Phenotypic variation in a clonal lineage of two Phytophthora cinnamomi populations from Western Australia

Seventy-three isolates of Phytophthora cinnamomi were collected from diseas ed Eucalyptus marginata (jarrah) and Corymbia calophylla (marri) trees in t wo forest communities in the southwest of Western Australia. Both populatio ns of P. cinnamomi were examined for phenotypic and genotypic variation. Mi crosatellite DNA analysis showed that all isolates were of the same clonal lineage. We show, for the first time for P. cinnamomi, that morphological a nd pathogenic variation between populations of the clonal lineage are very broad and continuous, The phenotypes examined included growth rates and col ony morphology on potato dextrose agar at different temperatures, sporangia l and gametangial morphology, ability to form lesions in detached jarrah an d marri stems, and ability to cause deaths of clonal jarrah plants in a gla sshouse trial. Phenotype variation was derived asexually. All phenotypes in vestigated varied independently from one another. Cluster analysis of 24 mo rphological and pathogenicity phenotypes identified two main clusters of is olates corresponding to each population. The ability to cause deaths in bot h populations ranged from killing all plants within 59 d to plants being sy mptomless 182 d after inoculation.