File(s) under permanent embargo
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.
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.
