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Author(s): Johanna Riikonen, Hanna Ruhanen, Anne Uimari, Marja Poteri, Anna Toljamo, Harri 
Kokko, James D. Blande, Raija Kumpula, Minna Kivimäenpää 
Title: Impact of pre-harvest UVC treatment on powdery mildew infection and strawberry 
quality in tunnel production in Nordic conditions 
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: 
Johanna Riikonen, Hanna Ruhanen, Anne Uimari, Marja Poteri, Anna Toljamo, Harri Kokko, James D. 
Blande, Raija Kumpula, Minna Kivimäenpää, Impact of pre-harvest UVC treatment on powdery mildew 
infection and strawberry quality in tunnel production in Nordic conditions, Scientia Horticulturae, 
Volume 338, 2024, 113706, ISSN 0304-4238, https://doi.org/10.1016/j.scienta.2024.113706 
Research Paper
Impact of pre-harvest UVC treatment on powdery mildew infection and
strawberry quality in tunnel production in Nordic conditions
Johanna Riikonen a,*, Hanna Ruhanen a, Anne Uimari a, Marja Poteri a, Anna Toljamo b,
Harri Kokko b, James D. Blande b, Raija Kumpula c, Minna Kivimaenpaa a
a Natural Resources Institute Finland, Juntintie 154, Suonenjoki FI-77600, Finland
b Department of Environmental and Biological Sciences, University of Eastern Finland, P.O. Box 1627, Kuopio FI-70211, Finland
c Regional Development Company SavoGrow, Jalkalantie 6, Suonenjoki FI-77600, Finland
A R T I C L E I N F O
Keywords:
Fruit quality
Phytopathology
Powdery mildew
Preharvest
Strawberry
Tunnel cultivation
UVC radiation
A B S T R A C T
Preharvest UVC radiation treatment has emerged as a promising alternative to chemical plant protection
methods in plant production systems for preventing fungal diseases. In our study, three strawberry (Fragaria x
ananassa) cultivars were subjected to nightly UVC treatment (20 s, 0.02 kJ/m2) delivered through LED tech-
nology (with a peak at 276 nm) within polytunnel conditions in Central Finland. The aim was to evaluate the
effectiveness of the UVC treatment in inhibiting powdery mildew (caused by Podosphaera spp.), as well as to
assess its impact on crop yield, fruit quality, firmness, volatile organic compound (VOC) profile, and leaf
properties across two consecutive growing seasons. The UVC treatment successfully suppressed the growth of
powdery mildew in all three tested strawberry cultivars throughout the experiment, without causing any visible
damage to the leaves. The UVC treatment led to an increase in the crop yield of marketable fruits without
affecting their size. The impact on fruit quality varied, depending on the specific cultivar, sampling time, and the
year under consideration. Fruit firmness following 2–3 days of refrigeration improved due to the UVC treatment.
Our findings suggest that UVC treatment can alter the fruit’s VOC profile, either directly or indirectly through
disease management, affecting its aroma. These findings emphasize the diverse advantages of UVC treatment in
enhancing disease resistance and enhancing specific fruit attributes. This suggests the potential for integration of
UVC treatment into plant production systems, particularly in tunnel cultivation within Nordic conditions, as a
promising approach to improve overall crop management strategies.
1. Introduction
Powdery mildew is a plant disease caused by almost 900 fungal
species from 19 genera of Ascomycota. It is considered one of the most
economically damaging diseases in plant production systems worldwide
(Kusch et al., 2023). The prevailing method for managing powdery
mildew is the application of fungicides. Regrettably, the frequent use of
fungicides is not only costly but also has adverse effects on the envi-
ronment and human health and contributes to the development of
pathogen resistance (Komarek et al., 2010; Oliveira et al., 2017).
UVC radiation is well-known for its germicidal properties and its
ability to damage the DNA and cellular structures of pathogens (Urban
et al., 2016). Recent research has suggested that UVC radiation can be
harnessed to effectively suppress the growth and proliferation of
Podosphaera aphanis, the causative agent of powdery mildew on growing
strawberry plants (Urban et al., 2016; Peng et al., 2022). Pre-harvest
UVC treatment in strawberry production has been explored and
employed in various locations around the world as a potential method to
control diseases, improve fruit quality, and extend shelf life (Urban
et al., 2016; Peng et al., 2022). It has been found that several fungal
pathogens can be effectively controlled by exposing the plants to low
doses of UVC irradiation, if followed by a period of darkness
(Janisiewicz et al., 2016; Suthaparan et al., 2017; Takeda et al., 2019;
Pathak et al., 2020).
The effects of UVC radiation on strawberry plants are highly
dependent on the dosage, duration, and timing of exposure, which are
* Corresponding author.
E-mail addresses: johanna.riikonen@luke.fi (J. Riikonen), hanna.ruhanen@luke.fi (H. Ruhanen), ext.anne.uimari@luke.fi (A. Uimari), poterinmarja@gmail.com
(M. Poteri), anna.toljamo@uef.fi (A. Toljamo), harri.kokko@uef.fi (H. Kokko), james.blande@uef.fi (J.D. Blande), raija.kumpula@savogrow.fi (R. Kumpula), minna.
kivimaenpaa@luke.fi (M. Kivimaenpaa).
Contents lists available at ScienceDirect
Scientia Horticulturae
journal homepage: www.elsevier.com/locate/scihorti
https://doi.org/10.1016/j.scienta.2024.113706
Received 7 February 2024; Received in revised form 7 June 2024; Accepted 30 September 2024
Scientia Horticulturae 338 (2024) 113706 
Available online 10 October 2024 0304-4238/© 2024 Natural Resources Institute Finland. Published by Elsevier B.V. This is an open access article under the CC BY license 
( http://creativecommons.org/licenses/by/4.0/ ). 
crucial to achieving desired outcomes while minimizing potential
negative effects. When plants are exposed to UVC radiation at high in-
tensity and duration, it causes disturbances in cell metabolism, such as
damage in DNA, proteins, and membranes, and consequently, reduces
photosynthesis, growth, and vigor of plants (Urban et al., 2016). Low
UVC doses, in turn, may trigger plant defense responses, such as acti-
vation of the antioxidant system and the synthesis of phenolic com-
pounds, resulting in higher stress tolerance (de Oliveira et al., 2016;
Severo et al., 2017; Xu et al., 2019). Pre- and postharvest UVC treatment
has also been utilized for extending the shelf life of the fruits (Pombo
et al., 2011; Xie et al., 2015; 2016). The potential enhancement in
phenolic compounds, anthocyanins, and antioxidants holds promise for
improving both pathogen resistance and fruit quality across various fruit
species (Urban et al., 2016).
