544. 
Butorina, A.K., 1993. Cytogenetic study of diploid and spontaneous triploid oaks, Quercus 
robur L. Ann. For. Sci. 50, 144–150. https://doi.org/10.1051/forest:19930714. 
Cao, X., Zhai, X., Xu, E., Zhao, Z., Fan, G., 2020. Genome-wide identification of candidate 
genes related to disease resistance and high biomass in tetraploid Paulownia. Acta 
Physiol. Plant. 42 (11), 1–10. https://doi.org/10.1007/s11738-020-03160-7. 
Carlson, C.H., Smart, L.B., 2022. Heterosis for biomass-related traits in interspecific 
triploid hybrids of willow (Salix spp.). BioEnergy Res. 15 (2), 1042–1056. https:// 
doi.org/10.1007/s12155-021-10305-0. 
Carlson, C.H., Choi, Y., Chan, A.P., Town, C.D., Smart, L.B., 2022. Nonadditive gene 
expression is correlated with nonadditive phenotypic expression in interspecific 
triploid hybrids of willow (Salix spp.). G3 Genes|Genomes|Genet. 12 (3) https://doi. 
org/10.1093/g3journal/jkab436. 
Castillo, A., Lope, V., Tavare, E., Santi~naque, F., Dalla Rizza, M., 2020. Polyploid 
induction of Eucalyptus dunnii Maiden to generate variability in breeding programs. 
Agrociencia Urug. 24, 381. https://doi.org/10.31285/AGRO.24.381. 
Cavalier-Smith, T., 2005. Economy, speed and size matter: evolutionary forces driving 
nuclear genome miniaturization and expansion. Ann. Bot. 95, 147–175. https://doi. 
org/10.1093/aob/mci010. 
Chen, T., Sheng, Y., Hao, Z., Long, X., Fu, F., Liu, Y., Tang, Z., Ali, A., Peng, Y., Liu, Y., 
Lu, L., 2021. Transcriptome and proteome analysis suggest enhanced photosynthesis 
in tetraploid Liriodendron sino-americanum. Tree Physiol. 41 (10), 1953–1971. 
https://doi.org/10.1093/treephys/tpab039. 
A. Ræbild et al.                                                                                                                                                                                                                                 
Forest Ecology and Management 560 (2024) 121767
11
Chen, Z.J., Sreedasyam, A., Ando, A., et al., 2020. Genomic diversifications of five 
Gossypium allopolyploid species and their impact on cotton improvement. Nat. 
Genet. 52, 525–533. https://doi.org/10.1038/s41588-020-0614-5. 
Cheng, Z., Song, W., Zhang, X., 2022. Genic male and female sterility in vegetable crops. 
Hortic. Res., 10 (1), uhac232. https://doi.org/10.1093/hr/uhac232. 
Chokchaichamnankit, P., Anamthawat-Jonsson, K., Chulalaksananukul, W., 2008. 
Chromosomal mapping of 18S–25S and 5S ribosomal genes on 15 species of Fagaceae 
from Northern Thailand. Silvae Genet. 57 (1-6), 5–13. https://doi.org/10.1515/sg- 
2008-0002. 
Clark, J.W., Donoghue, P.C.J., 2018. Whole-genome duplication and plant 
macroevolution. Trends Plant Sci. 23 (10), 933–945. https://doi.org/10.1016/j. 
tplants.2018.07.006. 
Comai, L., 2005. The advantages and disadvantages of being polyploid. Nat. Rev. Genet. 
6 (11), 836–846. https://doi.org/10.1038/nrg1711. 
Conant, G.C., Birchler, J.A., Pires, J.C., 2014. Dosage, duplication, and diploidization: 
clarifying the interplay of multiple models for duplicate gene evolution over time. 
Curr. Opin. Plant Biol. 19, 91–98. https://doi.org/10.1016/j.pbi.2014.05.008. 
Conover, J.L., Wendel, J.F., 2022. Deleterious Mutations accumulate faster in 
allopolyploid than diploid cotton (Gossypium) and unequally between subgenomes. 
Mol. Biol. Evol. 39 (2), msac024 https://doi.org/10.1093/molbev/msac024. 
Corneillie, S., de Storme, N., van Acker, R., Fangel, J.U., de Bruyne, M., de Rycke, R., 
Geelen, D., Willats, W.G.T., Vanholme, B., Boerjan, W., 2019. Polyploidy affects 
plant growth and alters cell wall composition. Plant Physiol. 179 (1), 74–87. https:// 
doi.org/10.1104/PP.18.00967. 
Darrow, G., 1950. Polyploidy in fruit improvement. Sci. Mon. 70, 211–219.. https 
://www.jstor.org/stable/19921.  
da Silva Souza, T., Daolio, M.F., Mori, F.A., et al., 2021. Polyploidy as a strategy to 
improve the industrial quality of eucalypt wood. Wood Sci. Technol. 55, 181–193. 
https://doi.org/10.1007/s00226-020-01236-8. 
De Baerdemaeker, N.J., Hias, N., Van den Bulcke, J., Keulemans, W., Steppe, K., 2018. 
The effect of polyploidization on tree hydraulic functioning. Am. J. Bot. 105 (2), 
161–171. https://doi.org/10.1002/ajb2.1032. 
de Groot, W.J., Thomas, P.A., Wein, R.W., 1997. Betula nana L. and Betula glandulosa 
Michx. J. Ecol. 85, 241–264. https://doi.org/10.2307/2960655. 
Diallo, A.M., Kjær, E.D., Ræbild, A., et al., 2023. Coexistence of diploid and polyploid 
Acacia senegal (L. Willd.) and its implications for interploidy pollination. N. For. 54, 
67–82. https://doi.org/10.1007/s11056-021-09901-x. 
Diallo, A.M., Nielsen, L.R., Kjær, E.D., Petersen, K.K., Ræbild, A., 2016. Polyploid can 
confer superiority to West African Acacia senegal (L.) Willd. trees. Front. Plant Sci. 7, 
821. https://doi.org/10.3389/fpls.2016.00821. 
Diatta, O., Kjaer, E.D., Diallo, A.M., Nielsen, L.R., Novak, V., Sanogo, D., Laursen, K.H., 
Hansen, J.K., Ræbild, A., 2022. Leaf morphology and stable isotope ratios of carbon 
and nitrogen in Acacia senegal (L.) Wild trees vary with climate at the geographic 
origin and ploidy level. Trees 36 (1), 295–312. https://doi.org/10.1007/s00468- 
021-02206-8. 
Duan, T., Sicard, A., Glemin, S., Lascoux, M., 2023. Separating phases of allopolyploid 
evolution with resynthesized and natural Capsella bursa-pastoris. bioRxiv. https:// 
doi.org/10.1101/2023.04.17.537266. 
