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

Location: Plant Stress and Germplasm Development Research

2019 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-B: Identification of Molecular Markers for Cold Tolerance. Leaf material from genotypes showing enhanced seedling vigor in early-planted field trials was used for deep sequencing analysis and resulted in the identification of new molecular markers associated with cold tolerance. A growth chamber study was conducted on 250 mutant and germplasm entries to screen for root morphology phenotypes using photogrammetry. This study identified a number of different root growth phenotypes that will be scored for heat and drought tolerance in FY 2020. Objective 1. Sub-objective 1D: Ten new advance backcrossed sorghum lines with multiseededness trait were developed and are undergoing detailed field testing to determine if the multiseeded trait increase grain yield under field conditions. Objective 1. Sub-objective 1E: Creation of Mapping Populations for Dwarf Phenotypes. Mapping populations (F2) were developed for several dwarf mutants and some of the population displayed the expected segregation ratio for the dwarf phenotype. These populations will help identify novel dwarf genes to improve sorghum breeding. Objective 2. Sub-objective 2A. Improved Grain Quality Traits Using Marker-assisted Selection. The waxy trait in sorghum alters the starch composition of the grain such that ethanol plants and animal feeding operations can more effectively utilize the starch within sorghum grain. Eighty waxy hybrids, 4 waxy female parents by 20 waxy male parents, were created. These hybrids provide a rich source to breed the much-needed waxy sorghum hybrids.

Accomplishments
1. DNA markers for cold tolerance in sorghum identified improved cold tolerance for germination and seedling vigor is important for early planting on the U.S. Southern Great Plains. Earlier planting allows growers to take advantage of the early season stored soil moisture, provides flexibility in crop rotation schemes, and can expand the range of sorghum production. However, it is often difficult to evaluate in the field and greenhouse studies have proven to be of little value. ARS scientists in Lubbock, Texas, along with collaborators at Kansas State University, identified DNA markers associated with enhanced cold tolerance using high-throughput, deep sequencing analysis of multi-parental mapping populations. These markers will be employed by breeders to select for cold tolerance in a wide-range of sorghum varieties to identify candidate germplasm for phenotyping and breeding experiments aimed at improving cold tolerance. This information will shorten breeding time and allow for a comprehensive selection of cold tolerance germplasm in a large number of germplasm accessions, thus dramatically improving the odds of identifying key cold tolerance traits and introgressing those traits into elite germplasm at significantly smaller time-frame than conventional screening, selection, and breeding apporaches.

2. Development of DNA markers for brown midrib trait. Brown-midrib (bmr) in sorghum is a trait associated with increased forage digestibility and ethanol yield of sorghum biomass. ARS scientists at Lubbock, Texas, developed molecular markers for selection of this trait. These markers can be used to select this trait efficiently by sorghum breeders to develop better forage and biomass sorghum.

Review Publications
Chen, J., Burke, J.J., Xin, Z. 2018. Chlorophyll fluorescence analysis revealed essential roles of FtsH 11 protease in regulation of the adaptive responses of photosynthetic systems to high temperature. Biomed Central (BMC) Plant Biology. doi:10.1186/s12870-018-1228-2.
Burow, G.B., Chopra, R., Sattler, S.E., Burke, J.J., Acosta Martinez, V., Xin, Z. 2019. Deployment of SNP (CAPS and KASP) markers for allelic discrimination and easy access to functional variants for brown midrib genes bmr6 and bmr12 in Sorghum bicolor. Molecular Breeding. 39:115. https://doi.org/10.1007/s11032-019-1010-7.
Burow, G.B., Chopra, R., Hughes, H.J., Burke, J.J., Xin, Z. 2018. Marker assisted selection in sorghum using KASP assay for detection of single nucleotide polymorphism/insertion deletion. Methods in Molecular Biology. 1931:75-84. https://doi.org/10.1007/978-1-4939-9039-9_6.
Burke, J.J., Emendack, Y., Hayes, C.M., Xin, Z., Burow, G.B. 2018. Registration of four post-flowering drought tolerant grain sorghum lines with early season cold tolerance. Journal of Plant Registrations. doi:10.3198/jpr2017.12.0086crg.
Emendack, Y., Burke, J.J., Bean, S.R., Wilson, J.D., Hayes, C.M., Laza, H. 2018. Composition, functional components, and physical characteristics of grain from staygreen and senescent sorghum lines grown under variable water availability. Cereal Chemistry. 2018:1-12.
Emendack, Y., Burke, J.J., Echevarria Laza, H., Sanchez, J., Hayes, C.M. 2018. Abiotic stress affects on sorghum leaf dhurrin and soluble sugar contents throughout plant development. Crop Science. 58:1706-1716. doi:10.2135/cropsci2018.01.0059.
Emendack, Y., Burke, J.J., Sanchez, J., Echevarria Laza, H., Hayes, C.M. 2018. Agro-morphological characterization of diverse sorghum lines for pre-and postflowering drought tolerance. Australian Journal of Crop Science. 12(01):135-150.
Hayes, C.M., Armstrong, J.S., Limaje, A., Emendack, Y., Bean, S.R., Wilson, J.D., Xin, Z. 2018. Registration of R.LBK1 and R.LBK2 sorghum germplasm with resistance to the sugarcane aphid [Melanaphis sacchari (Zehntner)]. Journal of Plant Registrations. 13:91-95 (2019).
Chen, J., Xin, Z., Echevarria Laza, H.J. 2019. Registration of BTx623dw5 - a new sorghum dwarf mutant. Journal of Plant Registrations. 13:254-257. https://doi.org/10.3198/jpr2018.09.00058crgs.
Jiao, Y., Lee, Y., Gladman, N., Chopra, R., Christensen, S.A., Burow, G.B., Hayes, C.M., Burke, J.J., Ware, D., Xin, Z., Regulski, M. 2018. MSD1 regulates pedicellate spikelet fertility through the jasmonic acid pathway in sorghum. Nature Communications. 9(1):822. https://doi.org/10.1038/s41467-018-03238-4.
Xu, Y., Li, J., Moore, C., Xin, Z., Wang, D. 2018. Physico-chemical characterization of pedigreed sorghum mutant stalks for biofuel production. Industrial Crops and Products. 124:806-811.
Wang, M.L., Xin, Z., Burow, G.B., Chen, J., Vankus, P.J., Pinnow, D.L., Tonnis, B.D., Cuevas, H.E., Yu, J. 2017. Evaluation of sweet sorghum accessions for seedling cold tolerance using both lab and field cold germination test. Journal of Agricultural Science and Botany. 1(1):1-8.
Chen, J., Zou, G., Xin, Z. 2019. Development of a pedigreed sorghum mutant library. In: Walker, J.M. Methods in Molecular Biology. Humana Press, Clifford, New Jersey. 1931:61-73. https://doi.org/10.1007/978-1-4939-9039-9_5.
Xin, Z., Chen, J., Jiao, Y., Gladman, N., Hayes, C.M., Burow, G.B., Emendack, Y., Burke, J.J. 2018. Registration of BTx623ms8 - a new and easily identifiable nuclear male sterile mutant in sorghum. Journal of Plant Registrations. https://doi.org/10.3198/jpr2017.09.0063crgs.