The impact of UVC on volatile phytochemicals remains relatively
unclear. The volatile compounds of strawberries encompass a range of
elements, including esters, alcohols, aldehydes, ketones, acids, terpene
compounds, furanones, and lactones, all of which significantly
contribute to the fragrance and aroma of strawberries (Nuzzi et al.,
2008; Zamorska, 2022). Moreover, these volatile compounds play a
crucial role in defending against biotic stress in various parts of the
strawberry plant, such as leaves, flowers, and fruits (Amil-Ruiz et al.,
2011).
The polytunnel production of strawberries is experiencing a notable
surge in popularity across the Nordic countries, driven by the region’s
challenging climate, characterized by short growing seasons and un-
predictable weather patterns (Sønsteby and Karhu, 2005). However,
powdery mildew poses a significant challenge in strawberry tunnel
cultivation, where the climate and environmental conditions can favor
the development of the pathogens. At northern latitudes, flowering and
fruit development often occurs in June and July when there is typically a
period of twilight or "white nights" rather than complete darkness. In
central Finland sunrise occurs at 3am., and at 1am the radiation may be
10–20 W/m2 (maximum radiation during daytime about 950 W/m2).
Consequently, it’s crucial to assess the efficacy of the UVC method,
which necessitates a dark period post-treatment, under northern
conditions.
Functionality of UVC radiation in preventing fungal diseases in
strawberry has been proven in growth chambers (Xu et al. 2017; Sun
et al. 2020), greenhouse (Van Hemelrijck et al., 2010; Van Delm et al.,
2014; Xie et al., 2016; Forges et al., 2020) and open field (Onofre et al.,
2021; Takeda et al., 2021) experiments. To our knowledge, the study
presented in this paper is one of the few experiments where impacts of
UVC radiation on strawberry crop yield, fruit quality and leaf properties
have been studied under tunnel conditions (Janisiewicz et al., 2016;
Takeda et al., 2019), employing the LED technique.
The aim of the experiment was to explore the impacts of nightly UVC
treatment on (1) effectiveness at suppressing powdery mildew in three
strawberry cultivars, (2) crop yield, (3) fruit quality, (4) VOC profile of
the fruits, and (5) physiological properties of the leaves.
2. Materials and methods
2.1. Experimental set up
The experiment took place in a strawberry tunnel located in Suo-
nenjoki, Finland (6239′N, 2703′E, 142 m above sea level). Two sepa-
rate experiments were conducted. In 2021, June-bearing strawberry
cultivars ’Malling Centenary’ and ’Limalexia’ were used, while in 2022,
’Malling Centenary’ and ’Sonsation’ were the chosen varieties. As our
aim was to investigate both annual variation in plant responses to UVC
radiation and differences in the responses of different strawberry culti-
vars, we chose to use ’Malling centenary’ in both years and to vary the
other cultivar. All cultivars used in the experiments are commonly used
in tunnel production in Finland. The frigo plants were sourced from the
Netherlands, gradually thawed in a chilled storage facility, and
subsequently transplanted into the strawberry tunnel in table-tops.
Planting occurred on 15 June 2021, and 1 June 2022.
The plants were arranged in a zigzag pattern, with four plants per
container (20 cm  50 cm) containing coconut substrate. Nutrient
fertilization was carried out using a nutrient solution composed of Krista
K, Calcinit, and Ferticare (7-9-32) (Yara, Vilna, Lithuania). Drip irriga-
tion, consisting of two drippers per container, was employed according
to the climatic requirements. Runners were removed weekly.
The experiment included two rows of strawberry plants arranged
within the tunnel. One row received nightly UV radiation treatment,
while the other row served as the control group. These rows were situ-
ated on opposite sides of the tunnel and were separated by a plastic
partition. The distance between the rows was approximately 4 m. In the
second year of the experiment, the placement of the treatments was
switched to mitigate the influence of microclimate variations inside the
tunnel. Each row comprised 16 containers of ’Malling Centenary’ plants
in both 2021 and 2022, along with 15 containers of ’Limalexia’ (in
2021) or ’Sonsation’ (in 2022). This resulted in a total of 60 to 64 plants
per cultivar per treatment. The cultivars were arranged sequentially in
the rows, and the rows themselves were divided into four blocks, each
containing four containers of each cultivar. Air temperature inside the
tunnel was recorded with Hobo loggers (Fig. 1). Upon development of
flower buds (starting at the end of June) two bumblebee (Bombus ter-
restris) boxes (Agrobio, Almería, Spain) were installed in the tunnel for
Fig. 1. The air temperature inside the strawberry tunnel was recorded during
experiments conducted in 2021 and 2022 in Central Finland. Planting was
performed on 15 June 2021 and 1 June 2022. Flowering began in early July,
and the first symptoms of powdery mildew were observed after mid-July in
both years. Daily mean values were calculated from hourly measurements.
Fig. 2. LED-based UV-exposure equipment developed for research purposes in
Suonenjoki, Finland.
J. Riikonen et al. Scientia Horticulturae 338 (2024) 113706 
2 
pollination.
In both years, the remaining half of the tunnel was utilized for
growing strawberry plants for various purposes, creating a high disease
pressure environment. Natural powdery mildew infection symptoms
were first observed in mid-July in both years, with a stronger occurrence
in the 2021 growing season.
2.2. UV exposure
UVC exposure was conducted nightly with a custom-built apparatus
designed for research purposes (Fig. 2). UV LED chips (peaking at 276
nm, Shenzhen Hanhua Opto Co., Ltd., Shenzhen, China) were embedded
within a semicylindrical metal structure measuring 68 cm in width, 50
cm in height (ELSOR, Suonenjoki, Finland). The apparatus was posi-
tioned so that the LEDs were approximately 10 cm above the plant
canopy, and the LED panel was raised as the plants grew during the
growing season to ensure a consistent UV dosage. The automated
apparatus moved along metal poles situated above the plants (Fig. 2),
making intermittent stops above each container to subject the plants to
20 s of UV radiation. This exposure regimen extended from planting
until the conclusion of the experiment in mid-September.
