INFECTION PROCESS AND HOST SPECIFICITY OF A COLLETOTRICHUM SPECIES CAUSING ANTHRACNOSE DISEASE OF COWPEA, VIGNA-UNGUICULATA

The morphology, pathogenicity and host specificity of a strain of C. lindemuthianum (I57), causing anthracnose on cowpea were studied. Strain I57 exhibited a novel hemibiotrophic infection process which resulted in production of water-soaked lesions in all tissues of cowpea seedlings. Biotrophic infection hyphae formed in viable epidermal cells: the hyphae were large and became highly branched, but remained within the initially-infected epidermal cells. After 20–30 h, the infected epidermal cells died and soon afterwards the surrounding uninfected cells also died. When the initially-infected epidermal cells had been extensively colonized, thinner sparsely branched hyphae grew into and through the surrounding tissues, producing lesions with large numbers of acervuli on their surfaces. This type of infection process has not previously been described for a species of Colletotrichum. When inoculated on to hypocotyls of bean (Phaseolus vulgaris) and several other legumes, I57 caused rapid hypersensitive death of single epidermal cells. A comparison of strain I57 with isolates of C. lindemuthianum that attack bean, but not cowpea indicated that their culture morphologies, mycelial growth rates, modes of conidial germination, infection processes and host specificities were different. These results suggest that the identification of strain I57 as a form of C. lindemuthianum should be re-examined. © 1990, British Mycological Society. All rights reserved.