Induction of Sexual Reproduction in Single A2 Isolates of Phytophthora Species by Trichoderma viride

ABOUT half the species of Phytophthora, including many important plant pathogens such as P. palmivora, P. cinnamomi and P. infestans, are heterothallic. Consistent induction of sexual reproduction in agar cultures of heterothallic species requires the pairing of isolates of the two compatibility groups, A¹ and A² (refs. 1–3). Although sex organs are occasionally formed in cultures of single isolates, such isolates though intrinsically bisexual are normally self-sterile^2–3. In consequence it has been assumed that in nature the presence of both compatibility types is required for the formation of oospores.