E. A. Holmes, Department of Plant Pathology, University of California, Davis 95616;
R. S. Bennett and
D. W. Spurgeon, Western Integrated Cropping Systems Research Unit, United States Department of Agriculture--Agricultural Research Service, Shafter, CA 93263;
P. D. Colyer, Louisiana Agricultural Experiment Station, Red River Research Station, Bossier City 71113-8550; and
R. M. Davis, Department of Plant Pathology, University of California, Davis
Sixty-one 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 southeastern United States. Analysis of partial sequences of the translation elongation factor gene revealed four novel genotypes, as well as the presence of races 3 and 8 for the first time in the United States outside of California. The majority of isolates (16 of 27) 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, and β-tubulin genes and their pathogenicity on a total of six Upland (Gossypium hirsutum) and Pima (G. barbadense) cotton cultivars. Two 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 cv. Phytogen 800 was relatively resistant to all genotypes of the pathogen. These results indicate that the population of F. oxysporum f. sp. vasinfectum in the southeastern United States is more diverse than previously recognized.