Effect of phosphite in avocado roots on the zoospores of Phytophthora cinnamomi

Levels of phosphite inhibitory to Phytophthora cinnamomi were reached in roots of sixmonth-old Persea americana cv Edranol within seven days after injection with phosphorous acid. Scanning electron microscope (SEM) studies showed no significant differences in the cyst's ability to germinate and infect phosphorous acid treated or control roots. SEM showed severe deterioration of root surfaces in untreated control roots compared to phosphorous acid treated roots. The detached root technique described by Botha et al (1989) proved to be an excellent in vitro method of testing the effectiveness of antifungal activity of systemic fungicides when a highly susceptible plant is used.