RAPID INDUCTION OF SYSTEMIC RESISTANCE IN CUCUMBER BY PSEUDOMONAS-SYRINGAE-PV-SYRINGAE

Inoculation of the first leaf of cucumber with Pseudomonas syringae pv. syringae (wheat isolate) elicited a rapid hypersensitive response and also induced systemic resistance to Colletotrichum lagenarium. Systemic increases in peroxidase activity and resistance were observed within 1 day of inoculation with P. syringae pv. syringae. The induction of systemic resistance and peroxidase activity by P. syringae pv. syringae was at least 4 days faster than that observed for the cucumber pathogen Pseudomonas syringae pv. lachrymans. Detaching the leaf inoculated with P. syringae pv. syringae at intervals after inoculation demonstrated that the signal(s) involved in systemic induced resistance and increases in peroxidase was generated within 6 h after the inducing inoculation and before the development of visible necrosis. Tn5 mutants of P. syringae pv. syringae, selected for their inability to induce the hypersensitive response and systemic peroxidase activity in cucumber, had also lost their ability to elicit systemic disease resistance in cucumber and cause disease on wheat. A genomic clone was isolated from a library of P. syringae pv. syringae which restored the ability of both mutants to induce the hypersensitive response, systemic disease resistance and peroxidase activity. The rapidity and level of resistance induced by P. syringae pv. syringae suggest that this organism may be useful in future studies on the nature of systemic signaling and the regulation of induced resistance in cucurbits. © 1991 Academic Press Limited.