Characterization of Fusarium Oxysporum Genotypes Causing Wilt in Georgia Cotton

Since 2011 severe outbreaks of Fusarium wilt of cotton in Georgia have raised concerns about the genotypes of the causal pathogen, Fusarium oxysporum forma speciales vasinfectum. We recovered 492 F. oxysporum isolates from 107 wilted plants collected from 7 fields in 5 counties, and determined their relatedness utilizing vegetative complementation (VC) tests and DNA sequence analysis. Eight VCGs, VCG0111 (race 1), VCG0112 (race 2), VCG01117B, VCG01117C, VCG01118, VCG01119 (race 8), VCG01120 and VCG01121, were found and their phylogenic relationships determined. VCG01121 has never before been reported but was the most commonly isolated VCG in this collection. This VCG was especially prominent in Berrien County, the center of the outbreaks. Two pathogenicity tests that can distinguish vascular competent isolates from root-rot pathotype isolates were used to characterize the 8 VCGs. All 8 VCGs were the vascular competent pathotype and in our assays required root-knot nematode (Meloidogyne incognita) to cause wilt. Therefore, use of nematode resistance cultivars seems a viable approach to control this disease in Georgia when appropriate. Management of plant-parasitic nematode to reduce impact of Fusarium wilt can also be accomplished through use of nematicides.