Heterothallic Phytophthora: Evidence for Hormonal Regulation of Sexual Reproduction

Abstract

Both A1 and A2 mating types of Phytophthora cinnamomi, Phytophthora parasitica and Phytophthora palmivora formed oospores by selfing when they were paired with different mating types on opposite sides of polycarbonate membranes. The selfing of one mating type in the presence of the other mating type demonstrates the production of diffusible substances like plant hormones as found in related fungi. Young cultures and A2 isolates were better hormone producers, whereas old cultures and A1 isolates were more responsive to hormones in both intra- and interspecific pairings. The polycarbonate membrane method should facilitate identification and genetic studies of heterothallic species of Phytophthora.