2012 US Survey of Fusarium oxysporum f. Sp. Vasinfectum Distribution

Fusarium wilt, caused by Fusarium oxysporum f. sp. vasinfectum, is a major disease of cotton found throughout the cotton belt of the United States. Although the distribution of races 1, 2, 3 and 8 has been documented, industry and academic partners are interested in assessing the distribution of race 4, a highly virulent strain widespread in California. Samples of diseased cotton plants were submitted for race identification to the Davis Lab from growers' fields in California, Texas, Missouri, Mississippi, South Carolina, Alabama, Arkansas and Louisiana. Fungal DNA was isolated and PCR reactions were run with both race 4 specific primers and primers specific to the elongation factor sequence (EF1 and EF2). DNA samples that failed to produce an amplicon with race 4 specific primers were then amplified with the EF primers and sequenced. Sequences were then compared to our own database and the NCBI database. After the sequences were aligned with ClustalX and manually edited, a phylogenetic tree consisting of all known genotypes of FOV was constructed by maximum parsimony analysis using PAUP. The analysis of the new isolates confirmed relationships previously published by Davis et al in 2005, with distinct lineages for races 1, 2, 4 and 8 as well as the race 3 cluster. Several new genotypes in the race 3 lineage and one unique isolate in the race 8 lineage were identified. Two isolates with the same EF sequence as CA 14 (FOV-4) were identified from Mississippi. Those samples, however, did not produce an amplicon with race 4 specific primers and were, therefore, considered unique genotypes. Pathogenicity tests have not yet been conducted. More than 90 isolates collected in California in 2012 were identified as race 4; to the best of our knowledge, FOV-4 remains limited to California.