A Forest Soil Suppressive to Phytophthora cinnamomi and Conducive to Phytophthora cryptogea. I. Survival, Germination and Infectivity of Mycelium and Chlamydospores.

Abstract

The physical and chemical characteristics of a forest soil suppressive to P. cinnamomi are compared with those of other, previously described, suppressive soils. Recovery of P. cinnamomi chlamydospores from the suppressive soil was reduced to 51% of recovery from condilcive soil when the chlamydospores were mixed through the soil immediately prior to sampling. The subsequent recovery rate decreased more rapidly in the suppressive soil than in the conducive soil. Germination of chlamydospores by the formation of a terminal sporangium and zoospores was inhibited in the suppressive soil. Degeneration of mycelium was more rapid in the suppressive than in the conducive soil.

Glasshouse tests showed infection of seedlings growing in the suppressive soil could occur when a zoospore inoculum was used. Infection was greatly reduced when a chlamydospore inoculum was used.

Field trials in Tallaganda State Forest, N.S.W., indicated that P. cinnamomi introduced into this habitat rarely caused infection and was unlikely to spread.