Population structure of Fusarium oxysporum f. sp. radicis-lycopersici in Florida inferred from vegetative compatibility groups and microsatellites

Fusarium crown and root rot caused by Fusarium oxysporum f. sp. radicis-lycopersici (FORL) is a serious soilborne disease reducing tomato yields in Florida, a leading state in fresh market tomato production in the United States. One hundred and twenty five isolates of FORL were collected from the three main tomato-growing counties in Florida between 2006 and 2008. Vegetative compatibility groups (VCGs) and 10 microsatellite loci were used to infer the population structure of FORL. Up to 69.8 % of the isolates could be assigned to one of three VCGs, 0094, 0098 or 0099, with frequencies of 38.6, 24.4, and 6.8 % respectively. A medium level of population differentiation (Φst = 0.159) was detected among the three counties, and three optimal clusters (populations) were supported by discriminant analysis of principal components. In addition, each population had some individuals that likely migrated from other populations. Migration probably played an important role in shaping the population structure of FORL since repeated VCGs and multilocus genotypes were observed in the three counties. Considerable migrants (> 1.33 migrants per generation) were also detected between the three counties, resulting in an increase in the effective population size and genetic diversity of F. oxysporum f. sp. radicis-lycopersici. Although migration is an important evolutionary force, mutation and parasexual recombination could not be completely ruled out as contributing causes to the genetic diversity of FORL. Management strategies that limit the movement of F. oxysporum f. sp. radicis-lycopersici are necessary to reduce the evolutionary potential of the pathogen.