A taxonomic study of Cercospora vitis (Lév.) Sacc., the causal organism of a leaf spot disease on grapes : a thesis ... for the degree of Masterate of Agricultural Science

Abstract

A leaf spot disease of grapes caused by a dematiaceous fungus is described for the first time in New Zealand. Literature on the taxonomy of the causal organism is reviewed and reveals a pleurality of binomials that have been applied to the fungus. The main features in contention are the correct basionym, symptomatology, conidium shape and degree of conidiophore compactness. These were studied in relation to the taxonomy of the causal organism and from results obtained it was finally placed in the genus Cercospora, where the binomial becomes C. vitis; the legitimate specific epithet for the fungus. Cultural studies of the pathogen provided further supporting evidence for placement in the genus Cercospora. An apparatus for photomicrographically recording conidium ontogeny and spore germination patterns of filimentous fungi is described. Classification schemes of the Fungi Imperfecti are reviewed and all were found to have certain shortcomings with respect to the classification of the causal organism. A proposed alternative scheme is outlined. The disease does not become manifest until late in the growing season and hyphal swellings in the stomata (stomatopodia) are found to constitute the form in which the pathogen persists during a latent infection period. A disease cycle is synthesised from results of glasshouse infection experiments, field observations, and reports from the literature,