Dudits, D., Torok, K., Cseri, A., Paul, K., Nagy, A.V., Nagy, B., Sass, L., Ferenc, G., 
Vankova, R., Dobrev, P., Vass, I., 2016. Response of organ structure and physiology 
to autotetraploidization in early development of energy willow Salix viminalis. Plant 
Physiol. 170 (3), 1504–1523. https://doi.org/10.1104/pp.15.01679. 
Dzialuk, A., Chybicki, I., Welc, M., Sliwinska, E., Burczyk, J., 2007. Presence of triploids 
among oak species. Ann. Bot. 99, 959–964. https://doi.org/10.1093/aob/mcm043. 
Ebadi, M., Bafort, Q., Mizrachi, E., Audenaert, P., Simoens, P., Van Montagu, M., 
Bonte, D., Van de Peer, Y., 2023. The duplication of genomes and genetic networks 
and its potential for evolutionary adaptation and survival during environmental 
turmoil. Proc. Natl. Acad. Sci. USA 120 (41), e2307289120. https://doi.org/ 
10.1073/pnas.2307289120. 
eFlora, 2023. Betula Linnaeus. Flora of China, vol 4, p 304. Published on the Internet 
http://www.eforas.org [accessed 20 March 2023]. Missouri Botanical Garden, St. 
Louis, MO & Harvard University Herbaria, Cambridge, MA. 
Eisenring, M., Lindroth, R.L., Flansburg, A., Giezendanner, N., Mock, K.E., Kruger, E.L., 
2023. Genotypic variation rather than ploidy level determines functional trait 
expression in a foundation tree species in the presence and absence of environmental 
stress. Ann. Bot. 131 (1), 229–242. https://doi.org/10.1093/aob/mcac071. 
Faizullah, L., Morton, J.A., Hersch-Green, E.I., Walczyk, A.M., Leitch, A.R., Leitch, I.J., 
2021. Exploring environmental selection on genome size in angiosperms. Trends 
Plant Sci. 26 (10), 1039–1049. https://doi.org/10.1016/j.tplants.2021.06.001. 
Fernando, S.C., Goodger, J.Q., Chew, B.L., Cohen, T.J., Woodrow, I.E., 2019. Induction 
and characterisation of tetraploidy in Eucalyptus polybractea RT Baker. Ind. Crops 
Prod. 140, 111633 https://doi.org/10.1016/j.indcrop.2019.111633. 
Furlow, J.J., 2023. Betula L. In: Flora of North America Editorial Committee, eds. 1993‡. 
Flora of North America North of Mexico [Online]. [accessed 20 March 2023]. New 
York and Oxford. Vol. 3. http://beta.floranorthamerica.org/Betula. 
García-García, A.L., Grajal-Martín, M.J., Gonzalez-Rodríguez, A.M., 2020. 
Polyploidization enhances photoprotection in the first stages of Mangifera indica. 
Sci. Hortic. 264, 109198 https://doi.org/10.1016/j.scienta.2020.109198. 
Gehring, M., Satyaki, P.R., 2017. Endosperm and imprinting, inextricably linked. Plant 
Physiol. 173 (1), 143–154. https://doi.org/10.1104/pp.16.01353. 
Greer, B.T., Still, C., Cullinan, G.L., Brooks, J.R., Meinzer, F.C., 2018. Polyploidy 
influences plant–environment interactions in quaking aspen (Populus tremuloides 
Michx.). Tree Physiol. 38 (4), 630–640. https://doi.org/10.1093/treephys/tpx120. 
Hao, G.Y., Lucero, M.E., Sanderson, S.C., Zacharias, E.H., Holbrook, N.M., 2013. 
Polyploidy enhances the occupation of heterogeneous environments through 
hydraulic related trade-offs in Atriplex canescens (Chenopodiaceae). N. Phytol. 197 
(3), 970–978. https://doi.org/10.1111/nph.12051. 
Hajrudinovic, A., Siljak-Yakovlev, S., Brown, S.C., Pustahija, F., Bourge, M., Ballian, D., 
Bogunic, F., 2015. When sexual meets apomict: Genome size, ploidy level and 
reproductive mode variation of Sorbus aria s.l. and S. austriaca (Rosaceae) in Bosnia 
and Herzegovina. Ann. Bot. 116 (2), 301–312. https://doi.org/10.1093/aob/ 
mcv093. 
Hamston, T.J., de Vere, N., King, R.A., Pellicer, J., Fay, M.F., Cresswell, J.E., Stevens, J. 
R., 2018. Apomixis and hybridization drives reticulate evolution and phyletic 
differentiation in Sorbus L.: implications for conservation. Front. Plant Sci. 9, 1796 
https://doi.org/10.3389%2Ffpls.2018.01796.  
Hartmann, H., Bastos, A., Das, A.J., Esquivel-Muelbert, A., Hammond, W.M., Martínez- 
Vilalta, J., McDowell, N.G., Powers, J.S., Pugh, T.A.M., Ruthrof, K.X., Allen, C.D., 
2022. Climate change risks to global forest health: emergence of unexpected events 
of elevated tree mortality worldwide, 673-702 Annu. Rev. Plant Biol. 73 (1). https:// 
doi.org/10.1146/annurev-arplant-102820-012804. 
Hedden, P., 2003. The genes of the green revolution. Trends Genet. 19 (1), 5–9. https:// 
doi.org/10.1016/s0168-9525(02)00009-4. 
Hennig, A., Kleinschmit, J.R.G., Schoneberg, S., Loffler, S., Janßen, A., Polle, A., 2015. 
Water consumption and biomass production of protoplast fusion lines of poplar 
hybrids under drought stress. Front. Plant Sci. 6, 330. https://doi.org/10.3389/ 
fpls.2015.00330. 
Henry, T.A., Bainard, J.D., Newmaster, S.G., 2014. Genome size evolution in Ontario 
ferns (Polypodiidae): evolutionary correlations with cell size, spore size, and habitat 
type and an absence of genome downsizing. Genome 57 (10), 555–566. https://doi. 
org/10.1139/gen-2014-0090. 
Hodgson, J.G., Sharafi, M., et al., 2010. Stomatal vs. genome size in angiosperms: the 
somatic tail wagging the genomic dog? Ann. Bot. 105 (4), 573–584. https://doi.org/ 
10.1093/aob/mcq011. 
Hojsgaard, D., 2018. Transient activation of apomixis in sexual neotriploids may retain 
genomically altered states and enhance polyploid establishment. Front. Plant Sci. 9, 
230. https://doi.org/10.3389/fpls.2018.00230. 
Hu, G., Feng, J., Xiang, X., Wang, J., Salojarvi, J., Liu, C., Wu, Z., Zhang, J., Liang, X., 
Jiang, Z., et al., 2022. Two divergent haplotypes from a highly heterozygous lychee 
genome suggest independent domestication events for early and late-maturing 
cultivars. Nat. Genet. 54, 73–83. https://doi.org/10.1038/s41588-021-00971-3. 
