SOIL BACTERIA SELECTED FOR SUPPRESSION OF RHIZOCTONIA-SOLANI, AND GROWTH PROMOTION, IN BEDDING PLANTS

Over 5000 bacterial isolates were obtained by dilution plating of pott ing media that were suppressive to damping-off disease caused by Rhizo ctonia solani AG 8 in seedlings of Celosia argentea. These isolates we re screened for inhibition of AG 8 in vitro, then 91 selected isolates were screened further for their ability to suppress the effects of R. solani AG 8 in seedlings of Capsicum annuum and Celosia argentea grow n in pasteurized potting medium in a glasshouse. Fourteen isolates sel ected from the above screenings then were screened similarly for suppr ession of damping-off caused by R. solani AG 4 in seedlings of Capsicu m, Celosia, Petunia and Viola. Three isolates reduced disease more con sistently than the others. B. subtilis A13, an isolate previously repo rted to control R. solani in bedding plants, did not reduce damping-of f in any host plant species. These three isolates were compared in two experiments over a range of doses for growth promotion, and suppressi on of AG 4, in Capsicum. Although there were few dose responses, when data for all dose rates were combined, all isolates increased dry weig hts of Capsicum shoots in the absence of R. solani. In one of the expe riments, all but one isolate also increased seedling survival in the a bsence of R. solani. Two bacterial isolates and the fungicide quintoze ne reduced damping-off caused by AG 4. The selected bacterial isolates exhibit potential for biological suppression of damping-off in beddin g plants in nursery potting media.