POPULATION-STRUCTURE OF FUSARIUM-OXYSPORUM F SP LYCOPERSICI - RESTRICTION-FRAGMENT-LENGTH-POLYMORPHISMS PROVIDE GENETIC-EVIDENCE THAT VEGETATIVE COMPATIBILITY GROUP IS AN INDICATOR OF EVOLUTIONARY ORIGIN

A worldwide collection of 47 isolates of Fusarium oxysporum f. sp. lycopersici, of two physiological races, and eight isolates of other formae speciales of F. oxysporum were subjected to DNA restricion fragment length polymorphism (RFLP) analysis. Fifty genomic clones from a library produced from an isolate of F. o. f. sp. lycopersici (FRC 0-1078, race 2) were used individually as probes in Southern hybridizations with DNA of the 55 isolates digested with four restriction enzymes. From the hybridization pattern observed after a high-stringency wash, it was estimated that the genome of F. o. f. sp. lycopersici is composed of 68, 12, and 20% single-copy, multiple-copy, and repetitive DNAs, respectively. Two clones were identified that were specific to vegetative compatibility group (VCG) 0030, the major VCG of F. o. f. sp. lycopersici, and another two clones differentiated F. o. f. sp. lycopersici from the other formae speciales. RFLP patterns were recorded as phenotypes, and a dendrogram was constructed based on cluster analysis of similarity coefficients using the unweighted pair-group method with arithmetic average. A principal components analysis revealed the relatedness of each isolate. Results indicate that isolates within each VCG are clonal derivatives of a common ancestor, and that races arose independently within each VCG. In addition, there is evidence to suggest that mutations have occurred in vegetative incompatibility loci, resulting in many single-member VCG isolates (VCG 003-) that cluster with VCGs. RFLP analysis of total genomic DNA reveals that the VCG can be a reliable indicator of evolutionary origin and population structure of F. oxysporum.