INDUCTION OF SYSTEMIC RESISTANCE IN CUCUMBER AGAINST CUCUMBER BEETLES(COLEOPTERA, CHRYSOMELIDAE) BY PLANT GROWTH-PROMOTING RHIZOBACTERIA

Field studies were conducted in 1993 and 1994 to evaluate the effects of induced resistance in cucumber by plant growth-promoting rhizobacte ria (PGPR) on numbers of the spotted cucumber beetle, Diabrotica undec impunctata howardi Barber, and the striped cucumber beetle, Acalymma v ittatum (F.). Cucumber plant growth and yields were significantly (P<0 .05) greater, and populations of cucumber beetles were significantly l ower, on PGPR-treated cucumber than on nontreated cucumber. On dates w hen peak beetle populations were present, PGPR treatment resulted in s ignificantly (P<0.05) greater cucumber beetle control than weekly appl ications of esfenvalerate insecticide. In no-choice greenhouse cage ex periments with 3 cucumber cultivars, beetles infected with the cucurbi t Milt pathogen, Erwinia tracheiplila, were released and allowed to fe ed on PGPR-treated or nontreated cucumber Plants. The incidence of cuc urbit wilt disease was significantly (P<0.05) lower on PGPR-treated cu cumber plants than on nontreated plants. These results indicate that P GPR-induced resistance may be more effective than insecticides for con trol of cucumber beetles and cucurbit wilt disease on cucumber. Possib le mechanisms for PGPR-induced resistance against cucumber beetles are discussed.