Vegetative compatibility, determined by pairing auxotrophic mutants that are unable to utilize mineral
nitrogen, was studied by means of 44 isolates of Verticillium dahliae Kleb. Thirty-seven isolates were collected from
olive in the main areas in Morocco, 3 from Algerian olives, 2 from tomato, 1 from aubergine and 1 from olive-grove soil
where Verticillium wilt was present. Approximately 475 mutants were used, allowing assignment of 34 isolates to 3
vegetative compatibility groups (VCGs). The VCGs of the remaining 10 isolates were not defined. The pathogenicity
of ten isolates was assessed by inoculating olive plants with suspensions of conidia at 105 conidia ml-1. Highly significant
differences in the pathogenic ability of the ten isolates were recorded. No relationship was found between VCGs
and pathogenicity of isolates