Growth of the mycoparasitic fungus Verticillium biguttatum from different geographical origins at near-minimum temperatures

Abstract

Sclerotia ofRhizoctonia solani collected from potato tubers from different countries were assayed for the presence of mycoparasites. Among the mycoparasites observedVerticillium biguttatum predominated. Its geographical distribution was not restricted to certain latitudes or soil types;V. biguttatum occurred worldwide in potato fields.

The minimum growth temperature of 57V. biguttatum isolates was found to be in the narrow range from 10 to 13°C, irrespective of their geographical origin. A non-linear logistic growth model was used to describe the radial growth onRhizoctonia mycelium and nutrient agar plates. At near-minimum temperature the maximum colony radii varied considerably; they were up to 3.8 times that of the reference isolate M73. Based on parameter values for logistic growth, fast-and slow-growing isolates could be distinguished. Although the growth properties ofV. biguttatum isolates from different locations varied, the presence of fast- and slow-growing isolates was not restricted to particular areas and both types could be found in the same field. However, bioassays with selected fast- and slow-growing isolates do not support the assumption that growth at near-minimum temperatures is a relevant criterion for screening isolates ofV. biguttatum in terms of effectiveness for biological control ofR. solani.