Variation in pathogenicity among isolates of Phytophthora clandestina

Studies on 25 isolates of Phytophthora clandestina collected from four stat es in southern Australia identified the presence of diversity in pathogenic ity but not in morphology among isolates. Race 0 was found in all states ex cept New South Wales, race I was found in all states, and races 2 and 3 wer e found only in Victoria and New South Wales, respectively. Race 4 was iden tified in Victoria and Western Australia. There was no apparent change in p athogenicity of the fungus following 10 (every 20 days) or 20 (every 10 day s) cycles of subculturing. There was also no shift towards higher aggressiv eness or virulence during 10 cycles of the fungus through susceptible or re sistant cultivars.