Johnsson, H., 1945. Interspecific hybridization within the genus Betula. Hereditas 31, 
163–176. https://doi.org/10.1111/j.1601-5223.1945.tb02752.x. 
Johnsson, H., 1946. Chromosome numbers of twin plants of Quercus robur and Fagus 
silvatica. Hereditas 32 (3-4), 469–472. https://doi.org/10.1111/j.1601-5223.1946. 
tb02787.x. 
Johnsson, H., 1975. Observations on induced polyploidy in some conifers (Pinus 
sylvestris, P. contorta, Picea abies and Larix sibirica). Silvae Genet. 24 (2/3), 62–68. 
Jung, C., Till, B., 2021. Mutagenesis and genome editing in crop improvement: 
perspectives for the global regulatory landscape. Trends Plant Sci. 26 (12), 
1258–1269. https://doi.org/10.1016/j.tplants.2021.08.002. 
Kang, X., Wei, H., 2022. Breeding polyploid Populus: progress and perspective. For. Res. 
2 (4) https://doi.org/10.48130/fr-2022-0004. 
Kaplan, Z., Danihelka, J., Chrtek, J., et al., 2019. Klíc ke kvetene Ceske republiky [Key to 
the flora of the Czech Republic]. ACADEMIA,, Praha, p. 1168 reprinted 2021.  
Karlin, E.F., Smouse, P.E., 2017. Allo-allo-triploid Sphagnum  falcatulum: single 
individuals contain most of the Holantarctic diversity for ancestrally indicative 
markers. Ann. Bot. 120 (2), 221–231. https://doi.org/10.1093/aob/mcw269. 
Katagiri, Y., Hasegawa, J., Fujikura, U., Hoshino, R., Matsunaga, S., Tsukaya, H., 2016. 
The coordination of ploidy and cell size differs between cell layers in leaves. 
Development 143 (7), 1120–1125. https://doi.org/10.1242/dev.130021. 
Knight, C.A., Molinari, N.A., Petrov, D.A., 2005. The large genome constraint hypothesis: 
evolution, ecology and phenotype. Ann. Bot. 95 (1), 177–190. https://doi.org/ 
10.1093/aob/mci011. 
Lefort, F., Lally, M., Thompson, D., Douglas, G.C., 1998. Morphological traits, 
microsatellite fingerprinting and genetic relatedness of a stand of elite oaks(Q. robur 
L.) at Tullynally, Ireland. Silvae Genet. 47 (5-6), 257–262. 
Lefort, F., Douglas, G.C., Thompson, D., 2000. Microsatellite DNA profiling of 
phenotypically selected clones of Irish oak (Quercus spp.) and ash (Fraxinus excelsior 
L.). Silvae Genet. 49 (1), 21–28. 
Lepais, O., Muller, S.D., Ben Saad-Limam, S., Benslama, M., Rhazi, L., Belouahem- 
Abed, D., Daoud-Bouattour, A., Gammar, A.M., Ghrabi-Gammar, Z., Bacles, C.F.E., 
2013. High genetic diversity and distinctiveness of rear-edge climate relicts 
maintained by ancient tetraploidisation for Alnus glutinosa. PLOS One 8 (9), e75029. 
https://doi.org/10.1371/journal.pone.0075029. 
Li, W.L., Berlyn, G.P., Ashton, P.M.S., 1996. Polyploids and their structural and 
physiological characteristics relative to water deficit in Betula papyrifera 
(Betulaceae). Am. J. Bot. 83 (1), 15–20. https://doi.org/10.1002/j.1537-2197.1996. 
tb13869.x. 
Li, W.-D., Biswas, D.K., Xu, H., Xu, C.Q., Wang, X.Z., Liu, J.-K., Jiang, G.M., 2009. 
Photosynthetic responses to chromosome doubling in relation to leaf anatomy in 
Lonicera japonica subjected to water stress. Funct. Plant Biol. 36, 783–792. https:// 
doi.org/10.1071/FP09022. 
Liang, Z., Schnable, J.C., 2018. Functional divergence between subgenomes and gene 
pairs after whole genome duplications. Mol. Plant 11 (3), 388–397. https://doi.org/ 
10.1016/j.molp.2017.12.010. 
Liqin, G., Jianguo, Z., Xiaoxia, L., et al., 2019. Polyploidy-related differential gene 
expression between diploid and synthesized allotriploid and allotetraploid hybrids of 
Populus. Mol. Breed. 39 (69) https://doi.org/10.1007/s11032-019-0975-6. 
A. Ræbild et al.                                                                                                                                                                                                                                 
Forest Ecology and Management 560 (2024) 121767
12
Liu, G., Li, Z., Bao, M., 2007. Colchicine-induced chromosome doubling in Platanus 
acerifolia and its effect on plant morphology. Euphytica 157, 145–154. https://doi. 
org/10.1007/s10681-007-9406-6. 
Liu, W., Zheng, Y., Song, S., Huo, B., Li, D., Wang, J., 2018. In vitro induction of 
allohexaploid and resulting phenotypic variation in Populus. Plant Cell, Tissue 
Organ Cult. (PCTOC) 134, 183–192. https://doi.org/10.1007/s11240-018-1411-z. 
Lomax, B.H., Hilton, J., Bateman, R.M., Upchurch, G.R., Lake, J.A., Leitch, I.J., 
Cromwell, A., Knight, C.A., 2014. Reconstructing relative genome size of vascular 
plants through geological time. N. Phytol. 201 (2), 636–644. https://doi.org/ 
10.1111/NPH.12523. 
Longui, E.L., Custodio, G.H., Amorim, E.P., Júnior, F.G., da, S., Oda, S., Souza, I.C.G., 
2021. Differences in wood properties among Eucalyptus grandis and Eucalyptus 
grandis x Eucalyptus urophylla with different degrees of ploidy. 
e395101624035–e395101624035 Res., Soc. Dev. 10 (16). https://doi.org/ 
10.33448/RSD-V10I16.24035. 
Lourkisti, R., Froelicher, Y., Herbette, S., Morillon, R., Giannettini, J., Berti, L., 
Santini, J., 2021a. Triploidy in citrus genotypes improves leaf gas exchange and 
antioxidant recovery from water deficit. Front. Plant Sci. 11, 615335 https://doi. 
org/10.3389/fpls.2020.615335. 
Lourkisti, R., Froelicher, Y., Herbette, S., Morillon, R., Tomi, F., Gibernau, M., 
Giannettini, J., Berti, L., Santini, J., 2020. Triploid citrus genotypes have a better 
tolerance to natural chilling conditions of photosynthetic capacities and specific leaf 
volatile organic compounds. Front. Plant Sci. 11, 330. https://doi.org/10.3389/ 
fpls.2020.00330. 
