MOLECULAR CHARACTERIZATION OF RACES AND VEGETATIVE COMPATIBILITY GROUPS IN FUSARIUM-OXYSPORUM F SP VASINFECTUM

Restriction fragment length polymorphism (RFLP) and vegetative compati bility analyses were undertaken to assess genetic relationships among 52 isolates of Fusarium oxysporum f. sp. vasinfectum of worldwide orig in and representing race A, 3, or 4 on cotton plants. Ten distinct veg etative compatibility groups (VCGs) were obtained, and isolates belong ing to distinct races were never in the same VCG. Race A isolates were separated into eight VCGs, whereas isolates of race 3 were classified into a single VCG (0113), as were those of race 4 (0114). Ribosomal a nd mitochondrial DNA (rDNA and mtDNA) RFLPs separated four rDNA haplot ypes and seven mtDNA haplotypes. Race A isolates displayed the most po lymorphism, with three rDNA haplotypes and four mtDNA haplotypes; race 4 isolates formed a single rDNA group but exhibited three mtDNA haplo types, while race 3 isolates had unique rDNA and mtDNA haplotypes. Two mtDNA molecules with distinct sizes were identified; the first (45-kb mtDNA) was found in all race A isolates and seven race 4 isolates, an d the second (55-kb mtDNA) was found in all race 3 isolates and in two isolates of race 4. These two mtDNA molecules were closely related to mtDNAs off. oxysporum isolates belonging to other formae speciales (c onglutinans, lycopersici, matthioli, and raphani). Isolates within a V CG shared the same rDNA and mtDNA haplotypes with the exception of VCG 0114, in which three distinct mtDNA haplotypes were observed. Genetic relationships among isolates inferred from rDNA or mtDNA site restrict ion data were different, and there was not a strict correlation betwee n race and RFLPs. However, the races in F. oxysporum f. sp. vasinfectu m constituted three distinct genetic groups with regard to VCG and nuc lear and mtDNA RFLPs.