Submitted to: APS Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 5/18/2015
Publication Date: N/A
Technical Abstract: Fusarium wilt of cotton, caused by Fusarium oxysporum f. sp. vasinfectum (Fov), occurs in most cotton growing areas of the world. Pathotypes of Fov have been categorized into eight races based on virulence to different hosts. However, lack of reciprocal resistance reactions among cotton cultivars to putative races has made assignment problematic. We propose to subdivide Fov isolates into vascular competent (VC) and vascular incompetent (VI) pathotypes, based on their ability (VC) or inability (VI) to produce wilt in a standard stem-puncture assay. Isolates of the Australian biotypes, race 4, and race 7 which had identical sequence type with race 4 based on several gene fragments, cause wilt when young cotton roots are dipped in conidial suspensions or when suspensions are injected into the soil around the plant. But these isolates fail to produce wilt when conidia are puncture-inoculated into stem and thus are classified as VI. Race 1, 2, 6 and 8 isolates produce wilt symptoms when the cotton is stem-puncture or root-dip inoculated, but not when conidia are inoculated into soil; thus they are classified as VC. These results correspond with field observations that VI isolates cause wilt without vectoring by nematodes, while VC isolates require co-infection by root knot nematodes to exhibit severe disease. VC isolates produce the heptaketides, nectriafurone, anhydrofusarubin lactol, and 5-O-methyljavanicin. VI isolates consistently produce fusaric acid.