Lourkisti, R., Oustric, J., Quilichini, Y., Froelicher, Y., Herbette, S., Morillon, R., Berti, L., 
Santini, J., 2021b. Improved response of triploid citrus varieties to water deficit is 
related to anatomical and cytological properties. Plant Physiol. Biochem. 162, 
762–775. https://doi.org/10.1016/j.plaphy.2021.03.041. 
Lourkisti, R., Froelicher, Y., Morillon, R., Berti, L., Santini, J., 2022. Enhanced 
photosynthetic capacity, osmotic adjustment and antioxidant defenses contribute to 
improve tolerance to moderate water deficit and recovery of triploid citrus 
genotypes. Antioxidants 11 (3), 562. https://doi.org/10.3390/antiox11030562. 
Luo, Q., Peng, M., Zhang, X., Lei, P., Ji, X., Chow, W., Meng, F., Sun, G., 2017. 
Comparative mitochondrial proteomic, physiological, biochemical and 
ultrastructural profiling reveal factors underpinning salt tolerance in tetraploid black 
locust (Robinia pseudoacacia L.). BMC Genom. 18 (1), 1–23. https://doi.org/ 
10.1186/s12864-017-4038-2. 
McAllister, H.A., 2005. The Genus Sorbus: Mountain Ashes and Other Rowans. Kew, 256 
pp. ISBN 10-1842460889. 
Maherali, H., Walden, A.E., Husband, B.C., 2009. Genome duplication and the evolution 
of physiological responses to water stress. N. Phytol. 184, 721–731. https://doi.org/ 
10.1111/j.1469-8137.2009.02997.x. 
Mallet, J., 2007. Hybrid speciation. Nature 446, 279–283. https://doi.org/10.1038/ 
nature05706. 
Manzur, J.P., Fita, A., Prohens, J., Rodríguez-Burruezo, A., 2015. Successful wide 
hybridization and introgression breeding in a diverse set of common peppers 
(capsicum annuum) using different cultivated Ají (C. baccatum) accessions as donor 
parents. PLOS One 10 (12), e0144142. https://doi.org/10.1371/journal. 
pone.0144142. 
McClintock, B., 1984. The significance of responses of the genome to challenge. Science 
226, 792–801. https://doi.org/10.1126/science.15739260. 
Meason, D.F., Kennedy, S.G., Dungey, H.S., 2016. Two New Zealand-based common 
garden experiments of the range-wide ‘Kuser’clonal collection of Sequoia 
sempervirens reveal patterns of provenance variation in growth and wood 
properties. N. For. 47, 635–651. https://doi.org/10.1007/s11056-016-9535-7. 
Mendes-Rodrigues, C., Marinho, R.C., Balao, F., Arista, M., Ortiz, P.L., Carmo- 
Oliveira, R., Oliveira, P.E., 2019. Reproductive diversity, polyploidy, and 
geographical parthenogenesis in two Eriotheca (Malvaceae) species from Brazilian 
Cerrado. Perspect. Plant Ecol., Evol. Syst. 36, 1–12. https://doi.org/10.1016/j. 
ppees.2018.11.001. 
Motosugi, H., Okudo, K., Kataoka, D., Naruo, T., 2002. Comparison of growth 
characteristics between diploid and colchicine-induced tetraploid grape rootstocks. 
J. Jpn. Soc. Hort. Sci. 71, 335–341. https://doi.org/10.2503/jjshs.71.335. 
Mu, H.Z., Liu, Z.J., Lin, L., Li, H.Y., Jiang, J., Liu, G.F., 2012b. Transcriptomic analysis of 
phenotypic changes in birch (Betula platyphylla) autotetraploids. Int. J. Mol. Sci. 13 
(10), 13012–13029. https://doi.org/10.3390/ijms131013012. 
Mu, H., Jiang, J., Li, H., Liu, G., 2012a. Seed vigor, photosynthesis and early growth of 
saplings of different triploid Betula families. Dendrobiology 68, 11–20. 
Myburg, A.A., Grattapaglia, D., Tuskan, G.A., Hellsten, U., Hayes, R.D., Grimwood, J., 
Jenkins, J., Lindquist, E., Tice, H., Bauer, D., Goodstein, D.M., 2014. The genome of 
Eucalyptus grandis. Nature 510 (7505), 356–362. https://doi.org/10.1038/ 
nature13308. 
Naujoks, G., Hertel, H., Ewald, D., 1995. Characterization and propagation of an adult 
triploid pedunculate oak (Quercus robur L.). Silvae Genet. 44 (5-6), 282–286. 
Niemisto, P., Kojola, S., Ahtikoski, A., Laiho, R., 2017. From useless thickets to valuable 
resource? – Financial performance of downy birch management on drained 
peatlands. Silva Fenn. 51, 3. https://doi.org/10.14214/sf.2017. 
Nghiem, C.Q., Griffin, R.A., Harbard, J.L., Harwood, C.E., Le, S., Nguyen, K.D., Pham, B. 
V., 2018. Reduced fertility in triploids of Acacia auriculiformis and its hybrid with A. 
mangium. Euphytica 214, 77. https://doi.org/10.1007/s10681-018-2157-8. 
Nobel, P.S., 1999. Leaves and fluxes. Physicochemical & Environmental Plant 
Physiology, 4th ed. Academic Press,, San Diego, pp. 364–437. 
Oliveira, W., Silva, J.L.S., Cruz-Neto, O., et al., 2022. Higher frequency of legitimate 
pollinators and fruit set of autotetraploid trees of Libidibia ferrea (Leguminosae) 
compared to diploids in a mixed tropical urban population. J. Plant Res. 135, 
235–245. https://doi.org/10.1007/s10265-022-01373-0. 
Ollitrault, P., Germana, M.A., Froelicher, Y., Cuenca, J., Aleza, P., Morillon, R., 
Grosser, J.W., Guo, W., 2020. Ploidy manipulation for citrus breeding, genetics, and 
genomics. In: Gentile, A., La Malfa, S., Deng, Z. (Eds.), The Citrus Genome. 
Compendium of Plant Genomes. Springer,, Cham. https://doi.org/10.1007/978-3- 
030-15308-3_6.  
Ohri, D., 2021. Polyploidy in gymnosperms - a reappraisal. Silvae Genet. 70 (1), 22–38. 
https://doi.org/10.2478/sg-2021-0003. 
Otto, S.P., Whitton, J., 2000. Polyploid incidence and evolution. Annu. Rev. Genet. 34 
(1), 401–437 https://www.annualreviews.org/doi/pdf/10.1146/annurev. 
genet.34.1.401.  
Patel, N., Medina, R., Johnson, M.G., Goffient, B., 2021. Karyotypic diversity and cryptic 
speciation: Have we vastly underestimated moss species diversity? Bryophyt. Divers. 
Evol. 43 (1), 150–163. https://doi.org/10.11646/bde.43.1.12. 