Each night, the UVC dosage delivered to each container was 0.02 kJ
m 2, resulting in a cumulative total of 1.54 and 1.82 kJ m 2 during the
growing seasons 2021 and 2022, respectively. A similar apparatus,
lacking UV LEDs, was deployed, and operated above the control row.
These devices were in operation every night from 11:00PM to 11:15PM.
The intensity and duration of UVC exposure were determined through
preliminary tests on Botrytis cinerea cultivated in Petri dishes, as well as a
pre-experiment conducted during the 2020 growing season using the
same UVC device (unpublished results). The spectral distribution of light
was measured using a spectroradiometer (AvaSpec-ULS2048 Starline,
Avantes BV, Apeldoorn, The Netherlands, Fig. 3). The UVC radiation
dose was measured using a digital UVC radiometer (RM-22, Opsytec Dr.
Grobel GmbH, Ettlingen, Germany) located in the central part of the
irradiation zone. The LEDs also emitted radiation within the UVB range,
accounting for 41 % of the energy output.
2.3. Fruit harvesting
Fruit harvesting occurred at regular intervals, typically every three
to four days, spanning the entire cropping period. In 2021, this period
extended from 19 July to 2 September, while in 2022, it ranged from 14
July to 31 August. In 2021, fruits were classified into two groups:
marketable and low quality (identified by a diameter of < 18 mm,
malformation, mold, mechanical damage, or powdery mildew infec-
tion). In 2022, an extra category was created for fruits affected specif-
ically by powdery mildew. For each category, measurements were taken
for fresh mass and the number of fruits. These data were then used to
calculate the yield per individual plant, and an average fruit size.
2.4. Determination of Brix, acidity, total phenolics, and total
anthocyanins
Sampling to assess fruit chemical properties, including total soluble
solid content (Brix), acidity, total phenols, and total anthocyanins, was
conducted biannually. For ’Malling Centenary’, the samplings took
place on 19 July and 2 August 2021, and on 14 July and 28 July 2022. In
the case of ’Limalexia’, the sampling occurred on 29 July and 9 August
2021, while for ’Sonsation’, it was on 18 July and 28 July 2022.
Approximately four to five mature fruits were selected from each
container for analysis and frozen immediately after sampling.
Frozen fruits were defrosted in a microwave oven using the defrost
setting and subsequently homogenized for 3 min with a centrifugal
juicer. From this homogenized mixture, two-milliliter subsamples of
juice were extracted, then centrifuged at 16,100 g for 5 min before being
utilized for further analysis.
Brix values were determined using the juice, while acidity was
measured from a 1:50 dilution of the juice, employing a Pocket Brix-
acidity meter, PAL-BX|ACID F5, manufactured by ATAGO CO., LTD,
Japan.
The total phenolic content was assessed through the Folin-Ciocalteu
method, as described by Singleton and Rossi (1965). Two technical
replicates were conducted for each sample. The juice was diluted at a
ratio of 1:40 with distilled water, and 200 µl of this dilution was com-
bined with 1 ml of a 10 % Folin-Ciocalteu reagent. Subsequently, 800 µl
of a 7.5 % sodium carbonate solution was added, and the mixture was
thoroughly vortexed. After an incubation period of 120 min in the dark
at room temperature, the samples were mixed once more, and 200 µl
subsamples were pipetted into a 96-well plate.
Absorbances at 765 nm were determined using a VICTOR3 1420
multilabel plate reader (PerkinElmer, Inc., the United States). Total
phenolic concentrations were quantified utilizing a gallic acid standard
curve, and the results are expressed as milligrams of gallic acid equiv-
alents (GAE) per 100 ml of juice (mg GAE / 100 ml juice).
The total anthocyanin content was determined using the pH differ-
ential method outlined by Lee et al. (2005). Two technical replicates
were performed for each sample. To prepare the samples, dilutions
(1:20) of the juice were made in pH 1 and pH 4.5 buffers, and their
absorbances were measured at 510 nm and 700 nm using a spectro-
photometer within a 20 to 50 min time frame.
To calculate the concentrations of total anthocyanins, the molar
absorption coefficient (Ɛ ˆ 15,600 M-1cm 1) and the molecular weight
(MW ˆ 433.4 g mol-1) of pelargonidin-3-glucoside (P3g) were
employed. P3g is the primary anthocyanin identified in strawberries, as
documented by Tonutare et al. (2014). The results are expressed as
milligrams of P3g equivalents per 100 ml of juice (mg P3gE / 100 ml
juice).
2.5. Ascorbic acid concentration
Five mature fruits were collected for total ascorbic acid analyses
from each container on 25 July 2022. The analysis of ascorbic acid was
performed using the Megazyme Ascorbic Acid Assay Kit (L-Ascorbate)
(K-ASCO) and absorbance was measured at 578 nm with a well plate
reader (FLUOstar Omega, BMG Labtech GmbH, Germany) following the
kit instructions. To determine the total ascorbic acid content, dehy-
droascorbic acid was converted into ascorbic acid by adding DTT to the
sample at a final concentration of 1 mM and incubating the mixture for
10 min.
2.6. Fruit firmness
Fruit firmness assessments were conducted using a penetrometer (T.
Fig. 3. Spectral composition of UV radiation used for the experiments.
J. Riikonen et al. Scientia Horticulturae 338 (2024) 113706 
3 
R. Turoni srl, Forli, Italy) equipped with a ‘star’ plunger specifically
designed for strawberries (model 53207, Turoni, Forlì, Italy). Five
strawberries from each container were collected on 18 July (’Malling
centenary’) and on 22 July 2022 (’Sonsation’) and stored in cool boxes
(five strawberries/box). These boxes were refrigerated at‡8 C until the
strawberries’ firmness was evaluated after two days for Malling cente-
nary and three days for ’Sonsation’. The fruits were halved longitudi-
nally and the penetrometer measurements were taken at the thickest
part of each half. The results were recorded in grams.
2.7. VOC analyses
The analysis of volatile organic compounds (VOCs) from fruit sam-
ples was conducted on 4 August 2022, to assess the impact of P. aphanis
infection and UVC-treatment on emissions, as well as to characterize the
volatile profiles of ’Malling Centenary’ and ’Sonsation’ cultivars under
UVC and control conditions. Three fully ripe fruits, exhibiting typical
visual characteristics, were sampled from six systematically selected
containers within the rows of the tunnel for each cultivar and treatment
combination. Subsequently, these collected fruits were placed into cool
boxes and transported to the University of Eastern Finland in Kuopio on
the same day for the VOC analysis.
