Phytophthora cinnamomi A1: An ancient resident of New Guinea and Australia of Gondwanan origin?

This article re-examines the hypothesis, first proposed by Shepherd (Search, 6(11-12), 1975, 484), that Phytophthora cinnamomi is an ancient organism in Australia and New Guinea. It further evaluates data that suggest the A1 mating type is Gondwanan in origin and may have been present in New Guinea for up to 10 million years. It is postulated that there has been a mating type change in P. cinnamomi from A1 to A2 in relatively recent times as a result of genetic transformation of the A1 mating type.