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A study of the physiology and strains of Ophiostoma fimbriatum (E&H) Nann Madhosing, Clarence

Abstract

The fungus Ophiostoma fimbriatum (E & H) Nann, though exceptionally rare in northern climates, is fairly widespread in tropical and sub-tropical areas of the world causing diseases on many species of plants. The disease producing capabilities of the fungus have become a major economic problem in the growth and storage of sweet potatoes (Ipomoea batatas (L.) Lam) in the southern parts of the United States. The organism is interesting from the point of view that it produces, very readily on sweet potato dextrose agar, two types of asexual or vegetative spores and the perfect stage with the perithecia containing ascospores. Several strains of the fungi have been isolated from natural habitats. This work deals, in general, with a study of the gross morphology of this ascomycete and some observations on the nuclear apparatus of the resting and germinating conidia. More specifically, this study treats with certain factors in nutrition which affect the physiology in such a way that the growth and sporulation characteristics of the organism are altered. Since several strains of 0. fimbriatum have been isolated naturally it is thought that these must have been derived from mutant changes occurring in an original "wild" form which was propagated to more susceptible varietal hosts. As a result, studies are undertaken in an attempt to induce changes in an original culture by adopting artificial mutagenic methods. A pathogenicity experiment is done on sweet potato blocks in the laboratory to ascertain the relative degree of virulence between the new-formed strains. This work shows that the cultural characteristics and reproductive behaviour of this fungus could be modified by specific variations in the culture medium. It is shown among other things, that copper, in the role of a micro-nutrient, plays a definite part in the manifestation of sexuality and in the development of pigmentation in the organism. "Mutations" are produced by using X-irridiation and ultra-violet rays as inductive agents. Many of the new-formed "mutants" are unstable and back mutation to the original "wild" type is common.

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