COMPOST AND COMPOST WATER EXTRACT-INDUCED SYSTEMIC ACQUIRED-RESISTANCE IN CUCUMBER AND ARABIDOPSIS

A biocontrol agent-fortified compost mix, suppressive to several disea ses caused by soilborne plant pathogens, induced systemic acquired res istance (SAR) in cucumber against anthracnose caused by Colletotrichum orbiculare and in Arabidopsis against bacterial speck caused by Pseud omonas syringae pv. maculicola KD4326. A peat mix conducive to soilbor ne diseases did not induce SAR. The population size of P. syringae pv. maculicola KD4326 was significantly lower in leaves of Arabidopsis pl ants grown in the compost mix compared to those grown in the peat mix. Autoclaving destroyed the SAR-inducing effect of the compost mix, and inoculation of the autoclaved mix with nonautoclaved compost mix or P antoea agglomerans 278A restored the effect, suggesting the SAR-induci ng activity of the compost mix was biological in nature. Topical spray s with water extract prepared from the compost mix reduced symptoms of bacterial speck and the population size of pathogenic KD4326 in Arabi dopsis grown in the peat mix but not in the compost mix. The peat mix water extract applied as a spray did not control bacterial speck on pl ants grown in either mix. Topical sprays with salicylic acid (SA) redu ced the severity of bacterial speck on plants in the peat mix but did not further reduce the severity of symptoms on plants in the compost m ix. The activity of the compost water extract was heat-stable and pass ed through a 0.2-mu m membrane filter. beta-1,3-Glucanase activity was low in cucumber plants grown in either mix, but when infected with C. orbiculare, this activity was induced to significantly higher levels in plants grown in the compost mix than in plants grown in the pear mi x. Similar results were obtained for beta-D-glucuronidase (GUS) activi ty driven by a PR2 (beta-1,3-glucanase) gene promoter in transgenic Ar abidopsis plants grown in the compost or peat mix. GUS activity was in duced with topical sprays of the compost water extract or SA in plants not inoculated with the pathogen, suggesting that compost-induced dis ease suppression more than likely involved the potentiation of resista nce responses rather than their activation and that compost-induced SA R differed from SAR induced by pathogens, SA, or compost water extract .