| Summary: | 碩士 === 國立中興大學 === 土壤環境科學系所 === 104 === Tomato is one of the most important vegetable crops in the world. However, Fusarium oxysporum f. sp. lycopersici, the causal agent of Fusarium wilt, causes severe economic losses in commercial tomato production. When tomato plants show typical symptoms of Fusarium wilt, it is difficult to control the disease. This study aimed to evaluate the possibility of using Trichoderma sp. as a biocontrol agent to control Fusarium wilt and to determine the effect of tomato seedlings inoculated with the biocontrol agent on nutrient uptake. Trichoderma species were isolated from field soils and commercial composts and identified using morphological characteristics and phylogenetic analyses. Among the 56 Trichoderma isolates collected, isolate CHF 78 showed a considerably antagonistic activity against F. oxysporum f. sp. lycopersici. The physiological characteristics of CHF 78 were further analyzed, and various carrier materials were used to induce the sporulation of the isolate. Moreover, tomato seedlings grown in peat, quartz sand, and a field soil were inoculated with CHF 78 to determine its biocontrol efficacy against the pathogen. The radial growth inhibition percentage of F. oxysporum f. sp. lycopersici by CHF 78 was up to 73.5%. Based on the phylogenetic analyses of the internal transcribed spacer (ITS) region and translation elongation factor-1α (TEF1α) gene, CHF 78 was named as Trichoderma asperellum. The spores of CHF 78 could germinate after heating at 40℃ for 7 days. In addition, CHF 78 had ability to solubilize phosphate, secrete siderophores, release indole-3-acetic acid (IAA), and produce cellulase, chitinase, urease, and protease. Spent mushroom wastes and rice bran could significantly induce the sporulation of CHF 78 because its spore concentration was maintained at a concentration of 109 spores/g for 6 weeks, suggesting that these two agricultural wastes could be used to culture CHF 78. Tomato seedlings grown in a field soil and pre-inoculated with CHF 78 had a numerical reduction of disease severity by 2.90%. However, pre-inoculation of tomato seedlings with CHF 78 resulted in a significantly lower level of disease severity, which was reduced by 55.4 in peat and 56.2% quartz sand, respectively. Regression analysis suggested that there was a significant relationship between disease severity of Fusarium wilt and the uptake of potassium or calcium in tomato plants, with higher coefficients of determination for the experiments performed in all the three growing media. In summary, T. asperellum CHF 78 may be used as a biocontrol agent of Fusarium wilt of tomato.
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