Interactions among Gaeumannomyces graminis var. tritici, Trichoderma koningii, and soil bacteria

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Abstract
Interactions among Gaeumannomyces graminis var. tritici, Trichoderma koningii, and soil bacteria were studied in vitro and in soils suppressive and conducive of the saprophytic growth of G. graminis var. tritici. Fifty-four percent of bacteria isolated from the suppressive soil and 10% from the conducive soil were antagonistic to G. graminis var. tritici in vitro. The reduction in the growth of T. koningii in vitro by metabolite(s) produced in pure culture by soil bacteria was 14 and 28% for the bacteria isolated from the suppressive and conducive soil, respectively. Metabolite(s) produced by T. koningii in pure culture inhibited the growth in vitro of 8 and 65% of the bacteria isolated from the suppressive and conducive soils, respectively. All isolates of Trichoderma tested produced metabolite(s) that inhibited growth of G. graminis var. tritici in pure culture. The metabolite(s) produced by one isolate of T. koningii inhibited growth of all isolates of Trichoderma in vitro. Trichoderma koningii suppressed saprophytic growth of G. graminis var. tritici in irradiated conducive soil in the absence but not in the presence of bacteria isolated from the same soil. The results suggest that the suppressive soil may be more suppressive of the saprophytic growth of G. graminis var. tritici and less suppressive of the growth of T. koningii than the conducive soil.