Diagnosis and population analysis of Pythium species using AFLP fingerprinting.
Amplified fragment length polymorphism (AFLP) fingerprinting was used to characterize plant-pathogenic Pythium species and intraspecific populations. Species-diagnostic AFLP fingerprints for Pythium aphanidermatum, P. irregulare and P. ultimum, and tentative fingerprints for 6 other species (P. dissotocum, P. heterothallicum, P. myriotylum, P. torulosum, P. spinosum and P. vexans) were identified. Intraspecific distance analyses of P. aphanidermatum, P. ultimum and P. irregulare revealed distinct patterns of intraspecific variation among the 3 species. P. aphanidermatum showed the smallest mean distance among isolates (15%), followed by P. ultimum (37%). P. irregulare had the largest mean distance among isolates (64%), which were divided into 2 populations with great genetic differentiation (FST=0.2), suggesting the presence of a cryptic species boundary within this species.