RESPONSES OF CUCUMBER CULTIVARS TO INDUCTION OF SYSTEMIC RESISTANCE AGAINST ANTHRACNOSE BY PLANT-GROWTH PROMOTING FUNGI

Initial experiment on the reactions of five Japanese cultivars of cucu mber to Colletotrichum orbiculare infection in the greenhouse revealed that cv Suyo and Gibai were susceptible and moderately susceptible, r espectively, while cv Shogoin fushinari and Sagami hanjiro were resist ant to infection by C. orbiculare; cv Ochiai fushinari was moderately resistant. The ability of 16 plant growth promoting fungi (some isolat es belonged to species of Phoma and some non-sporulating isolates) iso lated from zoysiagrass rhizospheres to induce systemic resistance in t he above five cucumber cultivars was tested by growing plants in potti ng medium infested with barley grain inocula of PGPF in the greenhouse . The second true leaves of 21-day-old plants were challenge inoculate d with C. orbiculare and disease assessed. Nine, out of 16 isolates, c aused significant reduction of disease caused by C. orbiculare in at l east two cultivars. Phoma isolates (GS8-1 and GS8-2) and non-sporulati ng isolates (GU21-2, GU23-3, and GU24-3) significantly reduced the dis ease in all the five cultivars. The disease suppression in cucumber wa s due to the induction of systemic resistance, since the inducer(s) an d the pathogen were separated spatially and that the inducer did not c olonize aerial portions. The resistance induced by certain isolates in a susceptible cultivar was less than that in a resistant cultivar. Di sease suppression caused by isolate GU21-2 was similar to the C. orbic ulare induced control in certain cultivars. The average rate of expans ion of lesion diameter on leaves due to C. orbiculare was slower due t o induction with the selected plant growth promoting fungi compared to the uninduced control plants. Roots of four cultivars were colonized by only three isolates, however, roots of one cultivar (Suyo) was colo nized by five isolates suggesting the cultivar-specific root colonizat ion ability.