Colletotrichum gloeosporioides pelB is an important virulence factor in avocado fruit-fungus interaction

Collectotrichum gloeosporioides is an important pathogen of tropical and su btropical fruits. The C, gloeosporioides pelB gene was disrupted in the fun gus 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% high er polygalacturonase (PG) activity than the wild type. The PLB mutants exhi bited 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 additi on, these pelB mutants induced a significantly higher host phenylalanine am monia lyase activity as well as the antifungal diene, which is indicative o f higher host resistance. These results suggest that PLB is an important fa ctor in the attack of C, gloeosporioides on avocado fruit, probably as a re sult of its virulence factor and role in the induction of host defense mech anisms.