| Summary: | 碩士 === 國立中興大學 === 園藝學系所 === 100 === Hosts of Rhizoctonia solani are extremely variety, and usually infected in the muggy condition cause crops “Rhizoctonia rot”. The pathogen can survive by sclerotia, by mycelia section, or by facultatively saprophyting in plant residue in soil.
After sowing and germinating, the pathogen infects root, soil-line tissue or any part of the host. Humid and warm environment enhances the rates of infection and spread, that makes it more difficult to prevent Rhizoctonia disease. This study based on the field experiment in a nursery of R. solani, and various non-chemical methods were applied to prevent the Rhizoctonia rot of pak-choi in organic cultivation practically. Twenty-four local and commercial cultivars were evaluated for resistance to Rhizoctonia rot, the percentage of damaged area of “Colors of Seasons”, “hama-minato”, and “Feng-Jing” were low. Cultivars of “Feng-Shan”, “A-Feng”, “Tai-Nong No.2”, “Native”, “Ming-Ri”, “Feng-Jing”, and “Feng-Zhen” were selected for the next planting and evaluated their yield. Compared with the previous test, the cultivar showed more tolerant, which had the stronger growth vigor. It probably escaped from the disease due to the earlier horticultural maturity. Furrow- irrigated treatment had little negative influence on the yield of pak-choi than with spray-irrigated treatment. Furrow irrigation maintained the ground of plot top arid, and a drier microclimate. Therefore, that could avoided causing favorable condition for Rhizoctonia rot ; it also prevented excessive weed growth, and that would reduced the risks of R. solani-contaminated soil falling on the plants and infecting pak-choi when weeding. Covering the plot top with peat could completely stop weed seeds to germinate, because that blocked seeds from the light. Therefore, that also prevented infecting by contaminated soil fallen on the plants when weeding. Covering with peat could prevent falling drops from splash dirt. Even when the medium splashed out, the risk of Rhizoctonia rot was still low, due to the pathogen-free medium. Covering with peat could disconnect plants from infected soil, and that protects plants from disease, seedlings especially. Further, R. solani could only cause slight damage in mature period, since the root system of mature pak-choi was vigorous. Contrast of the effects from covering-peat, tea seed pomace, and Streptomyces sp. A272 fermentation broth on Rhizoctonia rot. The covering-peat treatment showed the slightest damage, the germination rate in field was 97 %, the disease incidence was 1.67 %, and the disease severity was 0.28 %; comparatively, the maximum germination rate was 85 %, the disease incidence was 100 % and the disease severity was 48.06 % in fermentation- broth treatment; applying tea seed pomace unable to suppress the disease but promoted pre-emergence damping-off. Based on above results, furrow irrigation and covering peat were better methods to prevent Rhizoctonia rot of pak-choi. The pak-choi in covering-peat treatment still had crisp-tender mouthfeel without fibers, which was the largest plant, and the thickness of peat layer was 3cm for worked well.
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