The survival of Phytophthora cinnamomi rands in the northern jarrah (Eucalyptus marginata donn ex sm.) forest of Western Australia

The introduced soil-borne plant pathogen Phytophthora cinnamomi Rands causes the death ofjarrah (Eucalyptus marginata Donn ex Sm.) and associated understorey species throughout the jarrah forest of south-west Western Australia. In comparison to other infested forests in Australia, it has been difficult to isolate this pathogen from upland sites. Two aspects of survival of￡. cinnamomi on upland sites in the northern j arrah forest were examined, firstly, the survival of chlamydospores in surface soils, and secondly, the survival of E. cinnamomi in a common susceptible understorey species, Banksia grandis Willd. Chlamydospores of B. cinnamomi were recovered from a lowland water gaining site, but not from an adjacent upland freely draining site at Deer Road, although there was dying vegetation on both sites. Soil moisture contents were significantly higher on the lowland site than on the upland site (P<0.001), and remained high over summer in the former but not in the latter. Axenically produced chlamydospores did not survive in field plots when soil moisture contents decreased below 6.25% or -101 kPa on an uninfested upland site at North-east Road (P<0.001). When soil moisture contents were higher, that is, during winter and early spring, chlamydospores could be recovered for up to 24 weeks. A similar pattern of survival was observed when axenically produced chlamydospores were placed into soil from the North-east Road site and maintained at four different matric potentials in the laboratory. Germination of chlamydospores and the number of chlamydospores with intact cytoplasm were significantly affected by soil moisture (P