The severity of P. aphanis infection was classified using the following
criteria: no visible infection (0), initial symptoms of infection in one or
two seeds (1), and clear infection covering 20–80 % of the surface area
(2). Additionally, the fresh mass of the fruits was recorded during the
sampling process (Table S1).
VOC collection was conducted under laboratory conditions using a
bench-based dynamic headspace sampling system with six sampling
lines. The bench temperature was 20–22 C. The fruits were placed in 1 L
glass jars that had been cleaned with water and ethanol and baked in an
incubator at 120 C to remove impurities. Purified inlet air was gener-
ated with a zero-air generator (Aadco Instruments, 747-30, Cleves, OH,
USA), humidified and introduced via Teflon tubing into the jars at
approx. 325 ml min 1. The jars were flushed for 5 min and then VOCs
were collected from an outlet port for 30 min into Stainless steel tubes
filled with 200 mg of Tenax TA adsorbent (Markes International Ltd.,
Llantrisant, UK) at a flow rate of approx. 225 ml min 1. Air was pulled
through the Stainless-steel tubes with a vacuum pump (D-79112, KNF,
Germany) connected via Silicone tubing. A blank sample was collected
using the same method, but with an empty jar. Inlet and outlet air flows
were calibrated with a mini-Buck calibrator (AP Buck Inc., Orlando, FL,
USA).
VOC analysis was performed by gas chromatography-mass spec-
trometry (GC–MS) (Agilent 7890A GC and 5975C VL MSD; New York,
USA). Trapped compounds were desorbed with a thermal desorption
unit (TD-100; Markes International Ltd.) at 300 C for 10 min and then
cryofocused at  10 C. The compounds were transferred in split mode to
an HP-5MS UI capillary column (60 m  0.25 mm; film thickness 0.25
μm) with helium as a carrier gas. The oven temperature was held at 40
C for 1 min, then programmed to increase by 5 C min 1 to 125 C and
then by 10 Cmin 1 to 260 C with a column flow of 1.2 ml min 1. Mass
spectra were obtained by scanning from 33 to 400 m z 1.
Compounds were identified and quantified with help of MSD
Chemstation Data Analysis software (Agilent) andWiley275 and NIST20
databases. Authentic standards were available for linalool, cis-3-hexenol
Fig. 4. Cumulative yield of marketable (UVC-treated white circles, controls black circles) and non-marketable (UVC-treated white triangles, controls black triangles)
yield (SE) in strawberry cultivars ’Malling centenary’ (b) and ’Limalexia’ (b) grown in a tunnel in growing seasons 2021, and marketable and powdery mildew
infected fruits in ’Malling centenary’ (c) and ’Sonsation’ (d) in 2022. Statistically significant differences between the UVC-treated and control plants are indicated
by asterisks.
J. Riikonen et al. Scientia Horticulturae 338 (2024) 113706 
4 
and methylsalicylate. α-Humulene was used for quantifying sesquiter-
penes, cis-3-hexenol for alcohols, aldehydes, acids and ketones and cis-
3-hexenyl isobutyrate for esters and other compounds. Quantification
was based on Total Ion Counts (TIC). Emissions from blanks were sub-
tracted from fruit emissions. Emission rates were calculated as follows:
EˆFx…C2  C1†=m
where E is Emission rate (ng g 1 (FW) h 1), F is the flow rate to the
collection chamber (L min 1), C2 is the concentration of the outgoing air
(ng L 1), C1 is the concentration of the incoming air (ng L 1), m is the
berries’ FW (g). C1 was considered to be 0 because the incoming air was
filtered, and the quantities of VOCs determined from blank samples were
subtracted from the fruit emissions.
2.8. Leaf measurements
Symptoms of powdery mildew in leaves were scored on 2 August and
8 August 2022 according to scale modified from Simpson (1987), where
scores denote: (0) a healthy plant with no visible disease symptoms, (1)
slight leaf curling with no visible mycelium, (2) leaf curling and
mottling, (3) severe leaf curling, redding and visible damage to lower
leaf surface and (4) severe necrosis and some leaf death.
A Dualex fluorimeter Dualex® Scientific (Force-A, Orsay, France)
was used to measure chlorophyll, epidermal flavonol and nitrogen bal-
ance (NBI, calculated as chlorophyll/flavonols, describing leaf nitrogen
status) indexes. The measurements were made from the two youngest
mature, visibly intact leaflets from each plant on 2 August 2022.
Leaf samples for assessing dry matter content were gathered on 8
September 2022, with two leaflets collected from each plant. The fresh
mass (FM) and dry mass (DM) of these leaflets were recorded, and an
average value was computed for each container.
Following the FW measurements, leaflets were scanned using a
flatbed scanner (Epson Perfection V700Photo). The areas of both the
leaflets and any holes in them were quantified using the tools available
in ImageJ 1.53c. Subsequently, the leaflets were subjected to drying at a
constant temperature of ‡60 C. Specific leaf area (SLA) was calculated
by dividing the leaf area by the dry mass. Additionally, the dry mass
content of the leaves and the area of feeding damage (holes) were
determined.
2.9. Statistical analyses
The analysis of marketable and non-marketable fruit yield data uti-
lized Linear Mixed Models ANOVA, with sampling time, cultivar, and
treatment designated as fixed factors. Random factors used in the
analysis were treatment and container, while blocks were considered as
subjects to acknowledge the interdependence of measured treatments
and containers across multiple samplings. Data-analyses of fruit chem-
ical properties were carried out individually for each sampling date.
Non-significant random factors were removed from the model. Subse-
quent examination of interactions was conducted using the Sidak test.
Principal Component Analysis (PCA) was initially employed to
delineate variances in cultivar volatile profiles (Supplementary infor-
mation). Subsequently, separate PCA analyses were conducted for each
cultivar to explore distinctions between treatments or P. aphanis infec-
tion. To delve deeper into the effects of cultivar, treatment, and
P. aphanis infection class on the volatile blend, T-tests of PC scores were
executed. To streamline the analysis, for ’Malling centenary’, infection
classes 1 and 2 were amalgamated due to the limited samples in class 2
(Table S1). In the case of ’Sonsation’, infection classes were amalgam-
ated in two ways: distinguishing between no infection (0) versus any
infection (1 and 2), and a separate comparison between severely infec-
ted (2) versus others (0 and 1). PCA was conducted using Simca 17.0.1,
while all other analyses were performed using SPSS 29.0. A significance
level of P < 0.05 was adopted for determining statistical significance.
