INDUCED RESISTANCE OF CUCUMBER TO ANTHRACNOSE AND ANGULAR LEAF SPOT BY PSEUDOMONAS-LACHRYMANS AND COLLETOTRICHUM-LAGENARIUM

Infection of the first true leaf of cucumber with either Pseudomonas lachrymans or Colletotrichum lagenarium systemically protected susceptible cultivars against disease caused by subsequent challenge with either pathogen. Sonicated bacterial cells, heat-killed cells, formalin-killed cells and a cell-free culture filtrate did not protect. Suspensions of bacteria swabbed onto leaf one or infiltrated into the leaf consistently induced protection against the fungus. The bacterium protected the plant against fungal inoculum containing 103 to 106 conidia ml-1. Systemic invasion by either challenge pathogen was rarely observed in protected plants. An interval of 72 to 96 h after the inducing inoculation was necessary for protection to be expressed. Protection was still evident 37 days after the initial infection. Pseudomonas pisi, P. phaseolicola and P. angulata also protected plants, but this level of protection was significantly less than that elicited by P. lachrymans. Several other bacteria tested did not elicit protection. Populations of P. lachrymans in disks of the challenged second true leaf of unprotected plants were 103 cells greater, 5 days after challenge, than those in protected plants. © 1979.