Morphological and physiological differentiation among vegetative compatibility groups of Verticillium dahliae in relation to V-longisporum

Twenty-four isolates of Verticillium dahliae from various geographic region s and host origins were assigned to vegetative compatibility groups (VCG) b ased on complementation between nitrate-non-utilizing (nit) mutants. The VC G assignment was associated with clearly distinguishable morphological and physiological characteristics. Most isolates of VCG 2B produced deep black colonies, small conidia (3.62 +/- 0.02 mum), and spherical microsclerotia. They exhibited polyphenol oxidase (PPO) activity, high sporulation rate in shake cultures, fluorescence on sanguinarine-amended PDA (snPDA) and excret ion of dark pigment on Czapek Dox agar. The isolates assigned to VCG 4B had significantly longer conidia (4.73 +/- 0.04 mum), spherical microsclerotia and white, fluffy colonies due to enhanced production of aerial mycelium. They excreted only traces of dark pigment, exhibited PPO activity, did not fluoresce on snPDA and had limited ability to sporulate in shake cultures. Except for lacking PPO activity the only heterokaryon self-incompatible iso late (HSI) was similar to VCG 4B. Ten isolates of Verticillium longisporum from cruciferous hosts did not produce nit mutants. They had clearly longer conidia (7.41 +/- 0.05 mum), formed elongate microsclerotia, and only poor ly sporulated in shake cultures. They did not excrete dark pigment, lacked PPO, and failed to fluoresce on snPDA. The results indicate a clear morphol ogical and physiological differentiation not only between the two species V . longisporum and V. dahliae but also among the VCGs of V. dahliae.