1Department of Postharvest Science of Fresh Produce, Agricultural Research Organization, The Volcani Center, Bet Dagan 50250, Israel; 2Department of Plant Pathology and Microbiology, Hebrew University of Jerusalem, Faculty of Agricultural Food and Environmental Quality Sciences, Rehovot 76100, Israel; 3Department of Plant Pathology, University of California, Riverside 92521, U.S.A.; 4Department of Molecular Biology, Hebrew University, Medical School, Jerusalem 91120, Israel
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Accepted 28 March 2001.
Colletotrichum gloeosporioides is an important pathogen of tropical and subtropical fruits. The C. gloeosporioides pelB gene was disrupted in the fungus via homologous recombination. Three independent isolates, GD-14, GD-23, and GD-29, did not produce or secrete pectate lyase B (PLB) and exhibited 25% lower pectate lyase (PL) and pectin lyase (PNL) activities and 15% higher polygalacturonase (PG) activity than the wild type. The PLB mutants exhibited no growth reduction on glucose, Na polypectate, or pectin as the sole carbon source at pH 3.8 or 6.0, except for a 15% reduction on pectin at pH 6.0. When pelB mutants were inoculated onto avocado fruits, however, a 36 to 45% reduction in estimated decay diameter was observed compared with the two controls, the wild type and undisrupted transformed isolate. In addition, these pelB mutants induced a significantly higher host phenylalanine ammonia lyase activity as well as the antifungal diene, which is indicative of higher host resistance. These results suggest that PLB is an important factor in the attack of C. gloeosporioides on avocado fruit, probably as a result of its virulence factor and role in the induction of host defense mechanisms.
© 2001 The American Phytopathological Society