Self-fertility in two clonal lineages of Phytophthora infestans

Abstract

Oospores were identified in pure culture of Phytophthora infestans strains 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 for P. infestans and other Phytophthora species 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 for Glucose-6-phosphate isomerase allozyme patterns revealed that six had genotypes different from the parental isolate.