Fungicide Sensitivity and Oxysterol Binding Protein Inhibitor Mutations Associated with Oxathiapiprolin Resistance in Indonesian Populations of Phytophthora infestans

A total of 24 samples, consisting of 12 each of leaf and pure culture DNA isolates were collected for the in vitro investigation of the resistance of Phytophthora infestans to fungicides. Based on the genotype simple sequence repeats matcher, most were identified as the A1 mating type, #8 as the A2 type, and #6 was unidentified with main genotypes were ID genotype; EU_2_A1; and EU_33_A2. The poisoned food assay showed that several isolates, such as #6, #32, and #35 were highly resistant to certain actives including oxathiapiprolin + famoxadone, but were sensitive to oxathiapiprolin + chlorotalonil, except #39, which was resistant to both. Metalaxyl application resulted in four resistance, three medium resistance, one reduced sensitivity, and five sensitive phenotypes. Oxysterol binding protein inhibitor revealed diverse mutations in each sample, where the highest number of mutations was in #93 and #6, whereas the lowest was in #32, #58, and #83. The most common mutation site was K884C/E/R. S768D/N and especially G770A/V were found in #39 and #78. Poison bait and mutation analysis described the resistance level variations in each sample and population. Population structure examined that Wonosobo population was close to or a part of Banjarnegara due to a similar genotype composition. Both populations were also close to Magelang but not as close to each other. Inter-population genotype migration including the resistance one was assumed from Wonosobo to Banjarnegara and Magelang based on a combination of poison bait, mutation, and population genetic structure analyses.