|Kistler, H - Corby|
Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/7/2003
Publication Date: 8/1/2003
Citation: Gale, L.R., Katan, T., Kistler, H.C. 2003. The probable center of origin of Fusarium oxysporum f. sp. lycopersici VCG 0033. Plant Disease. 87:1433-1438. Interpretive Summary: Fusarium wilt of tomato, caused by Fusarium oxysporum f. sp. lycopersici (FOL) is a major disease in nearly all tomato growing regions worldwide and has been reported in at least 32 countries. Three races of FOL are known to exist, distinguished by their virulence to tomato varieties that contain particular genes for disease resistance. FOL race 3 is a particular problem because few commercial tomato cultivars with race 3 resistance are available. This study demonstrates that since the 1980s, a new type of FOL race 3 has spread in farmers fields in Florida. This new race was not derived from the old race 3 and likely arose in the Tampa Bay area of Florida. Therefore, quarantine efforts in order to exclude or to limit the occurrence of race 3 in Florida ultimately may fail due to the ability of this pathogen to arise from endemic strains of the fungus. This publication therefore would benefit regulatory agencies involved in quarantine efforts as well as other researchers who study how fungi change to over time to become more virulent pathogens. Ultimately this knowledge will aid tomato growers by allowing information-based decisions on the types of tomato varieties they may plant.
Technical Abstract: Isolates of the tomato wilt pathogen Fusarium oxysporum f. sp. lycopersici, predominantly from commercial tomato fields in Florida and southwestern Georgia were characterized using vegetative compatibility grouping (VCG), nuclear RFLPs and virulence. All field isolates that could be grouped into VCG, belonged to VCG 0033. This VCG was first described by Marlatt et al. in 1996 for isolates from northern Florida, Arkansas and North Carolina. This study demonstrates that VCG 0033 is also widespread in central and southern Florida, in addition to southwestern Georgia and also was found to be present in Puerto Rico. Population genetic and phylogenetic analyses of 121 isolates indicated that molecular diversity among VCG 0033 isolates was by far the highest in Manatee County, Florida suggesting it to be the probable center of origin of this relatively newly described VCG. Virulence tests with a subset of isolates, identified all VCG 0033 isolates as race 3, though differences in aggressiveness were observed among tested isolates, independent of resistance genes in the differential cultivars. The widespread VCG 0030 of F. oxysporum f. sp. lycopersici was not present in our field collections. This was unexpected as strains from Florida isolated prior to 1990 were predominantly VCG 0030. This would suggest that VCG 0033 has replaced VCG 0030 in recent years in commercial tomato fields of Florida and southwestern Georgia.