MOLECULAR VARIATION AND SUB-SPECIFIC GROUPINGS WITHIN VERTICILLIUM-DAHLIAE

On the basis of molecular variation, as revealed by RFLPs, isolates of both Verticillium dahliae and V. alboatrum were divided into two major groups, designated A and B in V. dahliae and L and NL in V. alboatrum. There was very limited variation within the groups. A few isolates of V. dahliae did not fall consistently into either of the two groups; when tested with a range of the probe/enzyme pairs which distinguished the groups, these isolates showed combinations of the polymorphisms which distinguished A and B (i.e. an isolate of this type appeared like group A isolates with some pairs and like group B isolates with others). No isolates sharing characters from the L and NL groups were seen in V. alboatrum. In V. alboatrum the groups correlated with original hosts of the isolates (all L isolates being originally from lucerne; isolates from all other hosts were in NL). There was no clear correlation between grouping and original host in V. dahliae but the relative frequency of occurrence of isolates in the groups did vary with host. Cellulase isozyme pattern was correlated with fungal species and in V. dahliae with isolate group; in V. alboatrum most isolates (whether from the L or NL group) gave an identical pattern, but two of the four L group isolates tested gave a second, distinct pattern.