Spontaneous Occurrence of the Sekiguchi Lesion in Two American Rice Lines: Its Induction, Inheritance, and Utilization

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Abstract
Occurrence of the Sekiguchi lesion in rice is conditioned by a single recessive gene and can be induced either by infection with Bipolaris oryzae and Pyricularia oryzae, or by exposure to certain chemical agents. Rice plants with Sekiguchi lesions were found both as naturally occurring mutants and in X2 populations from 137Cs-irradiated seed. The lesions first appear on leaves and sheaths as gray water-soaked spots that turn orangish brown and become zonate as they enlarge, coalesce, and finally occupy the entire plant. Histopathological observations suggest that the Sekiguchi lesion represents a flaw in the biological mechanisms that normally regulate the hypersensitive response of rice to invasion by potential pathogens. Rice lines having the Sekiguchi lesions were used successfully as spreaders to increase inoculum levels of B. oryzae in field studies of brown leaf spot of rice.