Research Project: Discovery and Improvement of Traits to Enhance Sorghum as a Multiple Purpose Crop

Location: Plant Stress and Germplasm Development Research

2020 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 1B: DNA markers were developed by researchers in Lubbock, Texas, to identify early season cold tolerance, brown midrib (bmr), multi-seed (msd), and sparse bloom traits in sorghum. These traits are important environmental and compositional traits for the sorghum grain and forage industries. The DNA markers were confirmed to function in multiple genetic backgrounds, which strengthens their utility and importance to sorghum breeding and genetics programs. Objective 1: Sub-objective 1D-E. We continued to construct mapping populations for the msd trait, erect leaf, and new dwarfing traits in sorghum. Mapping populations consist of both recurrent backcrossing to the original mutant population parent (BTx623), as well as diverse breeding populations. Objective 2: Sub-objective 2A-B. Field experiments were performed for agronomic evaluation of advanced near isogenic lines (NILs) with the multi-seed trait. Researchers analyzed floral architecture and agronomic performance in relation to standard, non-mutant breeding lines. Researchers also developed advanced breeding lines utilizing a common parent with sugarcane aphid resistance, and diverse Ethiopian germplasm. Breeding lines have been screened for sugarcane aphid resistance and cold tolerance using in-house genetic markers and selected lines will be crossed with elite grain sorghum females for hybrid evaluation in subsequent years.

Accomplishments
1. Identification of the first gene controlling grain size in sorghum. Grain size is an important trait for grain yield and commercial processing. It is a complex trait controlled by a large number of genes. However, none of the specific genes have been identified. Rather, large segments of chromosomes, which contain multiple genes, have previously been identified. ARS scientists at Lubbock, Texas, in collaboration with scientists from the Institute of Crop and Nuclear Technology Utilization, Zhejiang Academy of Agricultural Sciences in China identified a gene called SbGS3, which proved to be a key regulator of sorghum grain size. The identification of SbGS3 and its function significantly advances our understanding of the regulatory mechanisms of grain size in sorghum. Furthermore, the SbGS3 gene provides a target to manipulate grain size and increase yield through genome editing because elimination of the gene function is associated with large grain size.

2. Development of early season cold tolerance genetic markers. ARS researchers in Lubbock, Texas, in collaboration with Kansas State University have identified DNA variants that contribute to early season cold tolerance in sorghum. DNA markers were developed and the markers were confirmed to function in multiple genetic backgrounds. The markers were also utilized as a selection tool for identifying six advanced backcross lines that are now being evaluated and used by public and private plant breeding programs. Additionally, cold tolerance genetic markers are actively being used in the in-house sorghum breeding program for the development of high yielding sorghum with diverse genetic backgrounds.

Review Publications
Bangshing, W., Haoxi, C., Yingli, Z., Yun, S., Wannian, Y., Chen, J., Xin, Z., Huazhong, S. 2019. The DEAD-box RNA helicase SHI2 functions in repression of salt-inducible genes and regulation of cold-inducible gene splicing. Journal of Experimental Botany. 71(4):1598–1613. https://doi.org/10.1093/jxb/erz523.
Dampanaboina, L., Jiao, Y., Chen, J., Gladman, N.P., Burow, G.B., Hayes, C.M., Christensen, S.A., Burke, J.J., Ware, D., Xin, Z. 2019. Sorghum MSD3 encodes omega-3 fatty acid desaturase that regulates grain number by reducing jasmonic acid levels. International Journal of Molecular Sciences. 20(21):5359. https://doi.org/10.3390/ijms20215359.
Gladman, N.P., Jiao, Y., Lee, Y., Zhang, L., Chopra, R., Regulski, M., Burow, G.B., Hayes, C.M., Christensen, S.A., Dampanaboina, L., Chen, J., Burke, J.J., Ware, D., Xin, Z. 2019. Fertility of pedicellate spikelets in sorghum is controlled by a jasmonic acid regulatory module. Nature Plants. 20(19). https://doi.org/10.3390/ijms20194951.
Burke, J., Emendack, Y., Hayes, C.M., Xin, Z., Burow, G.B. 2019. Registration of five post-flowering drought tolerant grain sorghum lines with early season cold tolerance. Journal of Plant Registrations. https://doi.org/10.3198/jpr2019.02.0010crg.
Marla, S., Burow, G.B., Chopra, R., Hayes, C.M., Olatoye, M., Felderhoff, T., Hu, Z., Raymundo, R., Perumal, R., Morris, G. 2019. Genetic architecture of chilling tolerance in sorghum dissected with a nested association mapping population. G3, Genes/Genomes/Genetics. 9:4045-4057. https://doi.org/10.1101/622894.
Mauget, S.A., Kothari, K., Leiker, G.R., Emendack, Y., Xin, Z., Hayes, C.M., Ale, S., Baumhardt, R.L. 2020. Optimizing dryland crop management to regional climate. Part II: U.S. Southern High Plains sorghum production. Frontiers in Sustainable Food Systems. 3:119. https://doi.org/10.3389/fsufs.2019.00119.
Naoura, G., Nerbewende, S., Atchozou, E., Emendack, Y., Hassan, M., Echevarria Laza, H.J., Tabo, R. 2019. Assessment of agro-morphological variability of dry-season sorghum cultivars in Chad as novel sources of drought tolerance. Nature Scientific Reports. 9:19581. https://doi.org/10.1038/s41598-019-56192-6.
Gitz, D.C., Baker, J.T., Xin, Z., Lascano, R.J., Stout, J.E. 2019. Systematic error introduced into sorghum yield data: Does the multiseed (msd) trait increase sorghum seed yield? American Journal of Plant Sciences. 10:1503-1516. https://doi.org/10.4236/ajps.2019.109106.
Zou, G., Zhou, L., Zhai, G., Ding, Y., Lu, P., Liu, H., Zhen, X., Liu, X., Zhang, L., Xin, Z., Chen, H. 2019. A high throughput method for screening deep-seeding tolerance in sorghum. Seed Science Research. https://doi.org/10.1007/s10722-019-00835-0.