DISPERSAL OF PHYTOPHTHORA-CINNAMOMI THROUGH LATERITIC SOIL BY LATERALLY FLOWING SUBSURFACE WATER

Phytophthora cinnamomi was recovered from water flowing at the base of a lateritic soil about 1 m deep and overlying concreted duricrust on a hillslope supporting a severely diseased forest of Eucalyptus marginata (jarrah) in south-western Australia. The water was collected by 20-m-long throughflow interception trenches dug down to the duricrust. The fungus also was recovered at depths greater than 2 m from piezometers drawing water perched on clay beneath the duricrust. Most inoculum-bearing water was collected in winter and early spring when deeper soil was warmer than near-surface soil. Collections also were made in autumn and summer following unseasonably heavy rainfall. Subsurface water flowed through the soil at least 120 m down the hillslope following a moderately intense winter rain event. Propagule density averaged 60 propagules per liter on selected days in spring. At least half of the propagules were identified as zoospores.