Variation in mitochondrial DNA among vegetatively compatible isolates of Fusarium oxysporum

Abstract

Thirty-nine isolates of Fusarium oxysporum, obtained from agricultural field soils in California, were examined for variability in mitochondrial DNA. Thirteen isolates belonging to the same vegetative compatibility group all had the same mitochondrial DNA haplotype (C). Among 11 isolates in a second vegetative compatibility group, there were two mitochondrial DNA haplotypes, A (8 isolates) and B (3 isolates). At least three changes in length appear to be necessary to inter-convert mitochondrial DNA haplotypes A and B. To assess the potential for exchange of mitochondrial DNA haplotypes between isolates in different vegetative compatibility groups, we examined 15 isolates of F. oxysporum which collectively represented 11 pairs of weakly compatible isolates in otherwise distinct vegetative compatibility groups. In 8 of these 11 pairs the 2 isolates had different mitochondrial DNA haplotypes, either A or B; in the remaining 4 pairs both isolates had the same mitochondrial DNA haplotype. Our data indicate that weak vegetative interactions may permit transfer of mitochondria between isolates in different vegetative compatibility groups.