Abstract
Fifteen isolates of bacteria, from potting media collected from South Australian plant nurseries and potting mix suppliers, were screened for ability to control damping-off disease caused by Pythium ultimum var. sporangiiferum. The screening was by two bioassays on seedlings of Capsicum annuum grown in a pasteurized potting medium in a glasshouse or controlled environment growth chamber. Ten isolates reduced damping-off and increased shoot weights, at least as well as the fungicide propamocarb, in both experiments. Eight isolates also reduced damping-off in seedlings of Celosia argentea in another glasshouse experiment, and all 14 isolates tested increased shoot weights, but propamocarb had no significant effect on damping-off or shoot weight. In another glasshouse experiment, four bacterial isolates were applied at five different doses to pasteurized potting medium with or without P. u. sporangiiferum. Capsicum seedlings were assayed for shoot growth and suppression of damping-off. In the presence of Pythium, only one bacterial isolate showed a dose-response in seedling survival and shoot weights, but another isolate reduced damping-off equally at all doses. In the absence of Pythium, all bacterial isolates increased shoot dry weights, but there were no responses to increased doses of bacteria. Bacillus subtilis A13 suppressed damping-off in only one of four experiments.
Published Version
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