|Bell, Alois - Al|
|Ortiz, Carlos - Texas A&M University|
|Stipanovic, Robert - Bob|
Submitted to: National Cotton Council Beltwide Cotton Conference
Publication Type: Proceedings
Publication Acceptance Date: 12/28/2015
Publication Date: N/A
Interpretive Summary: Isolates of the fungus Fusarium oxysporum that cause wilt of cotton were collected from various countries and states in the U.S. to determine genetic relationships among strains. Isolates were subjected to vegetative complementation tests and DNA sequences were determined for several genes. The results show that severe Fusarium wilt in California is due to isolates of a unique genotype (VCG 4; race 4) reported from China in 1985. A less virulent form of VCG 4 was first found in India more than fifty years ago. VCG 4 is now spread throughout Asia. Prior to its recent appearance in California, VCG 4 was not known in the western hemisphere. VCG 4 was not found in any state other than California.
Technical Abstract: From 1992 to 2015 nearly 3,000 isolates of Fusarium species from wilted cotton plants, seed, or cotton field soils were tested for pathogenesis using root-dip, stem-puncture, and soil-infestation assays. The greatest numbers of pathogens were identified by the root-dip assay. These were divided into vascular competent or root rot pathotypes using stem-puncture and soil-infestation assays, respectively. Populations within each pathotype were identified using vegetative compatibility tests and DNA sequencing. The vascular competent pathogens included more than 20 vegetative compatibility groups (VCGs). Isolates named races 1, 2, 6, and 8 occurred in VCG 0111, 0112, 0116, and CPRU 2, respectively. The root rot pathotypes race 3, race 4, and the Australian biotype occurred in VCGs 0113, 0114, and 01111, respectively. VCGs were tested for virulence to Gossypium hirsutum (seven cultivars), Gossypium barbadense ‘Seabrook Sea Island 12B-2’, Gossypium arboreum USDA Acc. No. A1-17, Abelmoschus elegans ‘Clemson Spineless’, Medicago sativa ‘Grimm’, Nicotiana tabacum ‘Dixie Bright’ and ‘Gold Dollar’, Glycine max ‘Yelredo’, Cucumis melo var. cantalupensis ‘Magnum 45’, and Lycopersicon esculentum ‘Bonny Best’. All vascular competent VCGs had host ranges, and virulence to Gossypium species and cultivars, similar to those of the race 1 isolate ATCC 16421. VCGs of the root rot pathoype were specific to Gossypium species and were more virulent to several G. barbadense cultivars than race 1 isolates. Recent increases in severity of Fusarium wilt in California and Georgia were correlated with the appearance and spread of highly virulent strains of VCG 0114 and VCG CPRU 12, respectively.