Vegetation Damage Caused by Phytophthora cinnamomi on Disturbed Sites in Temperate Rain-Forest in Western Tasmania

Abstract

Phytophthora cinnamomi has been isolated directly from 558 diseased plants among 39 species including 1 fern, 4 graminoids and 34 woody dicotyledons, all indigenous to the cool temperate rainforest of Tasmania. Pathogenicity has been proved by greenhouse tests (20 spp.) and by field inoculation at two localities (19 spp.). Of the 142 species in the rainforest flora, 69 were rated for the susceptibility of field populations; 30% were highly susceptible and less than 5% highly resistant. High proportions of susceptible species occurred in Epacridaceae, Eucryphiaceae and Proteaceae.

All 93 isolates tested were the common A₂ mating type. The fungus was constantly associated with disease at 47 survey localities. Diseased plants were widely but patchily distributed along exposed road and track edges within unburned rainforest and in recently burned rainforest. The fungus was not recovered from samples taken beneath healthy roadside regeneration, beneath undisturbed rainforest or above 900 m elevation.

The disease has the characteristics of attack by a recent invader and appears to be dependent upon disturbance which elevates soil temperatures above 15°C, the lower threshold for infection by P. cinnamomi. Post-fire recovery of forest canopy is expected to allow re-establishment from external sources of seed of those susceptible species which are both efficiently dispersed and tolerant of shade. Species lacking such characteristics are at risk of local elimination but no single rainforest species appears to be under threat of extinction from this pathogen.