Abstract

A detailed account of symptoms produced by Colletotrichum gloeosporioides on susceptible and resistant cultivars of yam (Dioscorea alata) in Solomon Islands is given. A superficial blackening of upper leaf surfaces of some cultivars is unusual and worthy of further study. In pathogenicity tests with isolates of C. gloeosporioides from various sources, those that were virulent on D. alata were all from D. alata except one from D. esculenta and one from Cucumis sativus but only nine of 30 isolates from D. alata were virulent on this host. Since all four isolates of the yam pathogen tested on D. nummularia and D. trifida were virulent, it is inappropriate to retain the epiphet f. sp. alatae proposed by earlier authors. Considerable variation in cultural morphology existed among virulent isolates, the only consistent character being production of dark pigment, although this was also produced by some saprophytic isolates. Most reisolations of C. gloeosporioides from lesions resulting from inoculation yielded isolates identical with the original inoculum but also some reisolates had a different morphology.