Perera-Castro, A.V., Hernandez, B., Grajal-Martín, M.J., Gonzalez-Rodríguez, A.M., 2023. 
Assessment of drought stress tolerance of mangifera indica L. Autotetraploids. 
Agronomy 13 (1), 277. https://doi.org/10.3390/agronomy13010277. 
Pellicer, J., Hidalgo, O., Dodsworth, S., Leitch, I.J., 2018. Genome size diversity and its 
impact on the evolution of land plants. Genes 9 (2), 88. https://doi.org/10.3390/ 
genes9020088. 
Planchais, S., Glab, N., Inze, D., Bergounioux, C., 2000. Chemical inhibitors: a tool for 
plant cell cycle studies. FEBS Lett. 476 (1-2), 78–83. https://doi.org/10.1016/s0014- 
5793(00)01675-6. 
Pustovoitova, T.N., Eremin, G.V., Rassvetaeva, E.G., Zhdanova, N.E., Zholkevich, V.N., 
1996. Drought resistance, recovery capacity, and phytohormone content in 
polyploid plum leaves. Russ. J. Plant Physiol. 43 (2), 232–235. 
Parnik, T., Ivanova, H., Keerberg, O., Vardja, R., Niinemets, Ü., 2014. Tree age- 
dependent changes in photosynthetic and respiratory CO2 exchange in leaves of 
micropropagated diploid, triploid and hybrid aspen. Tree Physiol. 34 (6), 585–594. 
https://doi.org/10.1093/treephys/tpu043. 
Ramsey, J., Schemske, D.W., 1998. Pathways, mechanisms, and rates of polyploid 
formation in flowering plants. Annu. Rev. Ecol. Syst. 29 (1), 467–501. https://doi. 
org/10.1146/annurev.ecolsys.29.1.467. 
Ramsey, J., Schemske, D.W., 2002. Neopolyploidy in flowering plants. Annu. Rev. Ecol. 
Syst. 33 (1), 589–639. https://doi.org/10.1146/annurev.ecolsys.33.010802.150437. 
Rao, S., Tian, Y., Xia, X., Li, Y., Chen, J., 2020. Chromosome doubling mediates superior 
drought tolerance in Lycium ruthenicum via abscisic acid signaling. Hortic. Res. 7, 
40. https://doi.org/10.1038/s41438-020-0260-1. 
Rastogi, S., Ohri, D., 2020. Chromosome numbers in Gymnosperms-an update. Silvae 
Genet. 69 (1), 13–19. https://doi.org/10.2478/sg-2020-0003. 
Rice, A., Glick, L., Abadi, S., Einhorn, M., Kopelman, N.M., Salman-Minkov, A., 
Mayzel, J., Chay, O., Mayrose, I., 2015. The Chromosome Counts Database (CCDB) – 
A community resource of plant chromosome numbers. N. Phytol. 206 (1), 19–26. 
https://doi.org/10.1111/NPH.13191. 
Rice, A., Smarda, P., Novosolov, M., Drori, M., Glick, L., Sabath, N., Meiri, S., 
Belmaker, J., Mayrose, I., 2019. The global biogeography of polyploid plants. Nat. 
Ecol. Evol. 3 (2), 265–273. https://doi.org/10.1038/s41559-018-0787-9. 
Riddle, N.C., Kato, A., Birchler, J.A., 2006. Genetic variation for the response to ploidy 
change in Zea mays L. Theor. Appl. Genet. 114, 101–111. https://doi.org/10.1007/ 
s00122-006-0414-z. 
Rieseberg, L.H., 2001. Polyploid evolution: keeping the peace at genomic reunions. Curr. 
Biol. 11 (22), R925–R928. https://doi.org/10.1016/s0960-9822(01)00556-5. 
Rivero, Rodrigo, Emily, B.Sessa, Rosana, Zenil-Ferguson, 2019. ‘EyeChrom and 
CCDBcurator: visualizing chromosome count data from plants’. Appl. Plant Sci. 7 
(1), e01207 https://doi.org/10.1002/aps3.1207. 
Robinson, D.O., Coate, J.E., Singh, A., Hong, L., Bush, M., Doyle, J.J., Roeder, A.H., 
2018. Ploidy and size at multiple scales in the Arabidopsis sepal. Plant Cell 30 (10), 
2308–2329. https://doi.org/10.1105/tpc.18.00344. 
Romero-Aranda, R., Bondada, B.R., Syvertsen, J.P., Grosser, J.W., 1997. Leaf 
characteristics and net gas exchange of diploid and autotetraploid citrus. Ann. Bot. 
79 (2), 153–160. https://doi.org/10.1006/anbo.1996.0326. 
Ruiz, M., Oustric, J., Santini, J., Morillon, R., 2020. Synthetic polyploidy in grafted crops. 
Front. Plant Sci. 11, 1586. https://doi.org/10.3389/FPLS.2020.540894/BIBTEX. 
Ruiz, M., Quinones, A., Martínez-Alcantara, B., Aleza, P., Morillon, R., Navarro, L., 
Primo-Millo, E., Martínez-Cuenca, M.R., 2016b. Effects of salinity on diploid (2x) 
and doubled diploid (4x) Citrus macrophylla genotypes. Sci. Hortic. 207, 33–40. 
https://doi.org/10.1016/j.scienta.2016.05.007. 
Ruiz, M., Quinones, A., Martínez-Cuenca, M.R., Aleza, P., Morillon, R., Navarro, L., 
Primo-Millo, E., Martínez-Alcantara, B., 2016a. Tetraploidy enhances the ability to 
exclude chloride from leaves in carrizo citrange seedlings. J. Plant Physiol. 205, 
1–10. https://doi.org/10.1016/j.jplph.2016.08.002. 
Sattler, M.C., Carvalho, C.R., Clarindo, W.R., 2016. The polyploidy and its key role in 
plant breeding. Planta 243 (2), 281–296. https://doi.org/10.1007/S00425-015- 
2450-X. 
Scholes, D.R., Paige, K.N., 2015. Plasticity in ploidy: a generalized response to stress. 
Trends Plant Sci. 20 (3), 165–175. https://doi.org/10.1016/j.tplants.2014.11.007. 
Selvi, F., Vivona, L., 2022. Polyploidy in Odontarrhena bertolonii (Brassicaceae) in 
relation to seed germination performance and plant phenotype, with taxonomic 
implications. Plant Biosyst. - Int. J. Deal. all Asp. Plant Biol. 156 (4), 959–968. 
https://doi.org/10.1080/11263504.2021.1985001. 
Serapiglia, M.J., Gouker, F.E., Hart, J.F., Unda, F., Mansfield, S.D., Stipanovic, A.J., 
Smart, L.B., 2015. Ploidy level affects important biomass traits of novel shrub Willow 
(Salix) hybrids. Bioenergy. Research 8 (1), 259–269. https://doi.org/10.100 
7/s12155-014-9521-x. 
