Epidemiological aspects of the oat kernel spot, caused by Pyrenophora chaetomioides

Abstract

The expansion in acreage of oats in Brazil, particularly under no till system, has increased the frequency of foliar and kernel spots caused by Pyrenophora chaetomioides. As a necrotrophic, this fungus is extremely dependent on crop debris to survive from one crop season to another. Consequently, the susceptibility of the host, the presence of inoculum and favorable environmental conditions have been the chief aspects for the frequent occurrence of epidemics in South Brazil. The objective of this work was to identify the stages of development of the seed that are most susceptible for the establishment of the fungus and to correlate it with the amount of inoculum produced on lower dead leaves as well as with the environmental conditions. Under field conditions oat panicles were exposed to the inoculum for certain periods of time since their extrusion and to different conditions of temperature and water precipitation. Seeds exposed to inoculum at both milk and early dough stages showed the highest frequency of infection of P. chaetomioides. The temperature and water precipitation did not influence the percentage of seeds infected. However, environmental conditions such as high temperatures, excess of rain and the presence of other diseases anticipated the senescence of oat basal leaves, favoring a higher production of spores by the pathogen. The use of cultivars that offer resistance or escape to the seed infection, crop rotation and fungicide spray at the right time are some recommended measures to minimize the damage caused by this pathogen.