A quantitative bioassay for determining low numbers of microsclerotia of <i>Verticillium dahliae</i> in field soils

Abstract

The relationship between inoculum density and the number of colonies of Verticillium dahliae Kleb./unit length of root from plants growing in naturally infested soils is shown to be linear. The evidence supports the contention that the propagules giving rise to these colonies are microsclerotia or small groups of microsclerotia embedded in fragments of plant tissue. Thus the colonies growing on plant roots are a quantitative measure of the number of these propagules in soil. The data show that plant roots are an extremely sensitive trap and can be used to measure low numbers of microsclerotia.