Three nuclear type segeragants were isolated from a heterokaryon of Fusarium oxysporum f.sp.vasinfectum strain Ag149.Their cultural character and pathogenicity were different.The differences of their GC content for total DNA and nuclear DNA were between 0 1% to 0 4% and 0 4% to 0 8% respectively,as measured by thermal denaturation method.The 18S rDNA partial sequences of 1477 base pairs in these segregants were identical.