Progress report on a contemporary survey of the Fusarium wilt fungus in the United States

Authors: Bennett, Rebecca; Bell, Alois - Al; WOODWARD, JASON - Texas A&M University; LAWRENCE, KATHRYN - Auburn University; ROTHROCK, CRAIG - University Of Arkansas; KIRKPATRICK, TERRY - University Of Arkansas; LAWRENCE, GARY - Mississippi State University; COLYER, PATRICK - Louisiana State University; DAVIS, R. MICHAEL - University Of California

Submitted to: National Cotton Council Beltwide Cotton Conference
Publication Type: Proceedings
Publication Acceptance Date: 1/18/2011
Publication Date: 4/25/2011
Citation: Bennett, R., Bell, A.A., Woodward, J.E., Lawrence, K.S., Rothrock, C.S., Kirkpatrick, T.L., Lawrence, G.W., Colyer, P., Davis, R. 2011. Progress report on a contemporary survey of the Fusarium wilt fungus in the United States. National Cotton Council National Cotton Council of America, Memphis, TN. Beltwide Cotton Conference, Altanta, Georgia, January 4 to 7, 2011. pp. 267-274.

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. These strains are generally categorized as races or lineages, although some appear distinct from races that have so far been identified. Planting disease-resistant cultivars is an important tactic for managing Fusarium wilt of cotton, but resistance to one Fusarium race or lineage does not confer resistance to others. Therefore, knowledge of the types of races present in cotton production areas of the U.S. is important. Thirty-nine samples of the Fusarium wilt fungus collected from infected cotton plants in the U.S. were compared to known reference strains. Samples from southeastern states were related to four reference strains. In addition, six samples matched reference strains that have not been fully characterized. Some samples from Alabama and Mississippi were similar to a strain (race 4) that is particularly damaging in California. To date, race 4 has not been reported as causing serious disease problems in the Southeast. All samples from Texas were related to known strains that were previously documented. These preliminary results document the potential for increased problems with Fusarium wilt in the Southeast. These findings alert cotton breeders to potential disease problems that may warrant expanded breeding efforts for Fusarium wilt resistance.

Technical Abstract: Knowledge of the genetic and pathogenic diversity present in a pathogen population is required to effectively deploy resistant cultivars. The only pathogenic survey of Fusarium oxysporum f. sp. vasinfectum in the U.S. was conducted in 1983. Since then, new distributions of races 3, 4, and 8, and four novel genotypes of this fungus, have been discovered in the U.S. A multi-state collaboration was initiated with the objective of conducting a comprehensive contemporary survey of the genotypic and pathogenic diversity of F. oxysporum f. sp. vasinfectum in the United States. Preliminary data are presented. A 618-bp fragment of the translation elongation factor gene (EF-1a) was sequenced from 39 isolates collected from eight states. These sequences were compared to those obtained from six isolates from the Ivory Coast and 70 sequences from GenBank. Maximum parsimony analysis yielded six shortest trees with topologies consistent with previous reports. Three isolates from Alabama and two isolates from Mississippi were in Lineage IV (race 4). Other isolates from southeastern states were in Lineages II (race 1) and III (race 8), a clade with genotypes 127 and 140, and an unresolved group related to genotypes 108 and 110. All isolates from Texas and most isolates from the Ivory Coast were in Lineage II. None of the isolates sequenced was in Lineages I (race 3) or V (Australian genotypes). These results support previous reports suggesting F. oxysporum f. sp. vasinfectum in the southeastern U.S. have a high level of genotypic diversity.