Isolates of Verticillium nigrescens and V. tricorpus were obtained from pot
ato, cotton, eggplant, weeds and field soil in Israel. Chiorate-resistant n
itrate-nonutilizing (nit) mutants were generated from each isolate and used
in complementation (heterokaryon) tests. Eleven vegetative-compatibility g
roups (VCGs) were found among 19 V. nigrescens isolates from nine sites, an
d nine VCGs among 26 isolates of V. tricorpus from eight sites. Optimal gro
wth temperature was 24-27 degrees C for V. nigrescens and 24 degrees for V.
tricorpus. None of the isolates caused leaf symptoms or stunting in inocul
ated eggplant and cotton seedlings, while severe symptoms were caused by V.
dahliae. Colonization of inoculated seedlings by V. nigrescens and V. tric
orpus occurred primarily in roots and hypocotyls, while V. dahliae heavily
colonized upper stems as well.