INSECT FEEDING ON CUCUMBER MEDIATED BY RHIZOBACTERIA-INDUCED PLANT-RESISTANCE

Select strains of plant growth-promoting rhizobacteria (PGPR) were eva luated in greenhouse experiments with cucumber for induction of resist ance against cucumber beetle (Diabrotica undecimpunctata howardi Barbe r) feeding and the beetle-transmitted cucurbit wilt disease. When beet les were given a choice between PGPR-treated and nontreated cucumber, their feeding on stems and cotyledons and the severity of wilt symptom s were significantly lower on PGPR-treated plants. HPLC analysis demon strated that cotyledons from PGPR-treated plants contained significant ly lower concentrations of the cucumber beetle feeding stimulant cucur bitacin than nontreated plants. These results suggest that a mechanism for PGPR-induced resistance against cucumber beetle feeding may invol ve a change in the metabolic pathway for cucurbitacin synthesis.