Survival of Chlamydospores of Phytophthora cinnamomi in Several Non-Sterile, Host-Free Forest Soils and Gravels at Different Soil Water Potentials

Abstract

Chlamydospore survival was investigated for six soil types, collected from disease-free areas of native forest in Victoria, in 50-g packs of non-sterile, unamended soils and gravels at five different matric soil water potentials ( ψ ). No chlamydospores survived in gravel free from OM, and only one chlamydospore survived at ψ -3000 kPa. In other packs the numbers of chlamydospores declined for 2 months then increased markedly at 4-6 months. Many chlamydospores remained viable for 8 months and some for 10 months despite the use of non-sterile soil and the absence of hosts. Maximum numbers survived in gravel from the Brisbane Ranges 6 and 8 months after inoculation at ψ -500 kPa. Decreasing soil moisture appeared to stimulate chlamydospore formation while a low rganic matter content and small numbers of microorganisms increased survival.