Graduate Thesis Or Dissertation
 

Trichoderma spp. : distribution in stumps infested with Phellinus weirii and growth and antagonism in vitro

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  • To determine which isolates will most rapidly replace Phellinus weirii in stumps and roots, Trichoderma spp. were isolated from P. weirii-infested stumps and roots, identified, and examined for growth rates and lethal effects on P. weirii in vitro. Phellinus weirii-infested Douglas-fir stumps and stump roots were sampled for microorganisms by aseptically transferring wood chips to malt agar plates. Trichoderma spp. were recovered infrequently (1.2 percent of all isolations), but their distribution suggested gradual invasion of the stumps and stump roots. Frequencies were greater in stumps of trees harvested eleven years previously than one year previously, in wood colonized than in wood not colonized by P. weirii, and in portions of roots further from the root collar. Trichoderma viride was the species most frequently isolated, followed by T. polysporum. No other Trichoderma species was isolated more than five times. Isolates collected were tested for their linear growth rates on malt agar at 5, 10, 15, 20 and 25 C. Each species responded differently to the temperatures tested and substantial variation also existed within species. Trichoderma viride and T. polysporum grew relatively rapidly at the lower temperatures, while T. harzianum and T. pseudokoningii grew rapidly at the higher temperatures. Nine of the Trichoderma spp. isolates collected in the field were tested for their ability to kill two isolates of P. weirii growing on malt agar at 10 and 20 C. This test was made possible by the development of a medium incorporating three fungicides, which inhibited Trichoderma spp. but not P. weirii. Thus it was possible to differentiate rate of lethal effect on P. weirii from rate of overgrowth by the Trichoderma sp. At 10 C, the isolates of T. viride and T. polysporum killed P. weirii significantly faster than isolates of the other Trichoderma species. Significant differences also existed in the ability of the two P. weirii isolates to withstand the killing effect of Trichoderma spp. It appears that T. viride and T. polysporum are the Trichoderma species which offer the greatest potential for reducing survival of P. weirii in the field. The ability of these species to colonize infested stumps and stump roots, to grow at temperatures normally found in the field, and to exert a lethal effect on P. weirii on artificial media has been demonstrated. Further tests are needed to thoroughly characterize antagonist and pathogen variability, and to compare results of antagonism tests on artificial media with those in the field.
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