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A Near-Isogenic Fusarium oxysporum f. sp. lycopersici Strain with a Novel Combination of Avirulence Characteristics

A novel Fusarium oxysporum f. sp. lycopersici strain (F1-27) was obtained from protoplast fusions between race 1 Fol004 (putative avirulence genotype A1a2a3) and race 2 Fol007 (a1A2A3). Bioassays using different tomato cultivars revealed new virulence characteristics for F1-27 that were mitotically stable. The corresponding avirulence genotype for F1-27 was assigned a1A2a3. Despite their distinction in avirulence genotype, molecular analysis revealed that parent Fol007 and F1-27 were near-isogenic strains. The electrophoretic karyotype of F1-27 was identical to that observed for Fol007. Foxy-amplified fragment length polymorphism (AFLP) marker analysis showed that all Fol007-specific bands were present in F1-27. In addition, 11 new F1-27-specific Foxy insertions were identified. Segregation of both virulence and these new Foxy-AFLP markers was observed in a backcross between F1-27 and its parent Fol007. One marker was found to cosegregate with the a3 allele. The nature of the genetic change in this strain is discussed.