Changes in root tissue associated with infection by Phytophthora cinnamomi

Phytophthora cinnamomi Rands causes root rot in a wide range of Victorian native species. In native forests resistance to the pathogen is rare and difficult to detect because many tolerant species {sensu DAY 1974), whose root tissues are invaded and colonized, co-exist with the pathogen without producing symptoms. However, under certain conditions, such as on shallow soils or when exposed to successive periods of drought and water saturation, species which are usually tolerant may develop symptoms and die. The selection of inherently resistant species is therefore difficult and tedious. Studies of relationships between P- cinnamomi and both resistant and susceptible host species have demonstrated that in all species examined to date the roots both attract and are penetrated by zoospores (HINCH and WESTE 1979). In pilot studies on dianges in root tissue inoculated with P. cinnamomi massive changes in conductivity of a bathing fluid were detected in susceptible species but were significantly less for resistant species. Changes m tissue permeability are an important early indication of pathogenesis (THATCHER 1939, 1942, WHEELER 1976, Dow and CALLOW 1979), and can be measured. The present paper reports the results of tests to determine whether a sequential study of such conductivity changes in fluid bathing inoculated seedling roots would be useful in screening for resistance to P cinnamomi.