Two genetically distinct populations of Fusarium oxysporum f sp lycopersici race 3 in the United States

Isolates of Fusarium oxysporum f. sp. lycopersici from the United States, Australia, and Mexico were examined for vegetative compatibility, pathogenicity on a set of differential tomato cultivars, mitochondrial DNA (mtDNA) restriction fragment length polymorphisms (RFLPs), and isozyme polymorphisms. The collection of 113 isolates included representative isolates of races 1, 2, and 3, and the three previously described vegetative compatibility groups (VCGs). A new and previously undescribed VCG, VCG 0033, was identified that contained race 3 isolates of F. oxysporum f. sp. lycopersici from locations in Arkansas, North Carolina, and Florida. Previously described race 3 isolates belonged to VCG 0030. Recently recovered race 3 isolates from Mexico also belonged to VCG 0030. VCGs 0030 and 0033, which both contain race 3 isolates, represent genetically distinct populations based on vegetative compatibility, mtDNA RFLPs, and isozyme differences. These data support the hypothesis that isolates of F. oxysporum pathogenic on tomato may represent two genetically distinct evolutionary lineages. No differences in pathogenicity or virulence (aggressiveness) were detected among race 3 isolates from each of the two VCGs in greenhouse inoculation tests.