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A Virulence-Reducing Mutation in the Postharvest Citrus Pathogen Alternaria citri

September 2006 , Volume 96 , Number  9
Pages  934 - 940

H. Katoh , A. Isshiki , A. Masunaka , H. Yamamoto , and K. Akimitsu

First, second, third, fourth, and fifth authors: United Graduate School and Faculty of Agriculture, Kagawa University, Miki, Kagawa 761-0795, Japan; and fifth author: PRESTO, Japan Science and Technology Agency, Kawaguchi, Saitama 332-0012, Japan

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Accepted for publication 22 March 2006.

Alternaria citri causes Alternaria black rot, a postharvest fruit disease, on a broad range of citrus cultivars. We previously described that an endopolygalacturonase minus mutant of A. citri caused significantly less black rot in citrus fruit. To search for other essential factors causing symptoms in addition to endopolygalacturonase, a random mutation analysis of pathogenicity was performed using restriction enzyme-mediated integration. Three isolates among 1,694 transformants of A. citri had a loss in pathogenicity in a citrus peel assay, and one of these three mutants was a histidine auxotroph. Gene AcIGPD that encodes imidazole glycerol phosphate dehydratase, the sixth enzyme in the histidine biosynthetic pathway, was cloned, and the mutant containing the disrupted target gene, AcIGPD, caused less black rot.

Additional keywords: A. alternata, cell wall-degrading enzyme.

© 2006 The American Phytopathological Society