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A non-pathogenic Fusarium oxysporum W5 effectively controls “Bakanae” disease by competing with the pathogen on rice flowers and seedlings

Hiroki Saito: Tokyo Univ Agric & Tech(TUAT)

<div>“Bakanae” (means foolish seedling), caused by <em>Fusarium fujikuroi</em>, is one of the most important diseases of rice (<em>Oryza sativa</em>) in Japan. Though chemical fungicides (e.g. ipconazole) are effective in the control of “Bakanae” at present, the future emergence of fungicide resistant strain of the pathogen is concerned. Therefore, we tried to establish a novel biocontrol method of “Bakanae” using non-pathogenic <em>Fusarium</em>. We obtained 70 isolates of non-pathogenic <em>Fusarium</em> spp. from the rice plants in “Bakanae” outbreak fields in Japan. We selected a non-pathogenic <em>F. oxysporum</em> W5 as a candidate of biocontrol agent for “Bakanae”. W5 presented clear “Bakanae” control activity in the rice plants generated from the seeds obtained from the flower treated with W5 bud cell suspension when flowering. Thus, we consider that spraying rice flower with W5 is an effective method of “Bakanae” control. Subsequently, we observed the dynamics of <em>F. fujikuroi</em> expressing RFP and W5 expressing eGFP on the rice plant. Compared to the single infection of <em>F. fujikuroi</em>, the frequency of <em>F. fujikuroi</em> fluorescence was remarkably reduced under the presence of W5. Interestingly, the fluorescence of W5 was not affected much by the presence of <em>F. fujikuroi</em>. Additionally, W5 did not inhibit the growth of <em>F. fujikuroi</em> on dual culture assay on potato dextrose agar (PDA). These results suggested that W5 competes with <em>F. fujikuroi</em> for nutrition and/or space on the rice plant tissues.</div>