|Campbell, Benjamin - Todd|
Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/13/2013
Publication Date: 11/5/2013
Citation: Hutmacher, R.B., Ulloa, M., Wright, S.D., Campbell, B.T., Percy, R.G., Wallace, T., Myers, G., Bourland, F., Weaver, D., Chee, P., Thaxton, P., Zhang, J., Smith, W., Dever, J., Kuraprthy, V., Bowman, D., Jones, D., Burke, J.J. 2013. Elite-upland cotton germplasm-pool assessment of fusarium wilt (FOV) resistance in California. Agronomy Journal. 105:1635-1644. Interpretive Summary: Integrating disease resistance, into high-yielding, high-fiber quality cultivars continues to be one of primary objectives of many breeding programs. Fusarium wilt is an important disease that reduces yield in cotton. This disease is caused by a fungus that can survive for long periods in the soil, making it impossible to eliminate. In this study, we assessed the vulnerability of elite Upland cotton lines from 13 U.S. public breeding programs across the Cotton Belt to Fusarium wilt disease caused by races 1 and 4 of this fungus. Ten independent replicated field evaluations on three different sites were conducted for this study. Studies of Upland cotton lines revealed interactions in Fusarium wilt disease response between assayed elite lines, Fusarium races (1 and 4), and evaluation sites. Selected elite lines from programs in the states of AL, AR, LA, and MS showed at least a moderate level of tolerance to both Fusarium races. Results from our studies identified genetic sources of Fusarium wilt resistance that could be useful to breeders for cotton improvement. However, elite lines in the current breeders’ public elite-Upland germplasm pool may be more susceptible than expected to Fusarium infection, and sources of resistance may be limited in fields highly-infested with this fungus. Continued development of cotton germplasm with wide adaptability and improved host-plant resistance with enhanced fiber quality is essential for the long-term survival of the U.S. cotton industry.
Technical Abstract: Host-plant resistance is currently the most economic and effective strategy for managing Fusarium wilt [Fusarium oxysporum f. sp. vasinfectum (FOV)] disease. Over the past nine years, a new race of Fusarium (FOV race 4) has increasingly impacted cotton (Gossypium spp.) in production fields in the San Joaquin Valley of California. To assess the vulnerability of Upland cotton (G. hirsutum L.) in California to FOV disease, elite Upland germplasm lines from 13 US public breeding programs across the Cotton Belt and commercial cultivars were evaluated for disease resistance to FOV races 1 and 4. Ten independent replicated field evaluations were conducted for this analysis: three in 2008, four in 2010, and three in 2011, with yield and fiber quality evaluations included at two of these locations in 2010 and one in 2011. FOV evaluations for each test used a randomized complete block or incomplete block design with three replications. Disease severity index (DSI) of leaves, vascular root staining (VRS), and percentage of plant survival (PS) were examined for each plot. Significant differences (P < 0.05) were observed for PS, DSI, and VRS values on the elite germplasm lines in all three years for the levels of resistance-response to FOV races 1 and 4. VRS and PS values were negatively correlated, ranging from r = -0.17 to r = -0.68 within each race and evaluation site, indicating that a high VRS value resulted in low PS. PS averages of the elite germplasm for FOV race 1 were 84 percent (2008), 87 percent (2010) and 47 percent (2011), while PS averages for FOV race 4 were 58 percent (2008), 92 percent (2010) and 81 percent (2011). Significant interactions among germplasm lines, FOV races (1 and 4), and evaluation sites, indicated that germplasm lines differed in mechanisms of plant-defense response for the two FOV races. Selected lines from programs in the states of AL, AR, LA, and MS showed at least a moderate level of tolerance to both FOV races. However, several of these lines produced weak and coarse fibers. Growth and competitiveness of the cotton industry depends upon continual improvements in performance, not only in yield and fiber quality, but disease resistance. Based on these evaluations to date, many of the entries in the current breeders’ public elite-Upland germplasm pool may be more susceptible than expected to some FOV races, and sources of acceptable levels of resistance may be limited when tested under infestation levels that resulted in only 5 to 35 percent plant survival in susceptible check cultivars.