Combinations of Fungal Antagonists for Biological Control ofArmillariaRoot Rot of Strawberry Plants

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Abstract
In a pot experiment with strawberry plants (cv. Cambridge Favourite), two isolates (Th1 and Th2) of Trichoderma harzianum were tested individually and in combination for their efficacy against the root rot pathogen Armillaria mellea. Similarly, an effective isolate of Dactylium dendroides, the ‘Shi-itake Pathogen’ (SP), was combined with isolates of T. harzianum, T. viride, T. hamatum and Chaetomium olivaceum for the same purpose. Isolate Th2 performed better alone than in combination with isolate Thl, protecting 75% of the plants from death during the experiment lasting 413 days. None of the plants treated with Thl alone or Thl and Th2 together survived until the end of the experiment. The presence of SP had a significant (p < 0.05) effect on the survival of the plants. The median survival time in the presence of SP was 299.5 days compared with 206.0 days in its absence. At the end of the experiment, which lasted 534 days, 41.7% of the plants treated with SP survived compared with only 16.7% when not treated with the antagonist. The plants also had significantly more living leaves and higher health scores when SP was used. The combination-antagonists did not differ significantly from controls in suppressing the disease and thus enhancing the survival of the plants. The interaction of SP with the combination-antagonists was significant. It improved the efficacy of the other antagonists tested except T. hamatum isolate Thaml and C. olivaceum isolate Co. All the plants treated with T. harzianum isolates Th2 and Th23 or T. viride isolate Tv3 alone died by the end of the experiment, while 50% of them survived when treated with a combination of any of the antagonists and SP. T. hamatum isolate Thaml protected 75% of the plants alone and only 50% in combination with SP.