ABSTRACT
The utility of fatty acid profiles for characterization and differentiation of isolates of P. infestans was investigated. Two libraries of fatty acid methyl ester (FAME) profiles (one representing average genotype characteristics and one representing individual isolate characteristics) were established from at least eight replicate samples of each of 25 different isolates of P. infestans, including representative isolates of US-1, US-6, US-7, US-8, US-11, US-14, and US-17 genotypes. These libraries then were used to identify and characterize additional unknown isolates. Fatty acid profile characteristics also were compared with cultural and genetic characteristics of the isolates. FAME profiles for isolates of P. infestans were consistent over multiple extractions and distinctly different from profiles for isolates of other Phytophthora species, such as P. capsici and P. erythroseptica, as well as isolates of Pythium spp. and various other fungal groups. Overall, profiles from different isolates within the same genotype shared similar characteristics, although there was overlap among some genotypes. Incubation temperature, growth medium, and prolonged storage on agar media all significantly affected fatty acid profiles; however, when these conditions were kept constant, profiles were distinct, consistent, and reproducible over time. Isolate profiles were sufficiently specific that individual isolates could be distinctly identified by FAME profiles. In general, individual isolate characteristics were more determinant than genotype group characteristics, although genotype could be determined for most isolates tested. Results indicated that FAME profiles can be an additional tool useful for characterizing isolates and populations of P. infestans.
