| A total of 155 isolates of Fusarium oxysporum f. sp. vasinfectum were collected from cotton plants (Gossypium spp.) with symptoms of Fusarium wilt to determine the composition of races present in the United States. Phylogenetic analysis of partial sequences of the translation elongation factor gene revealed five novel genotypes, as well as the presence of races 3 and 8 for the first time in the U.S. outside of California Many isolates (17 of 40) sampled from Arkansas were novel genotypes. A subset of isolates, representing the novel genotypes was compared with previously described races using sequences from translation elongation factor, phosphate permase, beta-tubulin, and mitochondrial small subunit genes, restriction fragment length polymorphisms in the intergenic spacer region, vegetative compatibility groupings, and pathogenicity on a total of six Upland ( G. hirsutum L.) and Pima (G. barbadense L.) cotton cultivars. Three of the novel genotypes belonged to a clade containing races 1, 2, 4, 6, and 8 and two shared ancestry with race 3. All new genotypes were pathogenic to at least some of the cotton cultivars tested. The Pima cultivar Phytogen 800 was relatively resistant to all genotypes of the pathogen. These results indicate that the population of F. oxysporum f. sp. vasinfectum throughout the U.S. is more diverse than previously recognized. Furthermore, vegetative compatibility grouping revealed that race 4 isolates collected from throughout California are of a single origin. |
