Diversity among isolates ofVerticillium lecanii as expressed by DNA polymorphism and virulence towardsBemisia tabaci

Thirty-six isolates ofVerticillium lecanii andVerticillium sp. were taken from different hosts (both insects and rusts) and geographical locations. The isolates were analyzed for genomic variability, as expressed by random amplified polymorphic DNA (RAPD), in relation to virulence onBemisia tabaci. Virulence on larvae ofB. tabaci within these isolates ranged from 0% to 83%. RAPD analysis was performed employing two different arbitrary decamer primers and the calculated similarity coefficients were subjected to cluster analysis using the unweighted average linkage (UPGMA) algorithm. The dendrograms obtained with each of the two primers were identical. Eight cluster groups and three unclustered isolates were obtained by selecting a similarity level of 80%. The amplification pattern of DNA obtained by RAPD for the various isolates suggested thatV. lecanii is a highly diverse species. No correlation could be established between virulence and either RAPD polymorphism of the fungal isolates or the insect host from which they were isolated. Generally, no correlation could be established between the clustering ofV lecanii strain and geographical location although a limited number of strains obtained from Russia and Georgia were assembled in the same cluster and those from Kazakhstan were clonal.