3. Results
3.1. Fruit production and crop yield
In both years, the cumulative yield of marketable fruits from the
UVC-treated plants was significantly higher, and the yield of non-
marketable fruits lower than those from the control plants (Fig. 4). In
2021, the total yield of fruits was equivalent in both treatments. How-
ever, in ’Sonsation’ in 2022, there was a slight decrease in the total yield
in the UVC-treated plants compared to the controls (Table 1). The
average size of the fruits was not affected by the treatments (Table 1).
The cumulative yield of non-marketable fruits in control plants started
to exceed that from the UVC plants between late July and early August,
soon after the first symptoms of powdery mildew were detected in the
canopy on 23 July 2021 and on 27 July 2022. In 2022, the total fresh
mass of powdery mildew affected fruits picked separately from low-
quality fruits was 2.7- and 4.2-fold higher in control plants than in the
UVC-plants, in ’Sonsation’ and ’Malling centenary’, respectively
(Table 1). The differences in treatment effects on the proportion of
marketable, non-marketable, and low-quality fruits were more pro-
nounced in ’Sonsation’ than in ’Malling Centenary’.
Table 1
Effect of UVC radiation on the average (SE) fresh mass of the fruits, total yield (sum of marketable and non-marketable fruits) and the proportions of marketable, low
quality and powdery mildew infected (only in 2022) fruits in strawberry cultivars ’Malling centenary’ (MC), ’Limalexia’ (L) and ’Sonsation’ (S) grown in a strawberry
tunnel during the growing seasons 2021 and 2022 in Central Finland. P values for the main effect of treatment (T) and interaction of treatment and cultivar (TC) are
shown.
Cultivar, year Treatment Average fruit size, g Tot. yield per plant, g Marketable fruits, % Low quality fruits, % Powdery mildew infected fruits, %
MC, 2021 Control 14.3 (0.3) 306.9 (17.8) 68.5 (0.5) 31.5 (6.3) NM
MC, 2021 UVC 13.8 (0.4) 307.0 (18.3) 87.5 (2.7) 12.5 (2.7) NM
L, 2021 Control 12.9 (0.3) 482.6 (11.9) 61.0 (3.6) 39.0 (3.6) NM
L, 2021 UVC 12.5 (0.7) 463.1 (22.7) 82.1 (0.5) 17.9 (0.5) NM
​ ​ ​ ​ ​ ​ ​
P value T 0.288 0.563 0.012 0.012 NM
​ TC 0.854 0.506 0.521 0.521 NM
​ ​ ​ ​ ​ ​ ​
MC, 2022 Control 16.1 (0.6) 488.1 (17.2) 71.2 (3.1) 6.3 (0.5) 22.5 (3.2)
MC, 2022 UVC 16.5 (0.5) 505.5 (24.4) 87.3 (2.8) 4.4 (0.8) 8.3 (2.0)
S, 2022 Control 14.1 (0.4) 617.2 (24.3) 52.9 (3.7) 7.2 (0.8) 39.8 (3.7)
S, 2022 UVC 13.5 (0.4) 563.8 (15.9) 82.6 (3.0) 8.0 (0.6) 9.4 (2.6)
​ ​ ​ ​ ​ ​ ​
P value T 0.813 0.227 <0.001 0.987 <0.001
​ TC 0.324 0.032 0.031 0.008 0.003
MN ˆ not measured.
J. Riikonen et al. Scientia Horticulturae 338 (2024) 113706 
5 
3.2. Brix, acidity, total phenolics, total anthocyanins, and ascorbic acid
concentration
The impact of UVC treatment on fruit quality varied depending on
the year, sampling time, and specific cultivar under consideration.
In 2021, fruits treated with UVC showed elevated brix levels,
although in ’Limalexia’, this effect was observed solely during the first
sampling (treatment  cultivar, P ˆ 0.002) (Fig. 5a). However, in 2022,
brix levels were lower in fruits treated with UVC compared to the control
group (Fig. 5d).
UVC increased acid levels in 2021 across both samplings (Fig. 5b).
Yet, in 2022, acid levels were lower in UVC-treated fruits compared to
the controls, although this difference was only marginally significant in
the first sampling (Fig. 5e).
In 2021, UVC treatment increased anthocyanin concentration in the
first sampling, while no treatment effect was found in the second sam-
pling (Fig. 5c). In 2022, anthocyanins were higher in UVC-treated fruits
in ’Malling centenary’, although the increase was significant only in the
first sampling (treatment  cultivar P ˆ 0.029 and 0.064 in the first and
second sampling, respectively) (Fig. 5f).
In 2021, UVC treatment resulted in an increase in total phenolics
during both samplings, with a more pronounced effect observed in
’Malling centenary’ during the second sampling (Fig. 5g). However, in
2022, total phenolics decreased in the first sampling due to UVC treat-
ment, while their concentration remained unchanged during the second
sampling (Fig. 5h).
Regarding ascorbic acid concentration, fruits exposed to UVC treat-
ment showed higher levels in ’Sonsation’ (treatment  cultivar P ˆ
0.015), whereas no treatment effect was observed in ’Malling centenary’
(Fig. 5i).
3.3. Fruit firmness
Following refrigeration for either two days (’Malling centenary’) or
Fig. 5. Quality properties of fruits (SE) collected from control (gray bars) and UVC-treated (white bars) plants of strawberry cultivars ’Limalexia’ and ’Malling
centenary’ in 2021 (a–c, g) and ’Sonsation’ and ’Malling centenary’ in 2022 (d–f, h, i), sampled twice (S1 and S2) during each growing season within a strawberry
tunnel in Central Finland. Main effects of treatment (T) and statistically significant interactions of T and cultivar (C) derived from mixed model ANOVA are shown.
Table 2
Average values (SE) for fruit firmness, measured in grams using a penetrom-
eter after two days (’Malling Centenary’, MC) or three days (’Sonsation’) in the
refrigerator.
Cultivar Treatment Firmness (g)
MC Control 312.8 (21.6)
MC UVC 390.3 (35.4)
’Sonsation’ Control 333.5 (26.2)
’Sonsation’ UVC 368.2 (13.5)
J. Riikonen et al. Scientia Horticulturae 338 (2024) 113706 
6 
three days (’Sonsation’), fruits subjected to UVC treatment exhibited
increased firmness compared to the control fruits (main effect of treat-
ment P ˆ 0.004) (Table 2).