Serres-Giardi, L., Dufour, J.L., Russell, K., Buret, C., Laurens, F., Santi, F., 2010. Natural 
triploids of wild cherry. Can. J. For. Res. 40, 1951–1961. https://doi.org/10.1139/ 
X10-100. 
A. Ræbild et al.                                                                                                                                                                                                                                 
Forest Ecology and Management 560 (2024) 121767
13
Severns, P.M., Liston, A., 2008. Intraspecific chromosome number variation: a neglected 
threat to the conservation of rare plants. Conserv. Biol. 22 (6), 1641–1647. https:// 
doi.org/10.1111/j.1523-1739.2008.01058.x. 
Shen, C., Li, L., Ouyang, L., Su, M., Guo, K., 2023. E. urophylla  E. grandis high-quality 
genome and comparative genomics provide insights on evolution and diversification 
of eucalyptus. BMC Genom. 24 (1), 223. https://doi.org/10.1186/s12864-023- 
09318-0. 
Shi, Q.H., Liu, P., Liu, M.J., et al., 2015. A novel method for rapid in vivo induction of 
homogeneous polyploids via calluses in a woody fruit tree (Ziziphus jujuba Mill.). 
Plant Cell Tissue Organ Cult. 121, 423–433. https://doi.org/10.1007/s11240-015- 
0713-7. 
Sigurbjornsson, B., Lachance, L.E., 1987. The IAEA and the green revolution. IAEA Bull. 
29 (3), 38–42. 
Silva, A.J., Carvalho, C.R., Clarindo, W.R., 2019. Chromosome set doubling and ploidy 
stability in synthetic auto- and allotetraploid of Eucalyptus: from in vitro condition 
to the field. Plant Cell Tiss. Organ Cult. 138, 387–394. https://doi.org/10.1007/ 
s11240-019-01627-1. 
Simonin, K.A., Roddy, A.B., 2018. Genome downsizing, physiological novelty, and the 
global dominance of flowering plants. PLoS Biol. 16 (1), e2003706. https://doi. 
org//10.1371/journal.pbio.2003706.  
Sivager, G., Calvez, L., Bruyere, S., Boisne-Noc, R., Brat, P., Gros, O., Ollitrault, P., 
Morillon, R., 2021. Specific physiological and anatomical traits associated with 
polyploid and better detoxification processes contribute to improved huanglongbing 
tolerance of the persian lime compared with the mexican lime. Front. Plant Sci. 
1343. https://doi.org/10.3389/fpls.2021.685679. 
Sivager, G., Calvez, L., Heuget, B., Bruyere, S., Boisne-Noc, R.V., Brat, P., Gros, O., 
Ollitraut, P., Morillon, R., 2019. Triploid lime is more tolerant to HLB than diploid 
lime because specific physiological and anatomical traits associated to better 
detoxification processes. Caribbean Science and Innovation Meeting 2019, Oct 2019, 
Pointe-a-Pitre (Guadeloupe), France. hal-02576028. 
Smarda, P., Horova, L., Knapek, O., Dieck, H., Dieck, M., Razna, K., Hrubík, P., Orloci, L., 
Papp, L., Vesela, K., Veselý, P., 2018. Multiple haploids, triploids, and tetraploids 
found in modern-day “living fossil” Ginkgo biloba. Hortic. Res. 5, 55. https://doi. 
org/10.1038/s41438-018-0055-9. 
Smarda, P., Klem, K., Knapek, O., Vesela, B., Vesela, K., Holub, P., Kuchar, V., 
Silerova, A., Horova, L., Bures, P., 2023. Growth, physiology, and stomatal 
parameters of plant polyploids grown under ice age, present-day, and future CO2 
concentrations. N. Phytol. 239 (1), 399–414. https://doi.org/10.1111/nph.18955. 
Soltis, P.S., Marchant, D.B., Van de Peer, Y., Soltis, D.E., 2015. Polyploidy and genome 
evolution in plants. Curr. Opin. Genet. Dev. 35, 119–125. https://doi.org/10.1016/j. 
gde.2015.11.003. 
Syvertsen, J.P., Lee, L.S., Grosser, J.W., 2000. Limitations on growth and net gas 
exchange of diploid and tetraploid Citrus rootstock cultivars grown at elevated CO2. 
J. Am. Soc. Hortic. Sci. 125 (2), 228–234. https://doi.org/10.21273/ 
JASHS.125.2.228. 
Takahashi, F., Kuromori, T., Urano, K., Yamaguchi-Shinozaki, K., Shinozaki, K., 2020. 
Drought stress responses and resistance in plants: from cellular responses to long- 
distance intercellular communication. Front. Plant Sci. 1407. https://doi.org/ 
10.3389/fpls.2020.556972. 
Tamayo-Ordo~nez, M.C., Espinosa-Barrera, L.A., Tamayo-Ordo~nez, Y.J., Ayil- 
Gutierrez, B., Sanchez-Teyer, L.F., 2016. Advances and perspectives in the 
generation of polyploid plant species. Euphytica 209, 1–22. https://doi.org/ 
10.1007/s10681-016-1646-x. 
Tang, Z.Q., Chen, D.L., Song, Z.J., et al., 2010. In vitro induction and identification of 
tetraploid plants of Paulownia tomentosa. Plant Cell Tissue Organ Cult. 102, 213–220. 
https://doi.org/10.1007/s11240-010-9724-6. 
Tate, J.A., Soltis, D.E., Soltis, P.S., 2005. Polyploidy in plants. In: Gregory, T.R. (Ed.), 
Evolution of the Genome. Academic Press,, pp. 371–426. https://doi.org/10.1016/ 
B978-012301463-4/50009-7. ISBN 9780123014634.  
Theroux-Rancourt, G., Roddy, A.B., Earles, J.M., Gilbert, M.E., Zwieniecki, M.A., 
Boyce, C.K., Tholen, D., McElrone, A.J., Simonin, K.A., Brodersen, C.R., 2021. 
Maximum CO2 diffusion inside leaves is limited by the scaling of cell size and 
genome size. Proc. R. Soc. B 288 (1945), 20203145. https://doi.org/10.1101/ 
2020.01.16.904458. 
Tossi, V.E., Martínez Tosar, L.J., Laino, L.E., Lannicelli, J., Regalado, J.J., Escandon, A.S., 
Baroli, I., Causin, H.F., Pitta-Alvarez, S.I., 2022. Impact of polyploidy on plant 
tolerance to abiotic and biotic stresses. Front. Plant Sci. 13, 869423 https://doi.org/ 
10.3389/fpls.2022.869423. 
Touchell, D.H., Palmer, I.E., Ranney, T.G., 2020. In vitro ploidy manipulation for crop 
improvement. Front. Plant Sci. 11, 722. https://doi.org/10.3389/fpls.2020.00722. 
