Self-Fertility in Two Clonal Lineages ofPhytophthora infestans

Abstract

Oospores were identified in pure culture ofPhytophthora infestansstrains of the clonal lineages US-7 and US-8 (A2 mating type), but not in the US-1 clonal lineage (A1 mating type). This self-fertility was not due to contamination, a mixture of isolates, or heterokaryosis because all of the single-zoospore isolates (n = 128) from these cultures displayed the same phenotype as the parental isolate from which they were derived. The self-fertility in US-7 and US-8 was different from self-fertility previously reported forP. infestansand otherPhytophthoraspecies because the oospores appeared in young cultures and the mycelia were not appressed to the medium. The number of oospores produced by US-7 and US-8 cultures was much lower than the number produced in response to an A1 mating type isolate. Analysis of eight oospore progeny forGlucose-6-phosphate isomeraseallozyme patterns revealed that six had genotypes different from the parental isolate.