Pathogenicity and Vegetative Compatibility of Verticillium dahliae Kleb. Isolates from Olive in Morocco

Thirty-eight strains of Verticillium dahliae Kleb. from diseased olive stems originating from the most important regions of olive in Morocco, were tested by vegetative compatibility analysis to investigate their genetic diversity. Two media, water agar chlorate (WAC) and minimal medium chlorate (MMC) were used to induce the nit-mutants. The WACmediu m generated a higher frequency of nit-mutants than MMCmediu m. Based on complementarity of nit-mutants, 47% of isolates were assigned to VCG4B, 32% in VCG2 (A or B) and the 18% remaining isolates could not be grouped to any VCGs tested. These latter belonged to southern regions. Pathogenicity and aggressivity of twelve isolates from this population were assessed on four plant species which are frequently intercropped with olives. These were tomato, eggplant, cotton and pepper. All isolates were pathogenic and highly aggressive on cotton and eggplant. On cotton, the isolates from southern regions induced more severe symptoms than those from northern regions. Weak to moderate symptoms were induced by all isolates on tomato and they differed in aggressivity. No isolate was pathogenic on pepper, while four isolates from northern regions were recovered from basal stems of inoculated plants. The cor- relation between VCGs and pathogenicity on the intercropped species is discussed with regard to the regional distribution of V. dahliae population from olive.