3.4. UVC and P. aphanis effects on VOC profile
The application of UVC treatment significantly influenced the VOC
profile of ’Malling centenary’ (Fig. 6a, b). Specifically, the fruits exposed
to the UVC treatment exhibited increased emission rates of methyl
salicylate, methyl isovalerate ‡ methyl-2-methylbutyrate, isobutyl
butyrate, ethyl butyrate, and ethyl caproate compared to the control
group (Fig. 6b). Conversely, emissions of methyl caprylate, methyl
crotonate, and germacrene-D were lower in the UVC treated fruits
(Fig. 6b). Notably, the presence of P. aphanis did not yield a significant
effect on the VOC profile.
In ’Sonsation’, PC 1 accounted for 43.8 % of the variance in the data,
showing no significant influence of either the UVC treatment or
P. aphanis infection (data not shown). PC 2 explained 14.4 % of the
Fig. 6. PCA score plots (a,c) and loading plots (b,d) illustrating the volatile compound profiles of strawberry cultivars ’Malling Centenary’ (a,b) and ’Sonsation’ (c,d)
subjected to either UVC exposure (white symbols) or kept under control conditions (black symbols). Shapes denote different sample conditions: squares represent
visibly intact samples, triangles indicate samples with initial signs of P. aphanis infection, while diamonds represent those with severe P. aphanis infection. The
percentages denote the variation in data explained by principal components (PCs), with numbers corresponding to various compounds: 1. Methyl acetate, 2. Ethyl
acetate, 3. Methyl propionate, 4. Isopropyl acetate, 5. Isopropyl acetate‡1-butanol, 6. S-methyl thioacetate, 7. Methyl butyrate, 8. Dimethyl sulfide, 9. Methyl
crotonate, 10. Methyl isovalerate ‡Methyl  2-methylbutyrate (coeluted), 11. Ethyl butyrate, 12. Butyl acetate, 13. Methyl valerate, 14. Isopropyl butyrate, 15. Ethyl
2-methylbutyrate, 16. Ethyl isovalerate, 17. (E) 2-hexenal, 18. (Z) 3-hexenol, 19. 2-Methyl butyric acid, 20. Isoamyl acetate, 21. 2-methylbutyl acetate, 22. Methyl
3-methylvalerate, 23. Two co-eluted compounds, the other potentially methyl thiobutyrate, 24. Propyl butyrate, 25. Ethyl valerate, 26. Amyl acetate, 27. Methyl
caproate, 28. Unknown, 29. Isobutyl butyrate, 30. Methyl 2-hexenoate, 31. Sulcatone, 32. Butyl butyrate, 33. Ethyl caproate, 34. (Z) 3-hexenyl acetate, 35. 1-Hexyl
acetate, 36. (E) 2-hexenyl acetate, 37. Isopropyl caproate, 38. Butyl isovalerate, 39. Isoamyl butyrate, 40. Amyl butyrate, 41. Mesifurane, 42. Linalool, 43. Methyl
caprylate, 44. Benzyl acetate, 45. Butyl caproate, 46. (E) 2-hexenyl butyrate, 47. Methyl salicylate, 48. Octyl butyrate, 49. Linalyl isobutyrate, 50. Geranyl acetone,
51. γ-Decalactone, 52. Germacrene-D, 53. (E, E)-α-farnesene,54. α-Muurolene, 55. Nerolidol. Emission rates of the compounds are shown in Table S2.
J. Riikonen et al. Scientia Horticulturae 338 (2024) 113706 
7 
variation, while PC 3 explained 12.9 % (Fig. 6c, d). The impact of the
UVC treatment on the VOC profile was marginally significant (Fig. 6c),
whereas severe P. aphanis infection (class 2 vs. class 0 and 1) signifi-
cantly affected PC3 (Fig. 6c). Samples exhibiting severe P. aphanis
infection displayed higher emissions of methyl propionate, butyl iso-
valerate, 2-methylbutyl acetate, isopropyl butyrate, isopropyl acetate,
and isoamyl acetate (Fig. 6d). Conversely, samples from the UVC
treatment and those with no or very mild symptoms of P. aphanis
infection showed increased emissions of linalyl isobutyrate, (E) 2-
hexenyl butyrate, and sulcatone (Fig. 6d).
3.5. Leaf properties
Symptoms of powderymildewwere stronger in control plants than in
UVC-treated plants (Table 3, Fig. 7). The treatment exhibited no sig-
nificant influence on the chlorophyll index. However, flavonols and leaf
dry mass content were higher in control plants, whereas NBI and SLA
were lower when compared to UVC-treated plants (Table 4). The feeding
damage in the leaves remained unaffected by the treatment (data not
shown).
4. Discussion
Throughout the experiment, the growth of P. aphanis in all three
tested strawberry cultivars was effectively restrained by the nightly
application of UVC treatment from planting to the final picking. The
application of UVC treatment resulted in a higher overall marketable
crop yield without altering the average size of the fruits. In previous
experiments where plants were irradiated from flowering to the final
harvest, crop yield was either remained unaffected (Janisiewicz et al.,
2016 [0.012 kJ/m2 once a week]; Forges et al., 2020 [once a week 1.7
kJ/m2]) or decreased (de Oliveira et al., 2016 [0.5 kJ/m2 every four
days]). The variability in results could stem from differing experimental
conditions, including the intensity and duration of UVC exposure, as
well as the specific strawberry cultivars used. As the plants were irra-
diated every night, our findings do not provide sufficient evidence to
determine the maximum irradiation interval that would effectively
prevent Powdery mildew.
