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. lyc opersici, of two physiological races, and eight isolates of other form ae speciales of F. oxysporum were subjected to DNA restricion fragment length polymorphism (RFLP) analysis. Fifty genomic clones from a libr ary produced from an isolate of F. o. f. sp. lycopersici (FRC 0-1078, race 2) were used individually as probes in Southern hybridizations wi th DNA of the 55 isolates digested with four restriction enzymes. From the hybridization pattern observed after a high-stringency wash, it w as estimated that the genome of F. o. f. sp. lycopersici is composed o f 68, 12, and 20% single-copy, multiple-copy, and repetitive DNAs, res pectively. Two clones were identified that were specific to vegetative compatibility group (VCG) 0030, the major VCG of F. o. f. sp. lycoper sici, and another two clones differentiated F. o. f. sp. lycopersici f rom the other formae speciales. RFLP patterns were recorded as phenoty pes, and a dendrogram was constructed based on cluster analysis of sim ilarity coefficients using the unweighted pair-group method with arith metic average. A principal components analysis revealed the relatednes s of each isolate. Results indicate that isolates within each VCG are clonal derivatives of a common ancestor, and that races arose independ ently 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 relia ble indicator of evolutionary origin and population structure of F. ox ysporum.