Statement of Problem: Fusarium oxysporum f.sp.Vasinfectum (FOV) is a widely spread soil-borne fungus that attacks cotton and other plants. FOV causes a general wilt. Its symptoms include leaf yellowing and necrosis beginning at the leaf margins. The vascular system of infected plants becomes “plugged up” from the fungus and the plant’s defense response to the infection. Previously identified FOV races infect plants through injuries caused by root knot nematodes. Root knot nematodes are most widely found in coarse texture soils in the San Joaquin Valley. Crop rotation or chemical applications reduce nematode populations so their damage is not significant. However, a new race of FOV, Race 4, has been identified in California. Race 4 is different because it can infect cotton plants in the absence of nematodes, causing infections in both coarse and fine textured soils. Generally, Pima cotton varieties are more susceptible than Acala or other upland varieties are to FOV Race 4.
UC ANR FOV Race 4 Research: Researchers from the University of California and USDA Agriculture Research Service housed at the UC Shafter Research and Extension Center and UC Davis Plant Pathology Department have attacked the problem in three ways. We have developed methods for early identification. We have further described the FOV life cycle and identified methods and plant parts that could potentially spread the organism. To reduce or prevent FOV spread within and between fields, we have developed best management practices, including phytosanitary procedures. Other research has been conducted on cotton plant resistance. We have evaluated hundreds of varieties and breeding lines in the Kearney greenhouse for resistance to FOV Race 4. Field evaluations have been conducted on the most promising varieties to further verify resistance. We are categorizing the genes that convey resistance and identify molecular markers for those genes.
New Pima varieties resist FOV Race 4: San Joaquin Valley growers have shifted to plant more high quality Pima cotton, which commands a premium price. Our identification of resistant Pima varieties has enabled the continued success of the industry. Based upon our research findings, California cotton growers are able to continue growing resistant Pima cotton varieties in areas where FOV Race 4 is present. Planting resistant cotton varieties is one of the best management practices to reduce the spread of FOV.