Vegetative compatibility grouping of Verticillium dahliae from pistachio in Iran

Abstract

Sixty-nine isolates of Verticillium dahliae were recovered from pistachio (Pistacia vera) trees in the Kerman province of Iran. They were analyzed using complementation tests with nitrate-nonutilizing (nit) mutants to identify their vegetative compatibility groups (VCGs) and were compared with the four internationally recognized VCGs. Based on their ability to form heterokaryons, three local VCGs were identifi ed (using reference strains) as VCG2B (50 isolates), VCG4A (7 isolates) and VCG1 (2 isolates). Ten isolates could not be characterized with the reference strains. Thirty-four cotton isolates were also compared with the pistachio isolates using the reference strains; they were identifi ed as VCG1 (10 isolates), VCG2B (11 isolates) and VCG4A (6 isolates). (A few isolates belonged to both VCG2A and VCG2B, and a few to both VCG4A and VCG4B.) The cotton defoliating isolates (D pathotype) belonged to VCG1, and the cotton non-defoliating isolates (ND pathotype) to VCG2 and VCG4. Greenhouse pathogenicity tests of 22 isolates on cotton and okra showed that all cotton and pistachio VCG1 isolates were highly virulent and were of the defoliating pathotype (D) in both hosts. On the other hand, the isolates of VCG2B and VCG4B ranged in virulence from weakly virulent to highly virulent irrespective of their host origin. The similarity in the VCG spectrum suggests that cotton was the most likely source of Verticillium dahliae in pistachio in Iran.