Epsilon Archive for Student Projects

Abstract

Phytophthora infestans is the most serious pathogen on potato worldwide. The pathogen has several problematic characteristics such as a mixed reproduction system, polycyclism and a high genetic plasticity rendering it prone to adapt to new situations, e. g. by developing resistance to fungicides. Resistance has previously been reported for fungicides such as metalaxyl, propamocarb, mandipropamid (MPD) and oxathiapiprolin (OTP). This study surveys P. infestans isolates collected in Swedish fields during the season 2023 for resistance to MPD and OTP, resistances which have not been found in Sweden before. A floating leaf disc assay with concentration series for both fungicides was deployed for phenotyping the isolates. To connect any resistance to SNPs found to cause resistance in previous research, target genes PiCesA3 for MPD and ORP1 for OTP were Sanger sequenced. In addition, some isolates were sent to the James Hutton institute in Scotland for microsatellite genotyping in order to investigate if resistance can be connected to a specific SSR genotype of P. infestans.
One P. infestans isolate collected in a conventional field plot were able to infect and sporulate on leaf discs in all fungicide concentrations of the floating leaf disc assay while all other isolates were completely inhibited at higher concentrations. Unfortunately, Sanger sequencing failed and for this particular isolate and it was not among the isolates sent for microsatellite genotyping. Hence, resistance could not be connected to any specific SNP or SSR genotype. The 10 isolates displaying normal sensitivity could not be attributed any specific SSR genotype but were classified as ‘other’, as is the normal situation for Swedish P. infestans isolates. The resistance found in this study is of interest for future fungicide use. However, since it was only found in a single isolate, more comprehensive studies are needed to assess the situation and produce a more representative picture of the in-field situation in Sweden.