ABSTRACT

Because there is concern over the introduction of highly virulent Australian strains of Fusarium oxysporum f. sp. vasinfectum (FOV) into California, it is necessary to characterize local strains of the fungus to document the movement of genotypes in and out of important cotton-producing areas. Regulatory decisions may rely on such data regarding movement of plant material between states or countries where different strains exist. To accurately describe the strains that presently occur in California, various genetic methods were employed. Based on partial sequences of translation elongation factor and beta-tubulin genes and restriction enzyme digestion of the IGS nuclear r-DNA, Australian isolates of FOV do not exist in California. Californian isolates fell into four lineages. One group of several isolates consisted of the lineage of races 1 and 2, which are closely related to each other; a second group was represented by two isolates that may or may not belong to the race 3 lineage; a third group, race 4, was commonly collected in California; and a fourth group, race 8, was represented by two isolates. Race 4 was highly virulent on Pima in greenhouse pathogenicity tests and was considerably less virulent on Acala; isolates belonging to the lineage of races 1, 2, and 6 were relatively virulent on Acala cotton but not Pima. Race 8 and race 3(?) were weakly pathogenic on both Acala (Maxxa and Phy-72) and Pima (DP-744 and Pima S-7).