1a. Objectives (from AD-416)
1) Develop genetic resources and cropping practices that increase cotton water-use efficiency. 2) Develop new cotton genetic resources with improved fiber quality, lint yield stability, and adaptation. 3) Develop management techniques for cotton grown with conservation tillage after a winter biofuel crop.
1b. Approach (from AD-416)
Basic genomic and applied research will be conducted on improving cotton water use efficiency. In this research, molecular techniques will be used to search for genes that may provide more tolerance to water-deficit stress. Field studies will be conducted to screen cotton germplasm for water-deficit stress tolerance and to determine how agronomic practices affect plant water status. Contemporary plant breeding methods will be used to develop and release high yielding germplasm lines with improved fiber quality. Germplasm combining ability studies as well as studies determining genetic mechanisms for improved fiber quality will be conducted to accelerate the germplasm development program. We will evaluate cotton production potential when double cropped with winter crops harvested for biofuels. Winter crop biomass and energy content, cotton seedling establishment, and cotton fertility needs will be assessed.
3. Progress Report
Cotton water use efficiency research. Two research projects were continued to identify genes in cotton that are involved in plant water use. The first project focused on identifying the aquaporin genes in cotton. Aquaporin gene products are proteins in cell membranes that facilitate water movement in and out of cells. This research has resulted in a recently published manuscript that describes the identification of 71 cotton aquaporin genes and reports that the expression of the genes for some of these aquaporins depends on plant tissue types. The second project focuses on identifying a broad set of genes that show expression patterns sensitive to soil water availability. Thus far, more than 50 water sensitive genes have been identified. We anticipate that both research experiments will provide useful targets for the genetic improvement of water use efficiency in cotton. Besides the gene identification research, water use efficiency field research was conducted. Field trials were conducted on a very low water holding capacity soil evaluating approximately 50 cotton lines for tolerance to drought. In addition, field research was conducted to determine whether the root hydraulic conductance response of cotton to fertilizer nitrogen is genotype specific. Information gained from this research will be used in the development of improved cotton genotypes. Genetic Improvement Research. Two research experiments are currently being conducted with the ultimate goal of developing new cotton genetic resources with improved fiber quality, lint yield stability, and adaptation. The first experiment is evaluating the breeding combining ability of the high fiber quality and genetically diverse Pee Dee germplasm with cotton germplasm developed in numerous other US cotton production areas. Preliminary analysis of year 1 field data identify specific Pee Dee germplasm lines that combine well with other US cotton germplasm to develop breeding offspring with high fiber quality and excellent lint yield potential. The second experiment is determining the genetic relationships between several germplasm sources of high fiber quality. Preliminary analysis of year 1 field data suggests that these germplasm sources likely contain and transmit different genetic factors for high fiber quality that can be combined to further improve fiber quality. We anticipate that both research experiments will provide information and breeding populations to develop new cotton genetic resources with improved fiber quality, lint yield stability, and adaptation. Winter Cover Crop Biomass Feedstock Research. Field studies were continued to determine the potential of using winter cover crops in cotton as sources for biofuel. Plant samples have been collected from these trials and they are currently being analyzed for energy content. Their suitability as a bioenegy feedstock blend with other biomass sources (i.e., animal manures) will be determined.
1. Identified the aquaporin gene family in cotton. Water deficit stress is a major cause of yield and quality reductions in the cotton harvested in the United States and around the globe. Since aquaporin proteins in cell membranes facilitate water movement in and out of cells, genetically improving cotton to better withstand periods of low soil water could be greatly aided by the identification of the genes for these proteins. ARS researchers in Florence, SC, and Stoneville, MS, made a comprehensive identification of 71 cotton aquaporin genes. Sixty-two aquaporin genes were newly discovered. Phylogenetic analysis of amino acid sequences divided the large and highly similar multi-gene family into the known 5 aquaporin subfamilies. This is the first research to discover two of these subfamilies in cotton. Gene expression analysis showed that some aquaporin genes are preferentially expressed in root, leaf, or fiber tissues; whereas other aquaporin genes are equally expressed across these plant tissues. Together with expression and bioinformatic analyses, our results indicate that the genes identified represent an important genetic resource providing potential targets to modify the water use properties of cotton.
2. Documented the status of eight international cotton germplasm collections. Long-term preservation of cotton germplasm provides a genetic insurance policy against unforeseen diseases and pests that threaten future cotton production. Cotton germplasm collections also provide unique genetic materials that can be used to develop new and innovative cotton products. Knowledge of the status and makeup of global cotton germplasm resources provides cotton breeders a great resource to maximize the use of available cotton germplasm. ARS researchers from Florence, SC, Mississippi State, MS, and College Station, TX, collaborated with researchers from Australia, Brazil, China, France, India, Russia, and Uzbekistan to document the status of the global cotton germplasm resources (in 2008). The research highlighted several cotton species that are threatened by extinction if efforts are not made to collect and preserve those species. The research provides cotton researchers a single, all-inclusive resource to determine the extent of the world’s cotton germplasm. Cotton scientists can use this information to expand their use of cotton germplasm to develop the next generation of improved cotton cultivars.
3. Genetically characterized the Pee Dee cotton germplasm resources. After 70 years of cotton breeding activities, the Pee Dee cotton germplasm program has developed a unique and diverse collection of high fiber quality germplasm resources that continue to contribute to the development of current commercial cultivars. Using molecular marker generated genetic fingerprints and field performance data, ARS researchers from Florence, SC, estimated the levels of genetic diversity in the Pee Dee cotton germplasm collection. The research has two important implications for cotton breeders and producers. First, the research shows that substantive and useful genetic diversity remains in the Pee Dee germplasm collection. This means that cotton breeders can continue using Pee Dee germplasm resources to develop new high yielding and high fiber quality cotton cultivars. Second, the research also provides cotton breeders a knowledge-based strategy to select specific breeding cross combinations to use for specific breeding objectives. The research is expected to both improve cotton breeding efficiency and facilitate a broadening of the genetic base in cotton so that long-term genetic improvement can continue.
4. Summer legumes in cotton rotations. Nitrogen fertilizer prices are closely linked to prices of fossil fuels. Finding ways to reduce manufactured nitrogen fertilizer use in cotton could improve sustainability. ARS researchers in Florence, SC, in collaboration with Clemson University, evaluated the potential of using summer legumes, grown the season before cotton, as a nitrogen source for cotton. The two summer legumes evaluated, cowpeas and sunn hemp, accumulate significant amounts of nitrogen, but the research indicated that most of that nitrogen was not available to a subsequent cotton crop. Either it was lost during the winter or bound in the soil organic matter. It appears that a better rotation scheme with summer legumes would be winter crops such as wheat. The findings contribute to the body of knowledge being used to develop new crop production practices that are economically feasible and environment-friendly.Bradow, J.M., Bauer, P.J. 2010. Germination and seedling development. In: Stewart, J.McD. et al., editors. Physiology of Cotton. Heidelbert, Germany: Springer-Verlag GmbH. p. 48-56.