High Throughput Phenotypic Evaluation Of Drought-Related Traits In Soybean.

The effects of drought on soybean physiology during reproductive development were evaluated in two experiments. For the first experiment, five cultivars ranging from maturity group II through V were included in well-water (WW) and drought (DR) treatments. The WW treatment was irrigated when the estimated soil-water deficit reached 30 mm, while the drought treatment received irrigation every third time as well-watered field after canopy closure. Beginning at R5, leaf N concentration was measured by taking leaf samples. Pictures of individual plots were taken against a pink board with both green and yellow standards to determine the Dark Greenness Color Index (DGCI). In addition, aerial images were taken using a 2-diameter balloon or a kite for aerial DGCI measurements. DGCI values are directly related to the intensity of green leaf color, which is associated with leaf N concentration. The results showed that leaf N concentration was highly associated with ground DGCI, and ground DGCI significantly agreed with aerial DGCI. This opens up the possibility of identifying genotypes that senesce quickly due to drought stress. In the second experiment, a line source experiment was established with genotypes previously characterized as fast or slow wilting. The experiment included 3 water treatments: well watered (WW), medium watered (MW), and rainfed (RF). Carbon isotope discrimination (Δ¹³C) was determined from leaves sampled at late R5 and from seed at harvest as a surrogate measure for water use efficiency. The results indicated that Δ¹³C values for soybean leaf and seed decreased with increasing drought stress (i.e., higher water use efficiency). Likewise, slow wilting genotypes had lower Δ¹³C values for soybean seed compared to fast wilting genotypes. These results indicate that DGCI measurements from aerial platforms and Δ¹³C measurements of leaf and seed hold promise for characterizing drought-related traits in soybean.