Genomics and Applied Biology 2024, Vol.15, No.6, 296-306 http://bioscipublisher.com/index.php/gab 301 By understanding these biochemical and molecular responses, researchers can develop strategies to enhance drought tolerance in soybean varieties, ensuring better yield and productivity under water-limited conditions. 4 Screening Methods for Drought Tolerant Varieties During Flowering and Podding 4.1 Field screening techniques for identifying drought tolerant varieties Field trials are essential for evaluating the drought tolerance of soybean varieties, particularly during the critical flowering and podding stages. These trials should be designed to simulate drought conditions accurately and assess the physiological and agronomic responses of different soybean genotypes. A randomized complete block design (RCBD) with multiple replications is recommended to ensure the reliability of the results (Wang et al., 2022a). To target the flowering and podding stages, drought stress can be imposed by controlling soil moisture content. For instance, maintaining soil moisture at 40% of field capacity can effectively simulate drought conditions. Additionally, the use of pot experiments to control soil moisture and evaluate survival percentages after drought stress can provide valuable insights into the drought tolerance of different soybean varieties (Fatema et al., 2023). Evaluating agronomic traits under drought conditions is crucial for identifying drought-tolerant soybean varieties. Key traits to assess include yield, flower retention, and pod number. Drought stress during the flowering stage can significantly impact these traits, leading to reduced yield and flower retention (Buezo et al., 2018). For instance, studies have shown that drought stress can adversely affect pod and seed production, grain size, and seed yield, with genotypic variations being evident (Wang et al., 2022a). High-yielding varieties under drought conditions often exhibit enhanced photoprotective defenses and higher intrinsic water use efficiency, which contribute to their productivity (Wang et al., 2022b). Moreover, physiological traits such as leaf area, plant height, and membrane stability index (MSI) should also be evaluated, as they are indicative of a plant's ability to withstand drought stress. Varieties that maintain higher values of these traits under drought conditions are considered more drought-tolerant (Moloi and Merwe, 2021; Wang et al., 2024). In summary, field trials targeting the flowering and podding stages, combined with the evaluation of key agronomic and physiological traits, are essential for screening and identifying drought-tolerant soybean varieties. These methods provide a comprehensive understanding of the genotypic responses to drought stress and aid in the development of resilient soybean cultivars. 4.2 Controlled environment screening Controlled environment screening is essential for understanding the drought tolerance of soybean varieties, particularly during critical reproductive stages such as flowering and podding. Growth chamber and greenhouse experiments allow for precise control of environmental variables, facilitating the study of physiological and biochemical responses to drought stress. For instance, a study conducted in a greenhouse setting revealed significant reductions in leaf number, plant height, stem girth, leaf area, and flower number under drought conditions, highlighting the sensitivity of these traits to water deficit during the flowering stage (Puobi et al., 2023). Another study emphasized the importance of maintaining high water use efficiency and biomass accumulation to sustain pod number and seed yield under drought stress, which was observed in certain drought-tolerant soybean cultivars (Gebre et al., 2022). To simulate field conditions and induce drought stress, various techniques such as polyethylene glycol (PEG) treatment and controlled water deficit are employed. These methods help in creating a consistent and reproducible drought environment for screening purposes. For example, a study used controlled soil moisture content to simulate different degrees of drought, revealing that drought-tolerant varieties exhibited less reduction in physiological traits compared to drought-sensitive ones (Wang et al., 2022a). Similarly, another experiment utilized pot trials with controlled watering regimes to assess the drought tolerance of soybean genotypes, identifying key traits such as leaf area index (LAI) and root-to-shoot ratio (RSR) as reliable indicators of drought resistance (Yan et al., 2020).
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