Phytophthora cinnamomi

Phytophthora cinnamomi Rands was first isolated from cinnamon trees in Sumatra in 1922. The pathogen is believed to have originated near Papua New Guinea but now has a worldwide distribution. P. cinnamomi is heterothallic with A1 and A2 mating types; however, even in areas in which both mating types are present, it appears that genetic diversity arises asexually rather than as a result of sexual recombination. P. cinnamomi can grow saprophytically in the soil for long periods, rapidly capitalizing on the advent of favourable conditions to sporulate and produce vast numbers of asexual, biflagellate zoospores. The motile zoospores are attracted to suitable infection sites, where they attach and invade the plant. Within a few days, hyphae ramify throughout the tissues of susceptible plants, forming sporangia on the plant surface and rapidly amplifying the disease inoculum. Over the last 10-15 years, molecular analyses have clarified details of the phylogeny of P. cinnamomi and other Oomycetes. Research on P. cinnamomi has given rise to a more comprehensive understanding of the structure and function of the motile zoospores. New methods have been developed for P. cinnamomi identification and diagnosis. Long-term studies of diseased sites, particular those in southern Australia, have produced a better understanding of the epidemiology of P. cinnamomi diseases. Research has also increased our knowledge of the mode of action and efficacy of inhibitors of P. cinnamomi diseases, especially the phosphonates. This review will present an overview of the advances these studies have made in our understanding of P. cinnamomi pathogenicity, epidemiology and control.