CULTURAL AND TAXONOMIC STUDIES ON CERTAIN FUSARIA: I. MUTATION IN CULTURE

Abstract

This work represents a continuation of previous studies by the writer on the Fusarium of muskmelon wilt, with a view to determining the extent to which the cultural phenomena noted in this organism are characteristic of other Fusaria. The section Elegans is represented by 13 organisms, and the sections Liseola, Discolor, and Gibbosum by one each. Abnormal areas appearing in cultures of these organisms were investigated from the genetic viewpoint, and the results showed the larger of these to be of mutant origin. Evidence was obtained that the 'sclerotia' that appeared in cultures of some of the organisms may likewise be of mutant origin, but this was not deemed conclusive. A comparison of the properties attributed in the literature to 'sporodochia' appearing in Fusarium cultures with those of the patch mutants studied here indicates that the terms are synonymous in this case, and hence the common practice in Fusarium taxonomy of measuring 'macroconidia from sporodochia' is questioned. Since the wild types of the Fusaria studied were readily displaced in culture by mutants, it is evident that some method of maintaining the original isolates in the pure state is fundamental to a consistent taxonomy of the genus. In this connection the practice of maintaining Fusaria in tubes of sterilized soil is recommended, since experiments showed that this type of cultural treatment does not favour the loss of the wild type. A discussion is given concerning the cause of variation and the extent to which it occurs in nature.