Mating Behaviour of Australian Isolates of Phytophthora Species. II. Phytophthora cinnamomi

Abstract

Determinations were made of the patterns of oogonial occurrence in the culture medium, the numbers of oogonia produced and of aborted oogonia formed in matings between 18 A1 and 116 A2 compatability type isolates of Phytophthora cinnamomi from south-eastern and Western Australia.

The majority of the A2 isolates mated freely with their A1 counterparts, but three A2 isolates mated with only some of the A1 testers and five others were sterile. Patterns of occurrence of oogonia, their quantitative production and the percentage of aborted oogonia produced were affected by the particular isolates used. Statistical analysis of the data showed that the nine populations of A2 isolates were significantly different from each other in all three parameters studied. Populations from Eden and Bemm River were markedly less fertile than those from other regions. These findings are consistent with the hypothesis that P. cinnamomi is an allochthonous organism in Australia.

Oogonial size was found to vary according to position within the mating plate and according to the particular isolates used, although different geographical groups of isolates could not be dis- tinguished. Abnormally small oogonia were produced in matings involving three of the A2 isolates. The taxonomic significance of these findings is discussed.