1a. Objectives (from AD-416)
The objectives of this research are to evaluate and validate improvements within ARS in-house breeding lines in yield and fiber quality traits through comparative field evaluations, and to evaluate and identify sources of Fusarium wilt (FOV) resistance in a diverse cotton germplasm collection, including commercial and experimental cultivars and mapping populations, through field and greenhouse trials.
1b. Approach (from AD-416)
Acala, non-Acala Upland, Pima, and other Gossypium cultivars and germplasm from a broad genetic background will be evaluated for yield and fiber quality properties at both Shafter and West Side Research and Extension Centers of the University of California, and in commercial fields when available. In addition, for Fusarium wilt resistance (FOV), cotton entries will be evaluated at the University of California Kearney Research and Extension Center greenhouses, and in verified FOV race 4 or race 1 infested commercial fields when available. Completely randomized or randomized complete block designs with three or four replications will be used for most trials. A minimum of two replications will be used for yield or FOV resistance estimation when seed availability or study acreage is limited. Plot size in field studies will vary depending on objectives and seed and land availability. In studies focused on yield characters, data collected will include in- and end-of-season measurements of plant height, number and type of nodes, and boll position, retention, and numbers per plant. Fifty-boll and six-pound samples of seed cotton will be collected to estimate lint percentage and fiber quality properties. These cotton samples will be ginned at Shafter to determine lint percent. Where fiber quality is of key interest samples will be sent for analysis to one or more commercial classing laboratories or to the USDA Classing office in Visalia, CA. Studies focused on identification of FOV resistance will assess a diverse cotton germplasm collection, which includes diploid cottons, public germplasm, and germplasm developed by conventional breeding techniques. Measured responses specific to FOV studies will include stand survival rates, ratings of disease severity, and vascular staining. Results of FOV field trials will be supplemented by replicated studies under greenhouse conditions, which will document responses of cultivars or breeding lines to artificially-inoculated soil mixes. Several races of FOV (e.g., races 1 and 4) may be used in greenhouse evaluations to better understand variations in exhibited germplasm resistance responses. In addition, we will evaluate selected control practices such as seed treatment, planting date, and irrigation regimen under different soil types for management of the FOV disease in combination with resistant or tolerant cultivars.
3. Progress Report
The agreement was established in support of objectives 1c and 3 of the approved in-house project, the goal being to evaluate and validate yield, fiber quality, and disease resistance improvements of ARS in-house breeding lines through comparative field and greenhouse evaluations. Continuous improvement of yield, fiber quality, and disease resistance of cotton breeding lines is important to maintain the competitiveness of U.S. cotton. More than 2000 plants were assayed for resistance to races 1 and 4 of the causal organism of Fusarium wilt (Fusarium oxysporum f. sp. vasinfectum) in greenhouse and field studies. Observed disease responses revealed interactions between individual cotton entries and race of Fusarium. Analyses to investigate the inheritance of Fusarium wilt resistance and to identify associated genes were initiated. Ten Pima breeding lines with resistance to Fusarium wilt were evaluated for yield potential and fiber quality at two field locations representing different soil types. Upon release, these breeding lines will expand the genetic base available to cotton breeders for development of Fusarium resistant cultivars. Activities during this project were documented through presentations at meetings of cotton growers, professional societies, and commodity groups, and through telephone contacts and site visits with collaborators.