Population Genetic Analysis Corroborates Dispersal of Fusarium oxysporum f. sp. radicis-lycopersici from Florida to Europe

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Abstract
Fusarium oxysporum isolates from tomato plants displaying crown and root rot symptoms were collected in central and southern Florida and analyzed using vegetative compatibility grouping (VCG) and nuclear restriction fragment length polymorphism (RFLP) data. VCG 0094 of F. oxysporum f. sp. radicis-lycopersici, previously known only from northwestern Europe, was predominant among 387 isolates assessed. In addition, two newly described VCGs (0098 and 0099) were detected at low frequencies. Floridian VCG 0094 isolates displayed a continuum of compatibilities, which is in contrast to the three distinct subgroups previously identified among European VCG 0094 isolates. RFLP haplotypes were constructed using one repetitive and three low-copy probes. Population subdivision of VCG 0094 from various Floridian counties and from northwestern Europe (Belgium, the Netherlands, and the United Kingdom) was evaluated by analysis of molecular variance. A “natural” population structure was revealed, differentiating populations from the east and west coasts of Florida. In addition, isolates from Europe were statistically indistinguishable from the Palm Beach County, FL, population. Furthermore, gene diversity among Palm Beach County VCG 0094 isolates was more than five times greater than among European isolates. Results from both VCG and RFLP analyses strongly support the inference that the European VCG 0094 constitutes a founder population that resulted from intercontinental migration of a few isolates from Palm Beach County, FL.