| Summary: | 碩士 === 國立中興大學 === 植物病理學系所 === 103 === Fusarium fujikuroi is the causal agent of bakanae disease, usually resulting in severe yield loss. It has long been considered that the infection of seed is the major cause of this disease. Symptoms occur not only on seedling stage, but also on tillering and heading stages. It is very likely that the symptoms of tillering and heading stage are from soil inoculum. The aim of this study is to investigate the correlation between soil inoculums and disease occurrence on tillering and heading stages, and to realize the disease process after seeds were infected. To evaluate the ability of survival of pathogens, modified selective medium was established, and marked nit mutants were developed. The results suggest that the soil inoculum do have the ability to cause disease, although the incidence is low. Inoculated seeds lead to 100% diseased seedlings, among which some may appear healthy in later stage (some of them may appear diseased again), some may stay diseased continuously. With regard to the production of gibberellins of different isolates, a bioassay method was designed. A dwarf mutant line of rice was used to quantify the production of gibberellins.
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