In our experiment, the cumulative UVC dose was 1.54 kJ/m2 in 2021
(over 11 weeks of exposure) and 1.82 kJ/m2 in 2022 (spanning 13 weeks
of exposure). Notably, the single exposure dose of 0.02 kJ/m2 utilized in
our experiment is considerably smaller than the doses employed in the
majority of previous experiments involving strawberries, conducted
either in controlled conditions (Xu et al., 2017; Sun et al., 2020; Takeda
et al., 2021) or in greenhouses (Van Hemelrijck et al., 2010; Van Delm
et al., 2014; Xie et al., 2016; Forges et al., 2020). The UVC dose
administered in our experiment aligns more closely with the doses of
0.068–0.170 kJ/m2, applied 1–2 times per week in an open field
experiment (Onofre et al., 2021), the dose of 0.012 kJ/m2 applied twice
weekly in tunnel conditions (Janisiewicz et al., 2016), and some of the
doses of 0.030–120 kJ/m2 applied three times a week in a glasshouse
(Verwoort et al., 2020). It’s noteworthy that we did not observe
UVC-induced leaf injuries in our experiments. In contrast, Van Delm
et al. (2014) reported leaf burning, while de Oliveira et al. (2016)
observed reduced photosynthetic efficiency, leaf biomass, and crop yield
in strawberry plants following exposure to a dose of 0.5 kJ/m2 applied
four times per week. Interestingly, Forges et al. (2020) found that a UVC
dose of 1.70 kJ/m2 applied once a week did not reduce photosynthetic
capacity in strawberry leaves. The discrepancies observed among
various experiments underscore the influence of environmental condi-
tions on plant responses to UVC irradiation. The complexity of the in-
teractions makes it difficult to interpret the results.
The rapid growth of strawberry plants during the growing seasons
led to the development of dense canopies. Due to the short wavelength
composition of UVC radiation, it does not penetrate deeply into the
canopy or inside the plant tissues (Stevens et al., 1998). Therefore, the
UV treatment’s direct impact on P. aphanis was only possible on the
surfaces of leaves and fruits not covered by other plant parts. This sug-
gests that UVC treatment may have stimulated induced plant resistance
against powdery mildew. Previous studies have demonstrated that in
response to low-dose UVC irradiation, plants produce reactive oxygen
species (ROS) that can initiate signaling pathways responsible for acti-
vating various defense mechanisms (Urban et al., 2016; Xu et al., 2019;
Forges et al., 2020; Takeda et al., 2021). Xu et al. (2019) found that UVC
significantly induced an overexpression of a set of genes involved in
plant pathogen interaction in leaves of strawberry plants. In our
experiment, the observed elevation in leaf epidermal flavonols and
reduction in specific leaf area and NBI within the control plants might be
linked to the timing of the sampling in early August, coinciding with the
visible presence of fungal biomass on the leaf surface within the control
treatment. Plants are known to synthesize flavonoids in response to
microbial infection (Gorniak et al., 2019).
The phytochemical composition of strawberry fruit has been shown
to be influenced by UVC irradiation, whether applied preharvest (de
Oliveira et al., 2016; Severo et al., 2017; Xu et al., 2017) or postharvest
(Pombo et al., 2011; Li et al., 2014; Severo et al., 2015). In our experi-
ment, the effect of UVC treatment on fruit quality showed in-
consistencies between the two experimental seasons. Interestingly, in
2021, UVC-treated plants showed increased brix levels, acidity, and total
phenols in their fruits. However, these responses to UVC treatment were
reversed in 2022. These variations may be attributed to differences in
growth conditions (Fig. 1) and sampling dates between the experimental
years. Planting was initiated two weeks earlier in 2022 than in 2021,
coinciding with markedly higher air temperatures in 2021. Different
early-season conditions may also contribute to the observed lower crop
yield in 2021 relative to 2022. Also, in previous experiments on straw-
berries, the responses of phytochemical compounds to UVC preharvest
treatment appear to be contingent upon factors such as UVC dose (de
Oliveira et al., 2016; Xu et al., 2017), cultivar (Xie et al., 2015; Forges
et al., 2018), and season (Xie et al., 2016).
In our experiment, the effect of UVC irradiation on anthocyanin
concentration varied depending on the cultivar, with the concentration
either increasing or remaining unchanged due to the UVC treatment.
Anthocyanins, pivotal for the vibrant range of reds, purples, or blues in
strawberries, contribute significantly not only to coloration but also to
antioxidant properties and potential health advantages (Li et al., 2017).
Previous studies have indicated that UVC exposure has the potential to
induce a redder hue in strawberries (Xie et al., 2016; Forges et al., 2020).
The observed increase in ascorbic acid concentration in ’Limalexia’ due
to UVC treatment lends support to the notion of preharvest UVC treat-
ment potentially enhancing the nutritional value of the crop, as sup-
ported by findings in other experiments (Severo et al., 2017; de Oliveira
et al., 2016; Xu et al., 2019).
Preharvest UVC treatment can impact the shelf life of strawberries by
inhibiting microbial growth and stimulating their secondarymetabolism
(de Oliveira et al., 2016; Xu et al., 2017; 2018). In our experiment, the
higher firmness values observed in UVC-treated fruits after 2–3 days of
refrigeration suggests a potential delay in fruit softening. This result is
consistent with earlier research that suggests a delay in the softening of
strawberries as a result of UVC treatment (Xie et al., 2015; 2016).
Table 3
Symptoms of powdery mildew in leaves of strawberry cultivars ’Malling cen-
tenary’ (MC) and ’Sonsation’, scored on 2 August and 8 August 2022 according
to scale modified from Simpson (1987).
Cultivar Treatment Score
2 August
Score
8 August
MC Control 0.4 1.1
MC UVC 0 0
’Sonsation’ Control 1.3 2.1
’Sonsation’ UVC 0 0.1
J. Riikonen et al. Scientia Horticulturae 338 (2024) 113706 
8 
However, it contrasts with some other research outcomes (de Oliveira
et al., 2016; Severo et al., 2017).
The alterations noted in the VOC profile indicate that UVC treatment
has the potential to impact aroma compounds. For instance, compounds
like ethyl butyrate and methyl-2-methylbutyrate, which increased due
to UVC exposure, play a role in creating the fruity strawberry aroma
(Ulrich et al., 1997; Nuzzi et al., 2008). Currently, the direct volatile
emissions from P. aphanis or the metabolic alterations it triggers in
strawberries are yet to be fully understood. However, the altered emis-
sion profile characterized by increased methyl propionate, butyl iso-
valerate, 2-methylbutyl acetate, isopropyl butyrate, isopropyl acetate,
and isoamyl acetate, alongside decreased linalyl isobutyrate, (E)
2-hexenyl butyrate, and sulcatone, may contribute to an unpleasant
taste in fruits affected by powdery mildew disease. Notably, sulcatone’s
aroma has been linked to the pleasant, sweet taste of strawberries (Fan
et al., 2021). Information regarding the impact of preharvest UVC
Fig. 7. Strawberry plants cultivated within a tunnel in Central Finland were photographed on 15 September 2021, and 15 September 2022. In 2021 (a) and 2022 (c),
one portion of the plants was exposed to a nightly UVC dose of 0.02 kJ/m2 from the time of planting until the final harvest, while the other half of the plants acted as
control groups in 2021 (b) and 2022 (d). The presence of powdery mildew symptoms is evident, manifested as leaf curling and a reddish discoloration.
