INFECTION PROCESS AND HOST-RANGE OF COLLETOTRICHUM-CAPSICI

The pathogenicity, host range and infection process of three isolates of Colletotrichum capsici, from cowpea (Vigna unguiculata), bean (Phas eolus vulgaris) and betle vine (Piper betle), are described. The locat ion and morphology of infection hyphae of C. capsici within hypocotyls of cowpea were investigated by light, transmission and cryo-scanning electron microscopy. All isolates attacked a similar range of legumes, but other legumes were resistant. Wounding increased their pathogenic ity on susceptible hosts. All susceptible tissues were completely rott en within 8-10 days, with acervuli present over the entire surface of the hypocotyls. Initial infections occurred after production of appres soria. Infection hyphae penetrated cuticles and initially grew beneath the cuticle in the anti- and periclinal walls of epidermal cells caus ing extensive wall degradation. Subsequently, hyphae grew in and destr oyed the walls of underlying cortical cells. This was associated with extensive death of adjacent cells, which led to production of water-so aked lesions. When tissues were extensively rotted, hyphae entered scl erenchymatous fibres by direct growth through their walls. Freeze-subs tituted preparations revealed vesicles and plasmatubules in infection hyphae. It is proposed that successful pathogenesis is based on suppre ssion of host defence responses through rapid killing of infected tiss ues. A comparison of this infection strategy with those of other Colle totrichum species indicates that knowledge of a pathogen's infection p rocess may be used to predict whether it has a narrow or wide host ran ge.