Updated June 5, 2023:
Drought has been a major problem facing farmers. Historically, drought has been problematic later in the growing season, around August and primarily a problem in the Southeast. In 2020, severe drought conditions were observed from the Midwest to the Southeast. In late August of 2020 nearly half of Iowa was reported to be in a “severe or extreme drought,” according the USDA’s weekly drought monitor, right at the time soybeans were setting pods. In 2021, the northern Plains was probably the worst hit area. According to the U.S Drought Monitor, large areas of North Dakota, South Dakota and Minnesota were suffering from some sort of drought conditions in May. So, it is not a question of if a drought will occur, it is more about when it will occur and how much damage it causes. Team Drought now has breeders in Iowa, Missouri, North Carolina, Georgia, Kansas, Texas and Arkansas, which spans maturity groups II-VIII. Significant progress has been made in the way of line development, identifying genomic markers for drought tolerance and development of drought tolerate inoculum. The purpose of this project is to expand on earlier successes and keep the drought breeding pipeline flowing to the commercial sector and the farmer.

Project Highlights:
1). Two major slow wilting genes on Chr. 6 and 10 from an exotic line PI 567731 were isolated into near-isogenic backgrounds. Yield trials on the near-isogenic lines found that a single slow wilting gene can improve yield by 11-14% and the two genes together can improve yield by 20% under drought stress. Currently, we are incorporating 2 slow wilting genes into high protein and high oleic elite lines by marker-assisted backcrossing. Currently, they are at BC2F1 generation and we will continue for 2 more generation of backcrossing. 2). The new breeding lines with introgressed root length density gene from an exotic line (PI 561271) were tested in the yield trials under drought and non-stress conditions at 3 locationsin 2020 and 2021. The gene incorporation line showed a yield advantage (18%) under rainfed conditions. 3). One significant QTL associated with root length and root surface area was identified on Chr. 7 from a wild soybean derived RIL population. The donor allele is from the wild accession (PI 483460B). This result was published in the peer-reviewed journal “Frontiers in Plant Science”. This gene can be used to develop larger soybean root to improve water uptake in the dry soils. 4). The near-isogenic lines for 2 major slow-wilting genes on chromosome 6 and 10 were tested in yield trials under drought and non-stress conditions in 2020. A single slow wilting gene can improve yield by 11-14% and the two genes together can improve yield by 20% under drought stress. 5). To improve the selection efficiency for drought tolerance in a breeding program, the whole genome approach for selection was explored to select for drought tolerance. Using the diversity panel that was phenotyped previously as a reference population, cross-validation results for the genomic prediction of drought tolerance was achieved from 55-57% with four prediction models. 6). To develop a methodology for evaluation of drought tolerance, we are testing transpiration rates among soybean lines with slow and fast canopy wilting under normal and stressed conditions using new sensing technology. A diverse 450 line mini-core panel was evaluated by hyperspectral reflectance using an ASD Field Spec Spectroradiometer, which resulted in areas of differential reflectance between different wilt scores. These differential areas of interest are promising for detecting wilt score in the field and provide more information beyond visual capabilities. 7). The complete analysis of nodule counts between the irrigated and rainfed conditions for both Woodruff (slow-wilting) and N7003CN indicated more nodules (both taproot and total nodules) were formed in both cultivars when inoculated with the TXVA strain compared to those with Cell-Tech and the un-inoculated control, under drought stress. In addition, the slow-wilting cultivar (Woodruff) and the TXVA strain show synergetic effects on yield compared to the un-inoculated control, although the difference between the TXVA and Cell-Tech treatments is not statistically significant. 8). Eight QTLs were identified on 7 Chromosomes related to slow wilting. Three of the eight QTLs that were identified collocate with significant SNPs from the drought GWAS that was performed by Steketee et al. (2020)(previous Team Drought study). Two of the QTLs identified on Chromosome 13 were within 10kb of gene models that have been reported to be associated with drought tolerance by Li et al. (2019) (previous Team Drought study). 9). A QTL, LG-H, derived from PI 416937, located on Chr 12 was reported in a previous study, which accounted for 27% of phenotypic variation for canopy wilting. Near-isogenic lines for this QTL were developed by backcrossing and were evaluated in 2021, data analysis will begin after harvest. Results from this study will allow for a better understanding of the mechanism on Chromosome 12 that is responsible for drought tolerance. 10). Leaf gas exchange results from the 2020 open-top chamber study showed a 20-30% increase in water use efficiency (WUE) in breeding lines developed from crosses between Fiskeby III and Fiskeby V and the agronomically adapted, but drought sensitive Holladay parent. These results suggest that the leaf trait associated with WUE from the stress tolerant Fiskeby lines has been successfully transferred into elite breeding materials. 11) Fifty-seven UM developed promising lines are under evaluation for yield and other agronomic traits in rainfed and irrigated field conditions in Missouri, of which 5 lines have recently (in 2020) been released as cultivars, 8 lines are being tested in 2021 USDA Uniform Trials (UT) and 11 lines are tested in 2021 Drought Uniform Trials across 4 states (AR, KS, MO and NC). The yield plots will be harvested soon and the best performing lines will be identified.