Evolutionary Relationships among the Fusarium oxysporum f. sp. cubense Vegetative Compatibility Groups

ABSTRACTFusarium oxysporumf. sp.cubense, the causal agent of fusarium wilt of banana (Musaspp.), is one of the most destructive strains of the vascular wilt fungusF. oxysporum. Genetic relatedness among and within vegetative compatibility groups (VCGs) ofF. oxysporumf. sp.cubensewas studied by sequencing two nuclear and two mitochondrial DNA regions in a collection of 70F. oxysporumisolates that include representatives of 20 VCGs ofF. oxysporumf. sp.cubense, other formae speciales, and nonpathogens. To determine the ability ofF. oxysporumf. sp.cubenseto sexually recombine, crosses were made between isolates of opposite mating types. Phylogenetic analysis separated theF. oxysporumisolates into two clades and eight lineages. Phylogenetic relationships betweenF. oxysporumf. sp.cubenseand other formae speciales ofF. oxysporumand the relationships among VCGs and races ofF. oxysporumf. sp.cubenseclearly showed thatF. oxysporumf. sp.cubense's ability to cause disease on banana has emerged multiple times, independently, and that the ability to cause disease to a specific banana cultivar is also a polyphyletic trait. These analyses further suggest that both coevolution with the host and horizontal gene transfer may have played important roles in the evolutionary history of the pathogen. All examined isolates harbored one of the two mating-type idiomorphs, but never both, which suggests a heterothallic mating system should sexual reproduction occur. Although, no sexual structures were observed, some lineages ofF. oxysporumf. sp.cubenseharboredMAT-1andMAT-2isolates, suggesting a potential that these lineages have a sexual origin that might be more recent than initially anticipated.