One hundred and eighty eight nitrate non-utilizing (nit) mutants were recovered from 52 isolates of F. oxysporum f.sp. cumini(F.O.C.) cultured on three media: potato-dextrose chlorate (PDC), potato sucrose chlorate (PSC) and minimal chlorate (MMC). Out of these mutants, 159, 17 and 12 were nit 1, nit M and nit 3, respectively. The majority (80.32 %) of nit mutants were generated on PSC medium compared with 14.89 and 4.78 % on PDC and MMC, respectively. Not all three phenotypes classes were recovered from all isolates and the frequency of occurrence of each mutant type varied from isolate to another. “nit" mutants were used to force heterokaryon formation to determine vegetative compatibility groups (VCGs) and their relation to virulence and geographic origin of (F.O.C.). Twelve distinct VCGs were identified among 25 isolates of (F.O.C.) and the other 27 isolates were incompatible with any of the identified VCGs, reflecting the higher genetic diversity among the isolates of (F.O.C.). There was no definite relationship between VCG groups, virulence and geographic origin among isolates. According to the available literature, these are the first notes on the genetic diversity of F. oxysporum f.sp. cumini, the causal of vascular wilt disease of cumin in Egypt.