Development of Heat-Tolerant Soybean for the Midsouth
In a previous article posted on this website, the potential effects of increasing temperatures on soybean development and seed quality are discussed. If the scenario outlined in that article comes about, crop production in the southern U.S. will have to adapt. That likely will happen through changes in production practices and in the genetics of crop plants that will allow them to produce a profitable and useable yield under conditions of increasing air temperatures. With soybeans in the Midsouth, this has already come about to some extent by using the now-conventional Early Soybean Production System (ESPS), which is designed to avoid some of the summer heat that is common in the region. However, the weather-related occurrence of damage to maturing and mature soybean seed in this system is problematic for producers that are affected by inclement weather immediately preceding and following maturity.
Dr. Rusty Smith and colleagues have been addressing the genetic component of soybean adaptation to increasing heat. They initiated genetic studies and breeding programs to identify specific traits affected by high temperatures, determined the inheritance of tolerance to heat, and developed improved soybean lines with heat tolerance (manifested as improved seed quality). In one of their studies [Metabolomics, Feb. 2016, 12:28], a greater abundance of antioxidant metabolites in a heat-tolerant line indicates that the identified compounds are likely associated with/partially responsible for the greater tolerance of high temperature-tolerant lines to high temperatures during seed development.
The result of the above work has been the development of improved heat-tolerant soybean germplasm lines that are or soon will be available to both commercial and public soybean breeders and researchers. One such product is soybean line DS31-243 (PI 700941), an early MG IV, non-GMO line that has reduced seed damage relative to susceptible commercial and public soybean varieties. This reduced damage includes less visual mold, stink bug feeding, discoloration, wrinkling, purple seed stain, and green seed when subjected to hot humid conditions during plant maturation and seed dry down. This line was officially released by USDA in a letter dated Apr. 26, 2022, and is the first U.S. germplasm release that addresses this problem. The tolerance in this released line was derived from PI 587982A, a soybean accession from China. Results from research using this PI are reported in an article titled “Quantitative trait locus mapping for resistance to heat-induced seed degradation and low seed phytic acid in soybean” by Gillman, Chebrolu, and Smith (Crop Sci. 2021; 61:2023-2035).
In a Phomopsis seed decay (PSD) nursery at Stoneville, Miss. that featured inoculation with pathogen spores after growth stage R5 followed by daily overhead irrigation, plus a 2-week delay in harvest after stage R8, DS31-243 had a significantly lower percentage of seed damage and PSD than the PSD-susceptible check and the commercial varieties used in the studies. In both nonirrigated and irrigated studies conducted at Stoneville in 2019 and 2020, seed from DS31-243 that was harvested 2 weeks after R8 had less wrinkling, visual mold, and purple seed stain than commercial varieties grown in the studies. In studies conducted at Jackson, Tenn. in 2020 and 2021, DS31-243 was resistant to frogeye leaf spot. In tests that were conducted at West Lafayette, Ind., DS31-243 was resistant to races 1, 3, 4, and 7 of Phytophthora root and stem rot, while having mixed reactions to races 17 and 25. Based on results from the the Uniform Soybean Tests-Southern States that were conducted from 2017 to 2019, the line was determined to be resistant to the pathogen that causes stem canker.
Products such as the above can provide developers of new soybean varieties the improved genetic traits that can be incorporated into future varieties to partially offset the negative effects of the hotter production environments that will affect maturing/mature soybean seeds in Midsouth soybeans in the coming years. To obtain seed of this line (which is freely available), contact Dr. J. R. Smith (rusty.smith@usda.gov) at the USDA-ARS Crop Genetics Research Unit in Stoneville. Dr. Smith’s contact information is contained in the above-linked release letter.
Composed by Larry G. Heatherly, Sep. 2022, larryh91746@gmail.com