CULTURAL AND PATHOGENIC VARIATION IN THE MUSKMELON WILT FUNGUS, FUSARIUM OXYSPORUM f. MELONIS

Abstract

The morphology of F. oxysporum f. melonis was markedly influenced especially during early growth by light, temperature, acidity, and composition of certain laboratory media. At 2 to 3 days, on an acidified peptone medium, the fungus produced macroconidia abundantly and closely similar to those found on the surface of a lesion of a wilted plant.Pigmentation, type and amount of mycelium, and sporulation of colonies varied appreciably. Interaction, indicated by "barrage lines", occurred between colonies of identical origin. Under certain cultural conditions 'wild type' isolates were morphologically indistinguishable from cultural mutants. Some mutation occurred in sterile soil culture. The morphological adaptability of the wilt fungus to cultural conditions was sufficiently great to cast doubt on the validity of delineating biologic forms and races by certain arbitrary, cultural criteria.Isolates from freshly wilted plants from different fields and from several varieties differing in susceptibility were markedly similar morphologically and pathogenically. Acceptance of the 'wild type' concept is supported.