Survey of Fusarium Oxysporum F. SP. Vasinfectum Race 4 in Arizona Cotton

Fusarium species are implicated in several diseases of cotton including root rot, the seedling disease complex, and wilt as well as boll rot. A survey was conducted to identify the Fusarium species present in stems, roots and rhizosphere soils of cotton fields in Arizona. Of particular interest is to determine the distribution of F. oxysporum f. sp. vasinfectum (FOV, in particular race 4) across Arizona cotton fields. Two hundred cotton samples were collected from seven counties in AZ and Fusarium isolates were recovered from stem, root, and rhizosphere soils using Komada and PDA medium. A total of 132 isolates of Fusarium species were recovered from stem, roots and soils. The seven Fusarium species recovered included F. brachygibbosum (7%), F. culmorum (3%), F. equiseti (16%), F. fujikuroi (4%), F. oxysporum (20%), F. proliferatum (4%), and F. solani (46%). F. solani was predominant and was more common in the soil (80%) than from cotton roots (20%). The next prevalent Fusarium species was F. oxysporum, occurring more in cotton roots (60%) than in the soil. Approximately 76% of F. oxysporum isolates were identified as FOV using FOV-specific primer pairs Fov1-Eg-f and Fov1-Eg-r. Pathogenicity tests are being conducted to assess whether F. oxysporum isolates are pathogenic with respect to the ability to induce Fusarium wilt in cultivated cotton. The genotypes of FOV isolates are being determined based on sequencing of the translation elongation factor (EF-1α), phosphate permease-like protein (PHO), β-tubulin (tub2), and intergenic spacer regions (ITS). FovT-R primers are being used to determine whether race 4 is present in this collection of FOV isolates. Our survey results will be useful for cotton breeding and selection of suitable cotton cultivars for better control of Fusarium wilt in Arizona.