Seventy seven monoconidial isolates of A. flavus were recovered from pistachio seed and pistachio processing residues at different areas of Kerman province. Nitrate non-utilizing mutants (nit) were isolated on Czapek Dox Agar amended with KClO3 for 48 isolates, with other isolates producing no nit mutants. Phenotype of nit mutants was determined on Czapek amended with various nitrogen sources (nitrate, nitrite, amonium, uric acid and hypoxantine), so that 75% of mutants were found to be nit1, 18% nit3 and 7% nitM. Complementation between nit mutants was tested on Czapek Dox Agar. Twenty one isolates were assigned to four vegetative compatibility groups (VCGs) based on formation of heterocaryon, designated as Af1, Af2, Af3 and Af4, while 27 isolates produced no heterocaryon and did not categorize into any VCG. Sclerotium production ability was analyzed for all isolates in which only 16.6% of isolates were found to produce sclerotium. There was no relationship observed between vegetative compatibility groups (VCGs), sclerotium production ability and geographic distribution. This study revealed that population of the fungus did not show any high level of diversity in Kerman province even though isolates can exchange genetic materials through hyphal anastomosis and formation of heterocaryon
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