Trojak-Goluch, A., Kawka-Lipinska, M., Wielgusz, K., Praczyk, M., 2021. Polyploidy in 
industrial crops: applications and perspectives in plant breeding. Agronomy 11 (12), 
2574. https://doi.org/10.3390/agronomy11122574. 
Underwood, C.J., Mercier, R., 2022. Engineering apomixis: clonal seeds approaching the 
fields. Annu. Rev. Plant Biol. 73, 201–225. https://doi.org/10.1146/annurev- 
arplant-102720-013958. 
Underwood, C.J., Vijverberg, K., Rigola, D., Okamoto, S., Oplaat, C., Camp, R.H.M.O.D., 
Radoeva, T., Schauer, S.E., Fierens, J., Jansen, K., Mansveld, S., Busscher, M., 
Xiong, W., Datema, E., Nijbroek, K., Blom, E.J., Bicknell, R., Catanach, A., 
Erasmuson, S., Winefield, C., van Tunen, A.J., Prins, M., Schranz, M.E., van Dijk, P. 
J., 2022. A parthenogenesis allele from apomictic dandelion can induce egg cell 
division without fertilization in lettuce. Nat. Genet. 54 (1), 84–93. https://doi.org/ 
10.1038/s41588-021-00984-y. 
Van de Peer, Y., Ashman, T.L., Soltis, P.S., Soltis, D.E., 2021. Polyploidy: An evolutionary 
and ecological force in stressful times. Plant Cell 33 (1), 11–26. https://doi.org/ 
10.1093/PLCELL/KOAA015. 
Van de Peer, Y., Mizrachi, E., Marchal, K., 2017. The evolutionary significance of 
polyploidy, 411-244 Nat. Rev. Genet. 18 (7). https://doi.org/10.1038/nrg.2017.26. 
Vernet, A., Meynard, D., Lian, Q., Mieulet, D., Gibert, O., Bissah, M., Rivallan, R., 
Autran, D., Leblanc, O., Meunier, A.C., Frouin, J., Taillebois, J., Shankle, K., 
Khanday, I., Mercier, R., Sundaresan, V., Guiderdoni, E., 2022. High-frequency 
synthetic apomixis in hybrid rice. Nat. Commun. 13 (1), 7963. https://doi.org/ 
10.1038/s41467-022-35679-3. 
Verslues, P.E., 2016. ABA and cytokinins: challenge and opportunity for plant stress 
research. Plant Mol. Biol. 91 (6), 629–640. https://doi.org/10.1007/s11103-016- 
0458-7. 
Veselý, P., Smarda, P., Bures, P., Stirton, C., Muasya, A.M., Mucina, L., Horova, L., 
Vesela, K., Silerova, A., Smerda, J., Knapek, O., 2020. Environmental pressures on 
stomatal size may drive plant genome size evolution: evidence from a natural 
experiment with Cape geophytes. Ann. Bot. 126 (2), 323–330. https://doi.org/ 
10.1093/aob/mcaa095. 
Vít, P., Douda, J., Krak, K., Havrdova, A., Mandak, B., 2017. Two new polyploid species 
closely related to Alnus glutinosa in Europe and North Africa – an analysis based on 
morphometry, karyology, flow cytometry and microsatellites. Taxon 66, 567–583. 
https://doi.org/10.12705/663.4. 
Walters, S.M., 1964. Betulaceae. In: Tutin, T.G., Heywood, V.H., Burges, N.A., 
Valentine, D.H., Walters, S.M., Webb, D.A. (Eds.), Flora Europaea 1. Cambridge 
University Press,, Cambridge, pp. 57–59. 
Wang, Z., Fan, G., Dong, Y., Zhai, X., Deng, M., Zhao, Z., Liu, W., Cao, Y., 2017b. 
Implications of polyploidy events on the phenotype, microstructure, and proteome of 
Paulownia australis. PLOS One 12 (3), e0172633. https://doi.org/10.1371/ 
JOURNAL.PONE.0172633. 
Wang, N., McAllister, H.A., Bartlett, P.R., Buggs, R.J.A., 2016. Molecular phylogeny and 
genome size evolution of the genus Betula (Betulaceae). Ann. Bot. 117, 1023–1035. 
https://doi.org/10.1093/aob/mcw048. 
Wang, X., Morton, J.A., Pellicer, J., Leitch, I.J., Leitch, A.R., 2021. Genome downsizing 
after polyploidy: mechanisms, rates and selection pressures. Plant J. 107 (4), 
1003–1015. https://doi.org/10.1111/tpj.15363. 
Wang, X., Xu, Y., Zhang, S., Cao, L., Huang, Y., Cheng, J., Wu, G., Tian, S., Chen, C., 
Liu, Y., Yu, H., Yang, X., Lan, H., Wang, N., Wang, L., Xu, J., Jiang, X., Xie, Z., 
Tan, M., Larkin, R.M., Chen, L.-L., Ma, B.-G., Ruan, Y., Deng, X., Xu, Q., 2017a. 
Genomic analyses of primitive, wild and cultivated citrus provide insights into 
asexual reproduction. Nat. Genet. 49, 765–772. https://doi.org/10.1038/ng.3839. 
Williams, J.H., Oliveira, P.E., 2020. For things to stay the same, things must change: 
polyploidy and pollen tube growth rates. Ann. Bot. 125 (6), 925–935. https://doi. 
org/10.1093/aob/mcaa007. 
Wilson, M.J., Fradera-Soler, M., Summers, R., Sturrock, C.J., Fleming, A.J., 2021. Ploidy 
influences wheat mesophyll cell geometry, packing and leaf function. Plant Direct 5 
(4), e00314. https://doi.org/10.1002/pld3.314. 
Wood, T.E., Takebayashi, N., Barker, M.S., Mayrose, I., Greenspoon, P.B., Rieseberg, L. 
H., 2009. The frequency of polyploid speciation in vascular plants. Proc. Natl. Acad. 
Sci. USA 106 (33), 13875–13879 https://doi.org/10/fg95hm.  
Wouters, M., Corneillie, S., Dewitte, A., Van Doorsselaere, J., Van den Bulcke, J., Van 
Acker, J., Vanholme, B., Boerjan, W., 2022. Whole genome duplication of wild-type 
and CINNAMYL ALCOHOL DEHYDROGENASE1-downregulated hybrid poplar 
reduces biomass yield and causes a brittle apex phenotype in field-grown wild types. 
Front. Plant Sci. 13, 995402. https://doi.org/10.3389/fpls.2022.995402.  
Wu, J., Cheng, X., Kong, B., et al., 2022. In vitro octaploid induction of Populus 
hopeiensis with colchicine. BMC Plant Biol. 22, 176. https://doi.org/10.1186/ 
s12870-022-03571-3. 
Wu, J., Sang, Y., Zhou, Q., Zhang, P., 2020. Colchicine in vitro tetraploid induction of 
Populus hopeiensis from leaf blades. Plant Cell, Tissue Organ Cult. (PCTOC) 141, 
339–349. https://doi.org/10.1007/s11240-020-01790-w. 
