Comparative Pathogenicity of Fourteen Australian Isolates of Phytophthora cinnamomi Determined on Transplants of Tasmanian Temperate Heathland

Abstract

Peat cores containing mature plants of 21 native species were transplanted from heathland in south- western Tasmania to a greenhouse and inoculated individually with 14 Australian isolates of Phytophthora cinnamomi. The isolates, which had been obtained from 10 different species of host plants and from 14 localities widely distributed across the continent, included three of the four isotypes of the fungus known to occur in Australia. Abnormal coloration, root-rot and death occurred in 9 of the 11 species of dicotyledons present; in a single plant of one species of the 11 monocotyledons but in neither of the two ferns. Of the nine species of dicotyledons in which disease occurred, five species were highly susceptible. Comparisons of the relative pathogenicity of isolates, based on the response of the five highly susceptible species, showed no evidence of strong differences in pathogenicity between groups of isolates, whether these groups were based on isotype of the fungus, climate at the source of the isolates or taxonomic affinity of the host plants from which they were originally isolated.