In this research 40 isolates of Fusarium oxysporum f.sp. tuberosi, the causal agent of three important diseases of potato in field or storage namely, Fusarium dry rot, Wilt and Stem end-rot were used for determination of Vegetative Compatibility Groups (VCG). At first nit mutants were generated on chlorate media and then nit mutants were assigned to different phenotypic classes on the basis of their growth on media containing one of the five different nitrogen sources ( NaNO3, NaNO2, Hypoxanthine, Ammonium nitrate and Uric acid). 49.9% of nit mutants were classified to nit1, 30.3% to nit3 and 15.9% to NitM phenotypic classes. For complementation tests and determining VCGs , all NitM mutants of every isolate were paired with nit1 or nit3 mutants of other isolates. Generating of dense aerial growth in touch place of colonies after 7 to 14 days shows vegetative compatibility. On this basis eight VCGs were determined as VCG1, VCG2, VCG3, VCG4, VCG5, VCG6, VCG7 and VCG8. VCG1, VCG2 and VCG3 belonged to wilt isolates. VCG4 contains isolates that belonged to wilt and stem end rot. VCG5 having just one isolate that belonged to Stem end rot. VCG6, VCG7 and VCG8 contained fusarium dry rot isolates. Results show the possibility of some genetical homology between wilt and stem end rot isolates. There was not any relationship found between geographical distribution and VCGs.
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