Vegetative compatibility and pathogenicity of Verticillium dahliae Kleb. isolates from olive in Israel

Fifty-two isolates of Verticillium dahliae from olive trees grown at different locations in Israel were assigned to vegetative compatibility groups (VCGs), using nitrate non-utilizing ( Nit) mutants. A higher frequency of nit1/nit3 mutants (95%) was obtained compared with NitM (5%), with 81% of the isolates being assigned to VCG4B and 19% to VCG2A. The pathogenicity of 14 randomly selected isolates ( seven of each VCG) was tested on olive twigs (cv. Picual) and tomato. VCG4B and VCG2A isolates were similarly aggressive on olive. However, VCG2A isolates were more aggressive on tomato ( line 139) than the VCG4B isolates as indicated by a higher colonization index.