OBJECTIVE 1: Discover and characterize superior traits from natural collections and a mutant population to enhance abiotic stress tolerance, yield potential, and stability of grain, forage, and bioenergy sorghum. Subobjective 1A: Identify new sources of thermal tolerance within diverse Ethiopian germplasm. Subobjective 1B: Identify and characterize genetic variation for root traits contributing to improved thermal tolerance. Subobjective 1C: Screen bioenergy sorghum accessions for high water use efficiency. Subobjective 1D: Characterize independent msd mutants optimized for sorghum grain yield improvement. Subobjective 1E: Isolate sorghum architecture mutants and genes to enhance hybrid vigor. OBJECTIVE 2: Develop new sorghum lines with superior early season cold and drought tolerance, and improved hybrid yield. Subobjective 2A: Develop superior sorghum inbred lines through marker-assisted trait pyramiding. Subobjective 2B: Introgression of Ethiopian photoperiod sensitive germplasm with a U.S. adapted breeding line.
The Southern United States has large regions of crop production where temperatures can be extreme and rainfall is limited. Sorghum can be produced in these areas where corn falters because of sorghum’s high water use efficiency, as well as its superior tolerance to drought and high temperature stresses. Therefore, sorghum is poised to play a major role in crop production under stressful and more variable environments in the future. Sorghum offers a unique opportunity for improvement because of the availability of the vast National Plant Germplasm System (NPGS) collection (>40,000) of natural accessions that can be used to mine essential traits. Additionally, a pedigreed mutant library, derived from the inbred line BTx623, is available. A core collection of 256 lines from this library has been sequenced, revealing over 100,000 nonsynonymous mutations that can change the function of specific proteins. The mutant library also displays a great diversity of phenotypes, many of which may have potential in sorghum improvement, thus providing a unique resource for discovering novel traits in sorghum. Furthermore, sorghum employs the same efficient NADP-ME type of C4 photosynthesis as maize; therefore, it should have similar biomass and grain yields as maize. Due to lack of adequate resources to fully explore the existing sorghum resources for breeding, however, sorghum yield has been stagnant since the 1970s while maize yield continues to improve. There is an urgent need to mine both natural sorghum collections and mutant populations for superior traits to enhance sorghum biomass and grain yield to make it more profitable to grow sorghum. Some of the production problems sorghum growers currently face are cool soil and ambient air temperatures during early season planting, and pre- and post- flowering water stress. Enhanced field germination and excellent seedling vigor are hallmarks of cold tolerance. Recently, high seedling root biomass was identified as an important trait associated with early season cold tolerance of sorghum. Furthermore, early season cold tolerance is important because recent studies have indicated that earlier planting of sorghum can potentially minimize yield losses due to sugar cane aphid infestation. Therefore, research on sorghum to enhance early season germination and vigor is critical for improved sorghum production. The proposed research is relevant to the NP 301 Action Plan, Component 1: Crop Genetic Improvement, Problem Statements 1A: Trait discovery, analysis, and superior breeding methiods and 1B: New crops, varieties, and enhanced germplasm with superior traits.
Objective 1, Sub-objective 1A: Researchers in Lubbock, Texas identified 10 sorghum lines from the highlands of Ethiopia that have excellent cold tolerance, and do not contain the negative agronomic traits associated with the previous Chinese sources. A complete season evaluation of early season cold resiliency shows the Ethiopian lines have less grain yield penalty compared to commonly utilized Chinese cold tolerant sources. ARS scientists are now actively using these new sources in the development of new grain and forage sorghums. Objective 1, Sub-objective 1B: Researchers in Lubbock, Texas identified several positive alleles that contribute to vigorous and longer primary root length during cold treatment of sorghum seedlings using genome-wide association mapping studies. The alleles were discovered as single nucleotide polymorphisms (SNPs) from a set of 190 Ethiopian lines of sorghum. ARS researchers are evaluating the potential of these SNPs as cold tolerant markers for sorghum. Objective 1, Sub-objective 1D: Researchers in Lubbock, Texas developed several mapping populations for dwarf and erect leaf mutants. One dominant erect leaf mutant has been mapped to a region with low recombination frequency and many linked mutations. Researchers plan to further backcross the erect leaf mutant to the wild-type donor parent (BTx623) to reduce the number of linked mutations. Future research includes the use of genome editing techniques to confirm the causal mutation.
1. Development of sugarcane aphid tolerant forages with diverse quality traits. Sorghum used as a forage crop is a major commodity in the United States. Sorghum’s ability to achieve high yields, produce under drought conditions, and have excellent forage quality traits, allows for the crop to be grown in many areas of the country. Unfortunately, the majority of sorghum forages grown today are susceptible to the highly destructive sugarcane aphid. ARS researchers in Lubbock, Texas, developed a diverse set of forage inbreds and hybrids that are highly resistant to the sugarcane aphid using field and greenhouse environments. These breeding lines will be used for further sorghum improvement by ARS researchers. The lines will also be provided to sorghum stakeholders and sorghum breeding programs.
2. Development of sorghum lines with increased seed number. Sorghum is a climate-smart cereal crop that is an essential source of food and feed. It is often cultivated on marginal soils and harsh environments harboring tolerance to high temperature and drought stress. However, a major knowledge gap for sorghum production is limited knowledge on floral development, which could be a major limiting factor contributing to the disruption in grain yield improvement. ARS researchers developed four new inbred lines that possess increased grain number through marker assisted breeding, resulting in significant increases in the number of seeds per panicle. These lines in two elite backgrounds (BTx399 and RTx430) will be made available for public release and will be highly useful for studies of source-sink relationships in sorghum.
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