Vegetative compatibility groups of Verticillium dahliae in Israel: Their distribution and association with pathogenicity

A collection of 565 isolates of Verticillium dahliae, recovered between 199 2 and 1997 from 13 host plant species and soil at 47 sites in Israel, was t ested for vegetative compatibility using nitrate-nonutilizing (nit) mutants . Three vegetative compatibility groups (VCGs) were found and identified as VCG2A (28 isolates), VCG2B (158 isolates), and VCG4B (378 isolates) by usi ng international reference strains. One isolate was heterokaryon self-incom patible. Of the VCG2B isolates, 92% were recovered from the northern part o f Israel and 90% of VCG4B isolates were recovered from the south, with some overlap in the central region. Isolates of the minor group VCG2A were geog raphically scattered among the two major VCGs. Isolates of the same VCG res embled one another more than isolates from different VCGs based on colony a nd microsclerotial morphology, temperature responses, and, partially, patho genicity. Different pathotypes were defined among 60 isolates tested, using cotton (cv. Acala SJ-2) and eggplant (cv. Black Beauty) as differentials. All isolates in VCG2A and 86% of the isolates in VCG4B, irrespective of the ir origin, induced weak to moderate symptoms on cotton and moderate to seve re symptoms on eggplant and were similar to the previously described cotton nondefoliating pathotype. In contrast, all cotton isolates in VCG2B caused severe foliar symptoms, stunting, and often death, but little or no defoli ation of inoculated cotton plants. These were defined as a cotton defoliati ng-like pathotype and induced only weak to moderate symptoms on eggplant. W e concluded that vegetative compatibility grouping of V. dahliae in Israel is closely associated with specific pathogenicity and other phenotypic trai ts.