Role of gibberellin in pathogenesis of the rice bakanae pathogen Fusarium fujikuroi

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The rice bakanae pathogen, Fisarium fujikuroi, produces gibberellin(GA) and causes overgrowth(bakanae) symptom in rice seedlings. We made GA-minus mutants from F. fujikuroi by the disruption of a GA biosynthetic gene P450-1. The GA-minus mutants did not cause bakanaesymptom and showed reduced ability to colonize rice seedlings, suggesting that GA helps the pathogen to colonize host tissue. F. fujikuroi was found to infect nonhost plants and cause bakanae symptoms, when seeds of non-host plants were planted in soil infested with the pathogen conidia. The GA-minus mutants also infect nonhost plants without symptom under the same inoculation condition. This result suggests that F. fujikuroi is an endophytic fungus with a broad host range.