ELECTROPHORETIC KARYOTYPE VARIATION AMONG PATHOTYPES OF FUSARIUM-OXYSPORUM F-SP DIANTHI

Karyotype analysis by pulsed-field gel electrophoresis was applied to characterize isolates of Fusarium oxysporum f.sp. dianthi, the causal agent of Fusarium wilt on carnation. Eleven distinct chromosomal DNA p atterns were detected among 38 pathogenic isolates, and the total geno me size was estimated to range from 23.7 to 36.4 Mb. Except for isolat es belonging to pathotypes 2 and 4, all members of the same pathotype shared overlapping electrophoretic karyotypes. Karyotypes of isolates assigned to pathotypes 1 and 8 showed a high degree of similarity, in accordance with VCG and RFLP analysis. The same electrophoretic karyot ype was also shared by members of pathotypes 2 and 5, thus confirming results obtained by both VCG and RFLP grouping. A single representativ e of pathotype 6, previously confined to the same VCG and RFLP group a s pathotypes 2 and 5, had a slightly different chromosomal pattern. Is olates assigned to pathotype 4 showed four related karyotypes which pa rtially differed in both the number and size of chromosomal bands. How ever, all strains assigned to this pathotype shared a basic profile of nine chromosomal bands, while two low-molecular-weight bands were pre sent or absent. The findings are discussed with regard bath to the sui tability of race distinction in the case of the special form dianthi o f F. oxysporum and to the use of karyotype analysis by PFGE as a tool for the study of the population genetics of this fungus.