Implications of Genetic/Molecular Evidence with Respect to Virulence/Avirulence of Fungal Wilt Pathogens

Abstract

This review deals with the genetics of virulence/avirulence in Verticillium albo-atrum, V. dahliae and Fusarium oxysporum f. sp. lycopersici. Any such study must take account of the complex interactions occurring between the vascular wilt fungus and its host; these involve different sequential events, host cells of distinct types and morphological/physiological changes in the pathogen, all within a single infection cycle. It is also necessary to draw on our rapidly developing understanding of the molecular mechanisms underlying race-specific and ‘generalised’ resistance in host/parasite relationships generally and to see how far we can ‘fit’ these in to the available information for the vascular wilt fungi with their unique and complex ‘lifestyle’. The term pathogenicity is used here to denote the general capacity of a population of individual isolates of a pathogen (comprising a species, forma specialis or ‘strain’), to cause disease symptoms in a particular host. Virulence is used to indicate quantitatively the ability of a particular isolate or entity of a pathogen, to cause disease in a susceptible host under standard conditions.