Location: Plant Stress and Germplasm Development Research
2022 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
Objective 1, Sub-objective 1A: Researchers in Lubbock, Texas, developed 35 sorghum lines derived from Ethiopian and Sudanese germplasm that have varied levels of improved cold tolerance combined with sugarcane aphid tolerance. Preliminary 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. ARS researchers are now actively using these new sources in the development of new grain and forage sorghums.
Objective 1, Sub-objective 1B: We continued laboratory analysis of root traits in sorghum and performed an early-season field trial evaluating select sorghum lines for cold tolerance and early-season plant growth.
Objective 1, Sub-objective 1D: We evaluated grain yield potential of several multi-seed isogenic grain inbred lines and hybrids. Preliminary results show that grain hybrids with the multi-seed trait have increased grain numbers, similar to the hybrids’ respective inbred lines. Grain size varied depending on the genetic background. Grain yield on a per acre basis varied greatly between wild-type and multi-seed hybrids. Some environments produced higher grain yields with the multi-seed trait, while other environments produced a reduced grain yield. The casual mechanisms for variable grain yield response are still being evaluated, but environmental conditions during crop growth, and method of harvest are two sources of variation identified for further investigation.
Objective 1, Sub-objective 1E: Research continued with the testing of dwarf and erect leaf mutant sorghum. Select lines were evaluated in three unique locations. Data collected include plant height, number of leaves per plant, leaf angle, and grain yield.
Objective 2, Sub-objective 2A: Researchers developed two sorghum mappings combining the multi-seed mutation with erect leaf architecture, plant height, improved harvest index and novel plant signaling traits. Future studies involve genetic mapping and characterization of physiological traits linked to increased seed number in new inbred lines. Additionally, results from this study will allow plant breeders to identify specific plant characteristics, coupled with the multi-seed trait, that produce increased grain yields.
Objective 2, Sub-objective 2B: Research continued on hybrid testing of new sorghum lines developed with sugarcane aphid tolerance. Preliminary results show that many lines produce high yielding grain sorghum hybrids with excellent aphid tolerance. Sugarcane aphid tolerance was confirmed by greenhouse evaluations and genetic marker confirmation.
Accomplishments
1. Novel dwarf gene identified. Dwarf genes in the signaling and biosynthetic pathways of the plant hormone gibberellic acid are the genetic mechanisms producing higher yields in many crops. Such dwarf genes have never been found in sorghum. Instead, breeding semi-dwarf sorghum hybrids requires the combination of several alterative dwarf genes, which limits the full expression of hybrid vigor. The use of alterative dwarf genes helps explain limited yield improvement in sorghum over time. ARS scientists from Lubbock, Texas, discovered new dwarf mutants and their causal mutation in a gene in the gibberellic acid signaling pathway. These novel dwarf mutants may have potential to significantly improve grain yield in sorghum.
2. Release of new sorghum genetic stock to improve yield. Three new sorghum brown mid-rib genetic stocks were developed and publicly released by ARS scientists in Lubbock, Texas. The genetic stocks were isolated from a pedigreed sorghum ethyl methane sulfonate mutagenized sorghum population in BTx623 background. The primary purpose of the germplasm release was to provide new sources of sorghum for the development of improved brown mid-rib forage sorghum. The three new brown mid-rib alleles provide both public and private breeders with a new source of brown mid-rib sorghum, which should improve yields of forage sorghum.
Review Publications
Emendack, Y., Xin, Z., Hayes, C.M., Burow, G.B., Sattler, S.E., Bean, S.R., Smolensky, D. 2022. Registration of 3 new bmr12 sorghum mutants from ems-induced btx623 mutation. Journal of Plant Registrations. 16(2):453-458. https://doi.org/10.1002/plr2.20219.
Gapili, N., Emendack, Y., Baloua, N., Vom Brocke, K., Hassan, M., Sawadogo, N., Amos, D., Reoungal, D., Giles, T., Laza, H. 2020. Characterization of semi-arid Chadian sweet sorghum accessions as potential sources for sugar and ethanol production. Nature Scientific Reports. 10, Article 14947.
Laza, H.E., Kaur-Kapoot, H., Xin, Z., Payton, P.R., Chen, J. 2022. Morphological analysis and stage determination of anther development in Sorghum [Sorghum bicolor (L.) Moench. Planta. 255. Article 86. https://doi.org/10.1007/s00425-022-03853-y.
