Fungicide tolerance in Phytophthora infestans

Abstract: For the last 180 years, the pathogen P infestans, responsible for the late blight disease, has been a severe problem for farmers. Despite the large efforts and financial investments done in the management of the disease, 15-30% of the potato production is lost to this disease globally each year. The late blight requires a high level of control, where fungicides play a crucial part, to protect the quantity and the quality of the harvest. The use of fungicides is associated with unfavourable consequences, where the risk of a reduced sensitivity to fungicides in the pathogen is one of the more severe. In this study, the aim was to examine how the use of different dosages of the fungicide Infinito affects the genotypic and phenotypic makeup of a P. infestans field population. The population was genetically characterized by using a 12-plex Simple Sequence Repeats (SSRs) method. Sensitivity to the fungicide in vitro was estimated based on radial growth on Infinito-amended rye-pea agar. The result of the study revealed a population with an unexpectedly narrow genotypic diversity. In the in vitro fungicide tests, no distinction between isolates from treated and untreated plots were observed. Neither were there any signs of selection towards more tolerant genotypes and no significant differences between individual isolates was observed.