MORPHOLOGY OF THE SWEET POTATO SCAB FUNGUS (Sphaceloma batatas Saw.)

Abstract

Specimens of sweet potato stem and foliage scab were examined microscopically and the causal fungus was cultured in agar media. Two types of conidia were observed, namely: the ovoid or oblong-elliptical designated as macroconidia with an average size of 6.99 x 12u and the minute and spherical referred to as microconidia with an average size of 3.22 x 1.97u. Some microconidia were borne on conidiophores while others lacked well-defined conidiophores whether on host tissues or in culture media. The origin of microconidia was not definitely established in this study. The macroconidia were made to germinate on various liquid media at different time periods. Germination was high in the sweet potato leaf exudate. The conidia enlarged and formed cross walls in 4 hr, formed germ tube and additional septa in 6 hr, branched in 48 hr and as branching became more developed, the hyphae thickened and became constricted in 68 hr.