Versatility of fungal and bacterial isolates for biological control of damping-off disease caused by Rhizoctonia solani and Pythium spp.

Two fungal and three bacterial isolates were tested for efficacy in control of damping-off disease and survival under a range of conditions. In two experiments with Capsicum annuum seedlings in pasteurized potting medium at 25 degrees C, two binucleate Rhizoctonia isolates (BNR1 and BNR2) were more effective against Rhizoctonia solani anastomosis group 4 (AG 4) than the bacteria, Bacillus amyloliquefaciens, and two isolates of Pseudomonas putida. In in vitro tests, all five. biocontrol isolates grew best at 16-37 degrees C and survived 2 days at 3 degrees C, but only B. amyloliquefaciens survived at 42 degrees C. BNR1 suppressed damping-off caused by Pythium ultimum var, sporangiiferum in Brussels sprouts grown in pasteurized patting medium at 15 degrees C. Both isolates of binucleate Rhizoctonia, but not the three bacterial isolates, completely controlled damping-off caused by P. irregulare in seedlings of C. annuum in the same potting medium in a glasshouse. In various experiments with several commercial nursery potting media, both isolates of binucleate Rhizoctonia suppressed damping-off caused by P. ultimum var. sporangiiferum or R. solani AG 4 and promoted shoot growth in the presence of R. solani AG; 4, Low doses of both binucleate Rhizoctonia isolates were effective against R, solani AG 4 in a pasteurized potting medium. BNR1 survived saprophytically in pasteurized potting medium for at least 13 months. These results show that the two binucleate Rhizoctonia isolates control several fungal pathogens and are effect;ive at low doses, at low temperatures on host plants, and in various soils. They have potential for commercial development for application to bedding plants. (C) 1999Academie Press.