J. Riikonen et al. Scientia Horticulturae 338 (2024) 113706 
9 
irradiation on the sensory attributes of strawberries is limited. Forges
et al. (2020) found that preharvest UVC treatment did not alter the taste
of the fruits compared to the control group.
Methyl salicylate is synthesized from salicylic acid, which is induced
by various biotic and abiotic factors, including UVC exposure. This
compound offers protection against P. aphanis infection (Fragniere et al.,
2011; Feng et al., 2020; Gondor et al., 2022). The presence of methyl
salicylate solely in the ’Malling Centenary’ cultivar, along with
increased emissions under UVC treatment, may have contributed to
UVC’s protective role against powdery mildew disease. This phenome-
non might also explain the reduced susceptibility of ’Malling Centenary’
to P. aphanis infection compared to ’Sonsation’.
In many experiments investigating the effects of UVC irradiation on
preventing microbial growth in growing plants or fruits after harvest, low-
pressure mercury vapor lamps have been utilized. Their irradiance peaks
at 254 nm, which has been recognized as the optimal wavelength for
maximum germicidal action (Singh et al., 2021). Although UVC LEDs are
still expensive and under development, we employed UVC irradiation
using LED technology to develop a custom-made device for research
purposes. The LED type available during the construction of our device
has its peak irradiance at 276 nm and emits radiation within the UVB
range as well. While UVB is recognized for its ability to stimulate sec-
ondary metabolism, bolster plant defenses, and disinfect microbes, its
efficacy typically requires prolonged exposure spanning several hours or
days (Urban et al., 2018). Furthermore, in our preliminary test, we
examined the impacts of varying UV-wavelength ranges and exposure
durations on grey mold (Botrytis cinerea) and Scleroderris canker (Grem-
meniella abietina) through agar plate experiments. Contrary to UVC irra-
diation, our findings indicate that UVB irradiation had no discernible
effect on the dry mass or conidial germination of either species (unpub-
lished results). While acknowledging the potential impact of UVB radia-
tion on the parameters examined in this experiment, our findings suggest
that the plant responses to the irradiation treatment were predominantly
influenced by UVC range exposure. Advancements in the development of
UVC LEDs, specifically those peaking closer to 254 nm, could potentially
facilitate shorter durations for each UVC treatment.
5. Conclusions
Our findings indicate that the UVC irradiation method is not only
effective in preventing powdery mildew but also has the potential to
enhance the nutritional value and prolong the shelf life of fruits. The
treatment can modify the sensory attributes of the fruit, either directly
or indirectly, by altering its VOC profile through disease management.
These outcomes collectively demonstrate the diverse benefits of UVC
treatment, illustrating its ability to improve disease resistance and
enhance specific fruit characteristics.
We conclude that powdery mildew prevention can be effectively
achieved through pre-harvest, short-duration UV irradiation peaking at
the border between UVC and UVB spectra. The expected decrease in
prices of UVC LEDs over time is likely to lead to their increased inte-
gration into practical plant disinfection solutions, owing to their
adaptability and energy efficiency.
Declaration of competing interest
Authors declare that they have no conflict of interest.
Funding source
This work was supported by the Centre for Economic Development,
Transport and the Environment, North Savo [Grant No. 157288]; and
the Natural Resources Institute Finland.
CRediT authorship contribution statement
Johanna Riikonen: Writing – original draft, Visualization, Project
administration, Methodology, Investigation, Funding acquisition,
Formal analysis, Data curation, Conceptualization. Hanna Ruhanen:
Writing – review & editing, Methodology, Investigation, Conceptuali-
zation. Anne Uimari: Writing – review & editing, Methodology,
Investigation, Conceptualization. Marja Poteri: Writing – review &
editing, Methodology, Investigation, Conceptualization.Anna Toljamo:
Writing – review & editing, Investigation. Harri Kokko: Writing – re-
view & editing, Investigation. James D. Blande: Writing – review &
editing, Investigation. Raija Kumpula: Writing – review & editing,
Investigation. Minna Kivimaenpaa: Writing – original draft, Visuali-
zation, Methodology, Investigation, Formal analysis.
Declaration of competing interest
The authors declare the following financial interests/personal re-
lationships which may be considered as potential competing interests:
Johanna Riikonen reports financial support was provided by The
Centre for Economic Development, Transport and the Environment,
North Savo. If there are other authors, they 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 will be made available on request.
Acknowledgments
We are grateful to Jukka Laitinen and Aleksi Sirkka for maintenance
of the experiment, and for Jarkko Hanninen, Liisa Kauppinen, Milla
Kossi, Sirpa Makinen, Sari Vattu and Oliver Welling for the data
collection. Dianne Jans and Kinga Landzinska are thanked for their
contribution to the analysis of strawberry quality.
Supplementary materials
Supplementary material associated with this article can be found, in
the online version, at doi:10.1016/j.scienta.2024.113706.
Table 4
Impact of UVC radiation on leaf chlorophyll and flavonoid indexes, and Nitrogen Balance Index (NBI) obtained by Dualex®, leaf dry mass content and specific leaf area
(SLA) (SE) of strawberry cultivars ’Malling centenary’ (MC) and ’Sonsation’ cultivated within a strawberry tunnel in Central Finland and sampled on 2 August 2022.
P values for the main effects of treatment obtained from mixed model ANOVA are shown.
Cultivar Treatment Chlorophyll Flavonols NBI Leaf
dry mass content, %
SLA, cm2/ g
MC Control 31.6 (0.4) 1.44 (0.02) 22.3 (0.3) 33.2 (0.3) 7.3 (0.19)
MC UVC 32.0 (0.8) 1.35 (0.02) 24.1 (0.4) 31.4 (0.4) 8.3 (0.13)
’Sonsation’ Control 30.1 (2.0) 1.57 (0.03) 19.5 (0.8) 33.8 (0.8) 7.6 (0.23)
’Sonsation’ UVC 30.9 (0.8) 1.44 (0.03) 21.9 (1.0) 31.6 (0.1) 8.5 (0.23)
P value Treatment 0.942 <0.001 0.005 0.020 <0.001
ns, not significant.
J. Riikonen et al. Scientia Horticulturae 338 (2024) 113706 
10 
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