Phenotypic and Genotypic Characterization of the Population of Phytophthora infestans in Brazil

Recently, phenotypic variations and differences in virulence have been observed among Brazilian isolates of P. infestans. Analysis of phenotypic variability can be useful to understand the pathogen population and how variants may affect late blight epidemics. Thus, this study aimed to characterize the population of P. infestans in Brazil using mating type, mitochondrial DNA haplotype, microsatellite genotype, and mefenoxam sensitivity. Isolates of the A2 mating type from tomato are reported for the first time. Isolates from potato plants were either of A1 or A2 mating types. The Ia and Ib mitochondrial DNA haplotypes were detected in Brazil. The Ia is associated with isolates from potato and the Ib with isolates obtained from potato and tomato. All tomato isolates were of a new genotype, SA_1_A2, while the EU_37_A2 and EU_2_A1 genotypes were detected among isolates sampled from potato fields. The sensitivity to mefenoxam varied: sensitive, intermediately insensitive, and insensitive isolates are present in potato and tomato crops. The population of P. infestans in Brazil remains structured according to host, but genotypes associated with potato or tomato plants seem to vary periodically.