Cultivar resistance to anthracnose disease of cowpea (Vigna unguiculata (L.) walp.) caused by Colletotrichum destructivum O'Gara

The infection process of Colletotrichum destructivum, a hemibiotrophic anth racnose fungus, was studied by light microscopy in two cowpea (Vigna unguic ulata) cultivars which differ in disease reaction type. Large, multilobed, intracellular infection vesicles, followed by necrotrophic, radiating, seco ndary hyphae were produced in tissues of the susceptible cv. IT82E-60. In t he resistant cv. TVx 3236, both the production of appressoria and their mel anisation were impaired, resulting in reduced penetration. Where penetratio n occurred, the initially-infected epidermal cells underwent a hypersensiti ve response, restricting the growth of multilobed vesicles and thereby bloc king the destructive necrotrophic phase of disease development. The phytoal exins kievitone and phaseollidin accumulated earlier and more rapidly in st em tissues of the resistant cultivar, associated with the appearance of del imited, necrotic spots on inoculated surfaces. In contrast, delayed and slo wer accumulation of these compounds occurred in the compatible interaction, together with the development of typical spreading, water-soaked, anthracn ose lesions.