Morphological and Physiological Differentiation among Vegetative Compatibility Groups of Verticillium dahliae in Relation to V. longisporum

Twenty-four isolates of Verticillium dahliae from var- ious geographic regions and host origins were assigned to vegetative compatibility groups (VCG) based on complementation between nitrate-non-utilizing (nit) mutants. The VCG 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 lm), and spherical microsclerotia. They exhibited polyphe- nol oxidase (PPO) activity, high sporulation rate in shake cultures, ¯uorescence on sanguinarine-amended PDA (snPDA) and excretion of dark pigment on Czapek Dox agar. The isolates assigned to VCG 4B had signi®cantly longer conidia (4.73 ‹ 0.04 lm), spherical microsclerotia and white, ¯u€y colonies due to enhanced production of aerial mycelium. They excreted only traces of dark pigment, exhibited PPO activity, did not ¯uoresce on snPDA and had limited ability to sporulate in shake cultures. Except for lacking PPO activity the only heterokaryon self-incom- patible isolate (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 lm), formed elongate microsclerotia, and only poorly sporulated in shake cultures. They did not excrete dark pigment, lacked PPO, and failed to ¯uoresce on snPDA. The results indicate a clear morphological and physiological di€erentiation not only between the two species V. longisporum and V. dahliae but also among the VCGs of V. dahliae.