Mating Behaviour of Australian Isolates of Phytophthora Species. I. Inter- and Intraspecific Mating

Abstract

This paper presents the first detailed report on the mating behaviour of isolates of Phytophthora drechsleri, P. cinnamomi, P. parasitica, P. palmivora, P. cryptogea and P. cambivora from Australia, Papua New Guinea and New Britain. In all, 97 isolates of Australasian origin and four isolates of American origin were examined.

Matings between species produced fewer oogonia and more aborted oogonia than occurred in intraspecific matings. Isolates differed in their abilities to form oogonia in interspecific matings.

Unlike the other species examined, P. drechsleri isolates were unable to form oogonia and oospores in many of the intraspecific matings attempted. In general, the mating patterns of P. Cryptogea isolates were similar to those of P. drechsleri, which supports the conclusion that these taxa are conspecific.

Isolates of P. parasitica mated freely in intraspecific pairings but showed some restrictions in interspecific matings, with aborted oogonia frequently being produced. The behaviour of single- zoospore derivatives from seven P.parasitica isolates that exhibited irregular sexual behaviour during culture showed that three of the field isolates were heterocaryotic, carrying both homothallic and A1 type nuclei.

Both homogenic and heterogenic incompatibility mechanisms may be operative as barriers to free sexual reproduction. The present study indicates that determinations of mating competence are of little taxonomic value.