Location: Plant Stress and Germplasm Development Research
2023 Annual Report
Objectives
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.
Approach
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.
Progress Report
This will serve as the final report for this project as it terminated in 2022 and was replaced with a new project (3096-21000-024-000D). Throughout this project plan, ARS scientists in Lubbock, Texas, have conducted over 18 field or laboratory studies. For Sub-objective 1A, we developed and tested 35 sorghum lines derived from Ethiopian and Sudanese germplasm that have varied levels of improved cold tolerance combined with sugarcane aphid tolerance. Advanced hybrid evaluation of the newly developed sorghum lines suggests that many lines produce high yield grain sorghum hybrids with acceptable agronomics such as reduced plant height and days-to-anthesis between 50 and 65 days. Researchers are now actively using these new sources in the development of new grain and forage sorghums. For Sub-objective 1B, we continued laboratory analysis of root traits in sorghum. Researchers performed multiple early-season field trials evaluating select sorghum lines for cold tolerance and early-season plant growth. Researchers have identified new sorghum germplasm with increased root biomass under cool conditions to be used in breeding programs. For Sub-objective 1D, researchers in Lubbock, Texas, developed and tested several multi-seed isogenic grain inbred lines and hybrids in four unique production environments throughout Texas. Results indicate that grain hybrids with the multi-seed trait have increased grain numbers. Grain size varied depending on the genetic background. Grain yield on a per acre basis varied greatly between wild-type and multi-seed hybrids. Grain yield differences between multi-seed hybrids and wild-type hybrids have been inconclusive, with some environments showing a yield increase, while other environments producing a yield decrease. For Sub-objective 1E, we discovered, isolated, and tested dwarf and erect leaf mutant sorghum from a sorghum mutant population. We are now actively using these new sources in the development of new grain and forage sorghums. For Sub-objective 2A, researchers developed and investigated two sorghum mapping populations containing the multi-seed traits with erect leaf architecture, plant height, improved harvest index and novel plant signaling traits. Genetic mapping and characterization of physiological traits linked to increased seed number in inbred lines has been performed. Researchers have identified improved sorghum lines from the population and are actively using the breeding lines in the development of improved sorghum. For Sub-objective 2B, we developed and tested new sorghum lines with sugarcane aphid tolerance. Multi-year results demonstrate that the new sorghum lines produce high yielding grain sorghum hybrids with excellent aphid tolerance. Sugarcane aphid tolerance has been confirmed by greenhouse evaluations and genetic marker confirmation. ARS and sorghum seed companies are now actively using these new resources in the development of new sugarcane aphid resistant grain sorghum hybrids.
Accomplishments
1. Whole genome sequencing of 1000 sorghum mutants. The complete whole genome sequencing of an organism is a powerful tool scientists can use to better understand important traits and genes in plants. Discoveries made using whole genome sequencing include gene discovery, genetic marker development, and the development of superior crops. ARS scientists in Lubbock, Texas, in collaboration with government, industry, and university partners, sequenced over 1000 sorghum mutants utilizing the newest genetic sequencing technologies. This effort, together with the previously sequenced 250 mutants, uncovered over 10 million induced mutations that covered 98% of sorghum's annotated genes. Additionally, the sequencing also discovered 610,320 mutations in the promoter and enhancer regions of 18,000 and 11,790 genes, respectively. These sequenced mutants provide a critical resource to study the functions of genes and their regulatory elements. This work is foundational for genomic studies in sorghum and other grasses, and sorghum improvement.
2. Development of diverse sorghum germplasm with sugarcane aphid resistance. Sorghum is an important cereal grain for many producers in the U.S. due to its inherit drought tolerance, disease resistance, and high grain yield potential. Although resistant to many common pests, the vast majority of sorghum today is highly susceptible to the sugarcane aphid. If left untreated, grain yield losses in sorghum can be devasting, often resulting in a complete loss of the crop. In fact, sorghum acres declined a minimum of twenty percent in 2015 due to yield reductions and harvest issues associated with the aphid. ARS scientists in Lubbock, Texas, developed sugarcane aphid resistant sorghum utilizing materials from Ethiopia and Sudan. These newly developed sorghum breeding lines possess excellent aphid resistance. Additionally, the breeding lines have important agronomic traits such as drought tolerance, early-maturity, and general adaptation to production environments in Texas and Kansas. The development and use of sugarcane aphid resistant germplasm utilizing these lines and other sorghum lines developed by U.S. breeding programs increased sorghum acres in the U.S by over one million acres and provided millions of dollars of additional economic impact to sorghum producers. These breeding lines provide much needed genetic resistance to sugarcane aphid in diverse genetic backgrounds.
3. Doubling seed number in sorghum using mutants. Grain yields of sorghum in the U.S. have been relatively stagnant for approximately forty years. Researchers have been actively looking for new traits that improve grain yield in sorghum. The utilization of mutants in a plant improvement program can be a novel source of genetic and phenotypic variation that ultimately improves grain and forage yields. ARS scientists in Lubbock, Texas, identified an innovative trait known as multi-seed from a sorghum mutant population. The multi-seed mutants contain at least twice the number of seeds compared to normal sorghum lines. The multi-seed trait was backcrossed into two agronomically important inbred lines for continued evaluation and testing. ARS scientists intend to release these materials as donor germplasm for breeding programs, and for additional hybrid testing evaluating the grain yield potential of the multi-seed trait in grain sorghum.
Review Publications
Emendack, Y., Sawadogo, N., Ramadjita, T., Laza, H. 2023. Assessment of photoperiod sensitivity and the effect of sowing date on dry-season sorghum cultivars in Southern Chad. Agronomy Journal. 13(3). Article 932. https://doi.org/10.3390/agronomy13030932.
Mendu, L., Jalathge, G., Dhillon, K., Singh, N., Balasubramanian, V., Fewou, R., Gitz, D.C., Chen, J., Xin, Z., Mendu, V. 2022. Mutation in Endo-ß-1,4-Glucanase (KORRIGAN) is responsible for thick leaf phenotype in sorghum. Plants. 11(24). https://doi.org/10.3390/plants11243531.
Khan, A., Khan, N., Bean, S.R., Chen, J., Xin, Z., Jiao, Y. 2023. Variations in total protein and amino acids in the sequenced sorghum mutant library. Plants. 12(8). https://doi.org/10.3390/plants12081662.
Chaudhuri, S., Roy, M., McDonald, L., Emendack, Y. 2023. Land degradation–desertification in relation to farming practices in India: An overview of current practices and agro-policy perspectives. Sustainability. 15(8). https://doi.org/10.3390/su15086383.