Wu, J.H., Ferguson, A.R., Murray, B.G., Jia, Y., Datson, P.M., Zhang, J., 2012. Induced 
polyploidy dramatically increases the size and alters the shape of fruit in Actinidia 
chinensis. Ann. Bot. 109, 169–179. https://doi.org/10.1093/aob/mcr256. 
Xiong, D., Huang, J., Peng, S., Li, Y., 2017. A few enlarged chloroplasts are less efficient 
in photosynthesis than a large population of small chloroplasts in Arabidopsis 
thaliana. Sci. Rep. 7, 5782. https://doi.org/10.1038/s41598-017-06460-0. 
Xu, E., Fan, G., Niu, S., Zhao, Z., Deng, M., Dong, Y., 2015. Transcriptome sequencing 
and comparative analysis of diploid and autotetraploid Paulownia australis. Tree 
Genet. Genomes 11, 1–13. https://doi.org/10.1007/s11295-014-0828-8. 
Xu, T., Zhang, S., Du, K., Yang, J., Kang, X., 2022. Insights into the molecular regulation 
of lignin content in triploid poplar leaves. Int. J. Mol. Sci. 23, 4603. https://doi.org/ 
10.3390/ijms23094603. 
Xue, H., Zhang, B., Tian, J.R., Chen, M.M., Zhang, Y.Y., Zhang, Z.H., Ma, Y., 2017. 
Comparison of the morphology, growth and development of diploid and 
autotetraploid ‘Hanfu’ apple trees. Sci. Hortic. 225, 277–285. https://doi.org/ 
10.1016/j.scienta.2017.06.059. 
Yadav, C.B., Rozen, A., Eshed, R., Ish-Shalom, M., Faigenboim, A., Dillon, N., Bally, I., 
Webb, M., Kuhn, D., Ophir, R., Cohen, Y., Sherman, A., 2023. Promoter insertion 
leads to polyembryony in mango - a case of convergent evolution with citrus. Hortic. 
Res. 10 (12) https://doi.org/10.1093/hr/uhad227. 
Yang, J., Wang, J., Liu, Z., Xiong, T., Lan, J., Han, Q., Li, Y., Kang, X., 2018. Megaspore 
chromosome doubling in Eucalyptus urophylla S.T. Blake induced by colchicine 
treatment to produce triploids. Forests 9 (11), 728. https://doi.org/10.3390/ 
f9110728. 
Yao, C., Pu, J., 1998. Timber characteristics and pulp properties of the triploid of Populus 
tomentosa. J. Beijing For. Univ. 20 (5), 18–21. 
Yirga, M., 2021. Polyploidy and its implications in plants breeding – a review. Int. J. 
Curr. Res. Biosci. Plant Biol. 8 (3), 1–9. https://doi.org/10.20546/ 
ijcrbp.2021.803.001. 
A. Ræbild et al.                                                                                                                                                                                                                                 
Forest Ecology and Management 560 (2024) 121767
14
Yoo, M.J., Szadkowski, E., Wendel, J.F., 2013. Homoeolog expression bias and 
expression level dominance in allopolyploid cotton. Heredity 110 (2), 171–180. 
https://doi.org/10.1038/HDY.2012.94. 
Yu, D., Gu, X., Zhang, S., Dong, S., Miao, H., Gebretsadik, K., Bo, K., 2021. Molecular 
basis of heterosis and related breeding strategies reveal its importance in vegetable 
breeding. Hortic. Res. 8, 120. https://doi.org/10.1038/s41438-021-00552-9. 
Zhang, J., Song, X., Zhang, L., et al., 2019. Agronomic performance of 27 Populus clones 
evaluated after two 3-year coppice rotations in Henan. China GCB-BioEnergy 12 (2), 
168–181. https://doi.org/10.1111/gcbb.12662. 
Zhang, P., Wu, F., Kang, X., 2012. Genotypic variation in wood properties and growth 
traits of triploid hybrid clones of Populus tomentosa at three clonal trials. Tree 
Genet. Genomes 8 (5), 1041–1050. https://doi.org/10.1007/s11295-012-0484-9. 
Zhang, P., Wu, F., Kang, X., 2013. Genetic control of fiber properties and growth in 
triploid hybrid clones of Populus tomentosa. Scand. J. For. Res. 28 (7), 621–630. 
https://doi.org/10.1080/02827581.2013.829868. 
Zhang, W.W., Song, J., Wang, M., Liu, Y.Y., Li, N., Zhang, Y.J., Holbrook, N.M., Hao, G. 
Y., 2017. Divergences in hydraulic architecture form an important basis for niche 
differentiation between diploid and polyploid Betula species in NE China. Tree 
Physiol. 37 (5), 604–616. https://doi.org/10.1093/treephys/tpx004. 
Zhang, F., Xue, H., Lu, X., Zhang, B., Wang, F., Ma, Y., Zhang, Z., 2015. 
Autotetraploidization enhances drought stress tolerance in two apple cultivars. Trees 
29 (6), 1773–1780. https://doi.org/10.1007/s00468-015-1258-4. 
Zhang, Y., Wang, B., Qi, S., Dong, M., Wang, Z., Li, Y., Chen, S., Li, B., Zhang, J., 2019a. 
Ploidy and hybridity effects on leaf size, cell size and related genes expression in 
triploids, diploids and their parents in Populus. Planta 249, 635–646. https://doi. 
org/10.1007/s00425-018-3029-0. 
Zhao, X., Li, Y., Zheng, M., et al., 2015. Comparative analysis of growth and 
photosynthetic characteristics of (Populus simonii  P. nigra)  (P. nigra  P. 
simonii) hybrid clones of different ploidies. PLOS One 10 (4), e0119259. https://doi. 
org/10.1371/journal.pone.0119259. 
Zhao, Z., Li, Y., Liu, H., Zhai, X., Deng, M., Dong, Y., Fan, G., 2017. Genome-wide 
expression analysis of salt-stressed diploid and autotetraploid Paulownia tomentosa. 
PLOS One 12 (10), e0185455. https://doi.org/10.1371/journal.pone.0185455. 
Zhi-qing, F.G.Q.Y., 2006. Autotetraploid induction of Paulownia elongata with 
colchione. J. Nucl. Agric. Sci. 20 (06), 473. 
Zhu, T., Wang, L., You, F.M., Rodriguez, J.C., Deal, K.R., Chen, L., Li, J., Chakraborty, S., 
Balan, B., Jiang, C.Z., Brown, P.J., 2019. Sequencing a Juglans regia  J. microcarpa 
hybrid yields high-quality genome assemblies of parental species. Hortic. Res. 6, 55. 
https://doi.org/10.1038/s41438-019-0139-1. 
A. Ræbild et al.