AN INTEGRATED APPROACH TO THE TAXONOMY OF THE GENUS VERTICILLIUM

The taxonomic relationship among 64 isolates of the genus Verticillium was investigated using a range of morphological, physiological and biochemical characters with particular reference to V. lecanii. Forty-five isolates pertaining to the V. lecanii complex were compared, including isolates from arthropods (entomopathogens), rust fungi (hyperparasites) and 'saprophytic' sources. Other Verticillium species from invertebrate, fungal and plant hosts were included in the study to explore relationships within the genus. By analysing 41 characters, similarities were calculated between isolates using Gower's coefficient, and dendrograms were derived by average linkage clustering. Six cluster groups were delimited: V. lecanii isolates (7), mostly from homopteran insects; hyperparasitic isolates (3), including one of V. psalliotae, from rusts; V. lecanii isolates (18) mainly from insects of UK origin; V. lecanii isolates (7) from coffee rust; V. lecanii isolates (11) from scale insects, predominantly tropical; and two isolates of V. alboatrum. The remaining 16 isolates, mostly from Cordyceps and Torrubiella infections of tropical forest arthropods, did not fit into any cluster group and all probably represent undescribed anamorphs. A similar pattern was obtained when the electrophoretic properties of catalase isoenzymes were compared. Twelve catalase bands were identified. The taxonomic significance of these findings is discussed.