2 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 Stat es, 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 is ozyme polymorphisms. The collection of 113 isolates included represent ative isolates of races 1, 2, and 3, and the three previously describe d vegetative compatibility groups (VCGs). A new and previously undescr ibed VCG, VCG 0033, was identified that contained race 3 isolates of F . oxysporum f. sp. lycopersici from locations in Arkansas, North Carol ina, 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, rep resent genetically distinct populations based on vegetative compatibil ity, mtDNA RFLPs, and isozyme differences. These data support the hypo thesis that isolates of F. oxysporum pathogenic on tomato may represen t two genetically distinct evolutionary lineages. No differences in pa thogenicity or virulence (aggressiveness) were detected among race 3 i solates from each of the two VCGs in greenhouse inoculation tests.