Comparative study of genetic diversity and pathogenicity among populationsof Verticillium dahliae from cotton in Spain and Israel

Genetic diversity and phenotypic diversity in Verticillium dahliae populati ons on cotton were studied among 62 isolates from Spain and 49 isolates fro m Israel, using vegetative compatibility grouping (VCG), virulence and mole cular assays. In Spain, defoliating V. dahliae isolates (D pathotype) belon g to VCG1, and non-defoliating isolates (ND) belong to VCG2A (often associa ted with tomato) and VCG4B (often associated with potato). The D pathotype was not identified in Israel. The ND pathotype in Israel is comprised of VC G2B and VCG4B. Isolates in VCG2B and VCG4B ranged in virulence from weakly virulent to highly virulent. The highly virulent isolates induced either pa rtial defoliation or no defoliation. Virulence characteristics varied with inoculation method and cotton cultivar. Highly virulent isolates from Israe l were as virulent as D isolates from Spain under conditions conducive to s evere disease. The D pathotype is pathologically and genetically homogeneou s, whereas the ND pathotype is heterogeneous with respect to virulence, VCG , and molecular markers based on single-primer RAPD and on PCR primer pairs .