| Summary: | 碩士 === 國立臺灣大學 === 植物醫學碩士學位學程 === 106 === Brown root rot disease, caused by Phellinus noxius, is one of the most destructive tree diseases that has raised much public attention. Trees infected with P. noxius do not show obvious symptoms at early stages. Usually when brown root rot is diagnosed, it is too late for disease control. The methods currently applied for brown root rot control include soil fumigation using Dazomet and drench treatment using systemic fungicides. However, misuse of chemicals may cause environmental pollution and harmful effects to non-target organisms. In vitro experiments by Schwarze et al. (2012) and Tang et al. (2016) showed that Trichoderma sp. can inhibit the growth of P. noxius and prevent wood blocks from P. noxius degradation. Schubert et al. (2008) also found that application of Trichoderma sp. can reduce the infection of wood decay fungi through wounds. In this study, we first tested antagonistic activity of 4 different Trichoderma isolates against 4 different P. noxius isolates by dual culture on 1/2 potato dextrose agar (PDA) medium. Inoculation of Trichoderma and/or P. noxius isolates on wood blocks of Ficus microcarpa showed that pretreatment with Trichoderma significantly reduced the loss of dry weight caused by P. noxius. A single Trichoderma isolate showing strong and stable antagonistic activity, T. asperellum TA, was further confirmed to be effective in delaying the wilting of P. noxius 2248–inoculated loquat seedlings (Eriobotrya japonica) in the pot assay. Both wood block and pot assays suggested that better biocontrol efficiency can be achieved by applying Trichoderma sp. prior to the infection of P. noxius. Loquat roots inoculated with P. noxius 2248及T. asperellum TA were examined by surface sterilization and cultivation on selective media. The isolation rates of P. noxius were correlated with the wilting rates of loquat seedlings in different treatments. Low isolation rates of Trichoderma were observed, even from the roots only treated with T. asperellum TA (11.1% of coarse roots and 4.2% of fine roots), indicating weak colonization ability of T. asperellum TA in loquat roots. To provide more options for chemical control, as well as to evaluate the feasibility of combining Trichoderma and fungicides for disease management, 18 systemic fungicides that are relatively lower toxic were tested for inhibition of the mycelial growth of 4 Trichoderma isolates and 4 P. noxius isolates on PDA amended with individual chemical. Cyproconazole and epoxiconazole were effective in suppressing P. noxius at 1 ppm, and Trichoderma had lower sensitivity to triadimefon and mepronil. These findings provide new insights into the control of brown root rot.
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