Submitted to: Journal of Cotton Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 12, 2013
Publication Date: N/A
Interpretive Summary: Fusarium wilt of cotton is a disease caused by a soilborne fungus, Fusarium oxysporum f. sp. vasinfectum. This fungus exists as several strains that vary in ability to attack cotton cultivars and other crops, and these strains are generally categorized as races. Strains of Fusarium can be distinguished chemically based on specific DNA sequences (molecular markers). Fusarium isolates similar to a race 4, a strain that is particularly damaging in California, were recently reported in Alabama and Mississippi. This study compared four of the race 4-like strains to reference strains of race 4 using molecular markers. The molecular markers showed the isolates from Alabama and Mississippi are different from the reference isolates of race 4. These results indicate that race 4 has not yet been found in the southeastern cotton belt.
The presence of race 4-like isolates of Fusarium oxysporum f. sp. vasinfectum from the southeastern U.S. was recently reported. Race 4 can cause significant damage to Upland cultivars in the absence of root-knot nematodes; therefore, the discovery of this race in the Southeast could have serious implications. Four of the race 4-like isolates, collected in 2009-2010 from Auburn University's E. V. Smith Research Center in Alabama and Mississippi State University's R. R. Foil Research Center, were examined further using sequences of the nuclear ribosomal DNA intergenic spacer region (IGS rDNA) in addition to the translation elongation factor (EF-1a). The four southeastern isolates were identical to reference isolates of race 4 in EF-1a sequence, but differed from each other and from reference isolates of race 4 in IGS sequence. These results show that race identification cannot be based solely on EF-1a sequence data, and that the race 4-like isolates from Alabama and Mississippi are distinct from race 4. Therefore, race 4 of F. oxysporum f. sp. vasinfectum has not yet been found in the southeastern U.S.