During previously funded project-years, we identified germplasm lines which contain the best drought tolerance alleles in the USDA-GRIN germplasm collection. We then created segregating populations by crossing twenty accessions ( each had the best tolerance for one drought trait) with a public breeding line that has high seed yield and agronomics. Later we created Multiparent Advanced Generation InterCross (MAGIC) populations to combine multiple tolerance traits. Both biparental and MAGIC populations were advanced to F4-F6 during previously funded project years. In 2023, we examined our 200 best biparental agronomic/genomic selections, along with 20 checks (agronomic/yield, slow and fast wilting) at three field locations. We collected data on canopy wilting, canopy temperature and harvested samples to allow isotopic analysis (C13 ratio and Nitrogen Derived From the Atmosphere). At two locations we collected seed yield and agronomic data. We anticipate future germplasm releases with drought tolerance traits and high agronomic potential. We also created and advanced six MAGIC populations, which combine four different drought tolerance associated trait sources, and collected preliminary agronomic data at one location. This information, along with genomic selection for drought tolerance traits, is being used to identify the best lines for screening for drought tolerance and testing seed yield in 2024 and beyond. An unselected MAGIC population was also advanced to F5 and seed have been increased to permit 2024 experiments. DNA for each line was isolated and submitted for SoySNP6K genotyping, which is essential for future genetic mapping experiments for drought tolerance traits starting in 2024. Stable isotopes of carbon (C13) and nitrogen (N15) provide powerful tools for evaluating genotypic differences in water use efficiency and nitrogen fixation, respectively; however, sampling whole plant biomass methods are very time and resource intensive. To test a possible way to streamline our processes, we compared whole plant biomass samples with seed only samples. We observed very strong agreement between N15 ratios of whole plant samples and seed tissue from three sit- years. These data will simplify the comparison and ranking of genotypes for the fraction of nitrogen derived from the atmosphere through seed samples instead of whole plant samples. We have fully completed all project deliverables for the first year of this project.

Our work identifying and deploying the best possible genetic tolerance to drought stress is in the long term interest of farmers. The results of our studies will inform ongoing breeding efforts, and we are working towards germplasm releases with confirmed drought tolerance and acceptable yield/agronomics. These germplasm release will be made available to public and private breeders to begin incorporation of improved drought tolerance into advanced cultivars.