Counteracting Heat, Salinity, and Osmotic Stresses by Reconciling Seed Size and Sowing Depth for Bolstering Germination and Seedling Growth of Cluster Bean (Cyamposis tetragonoloba L. Taub.)

Abstract

Under abiotic stresses (AS, heat, salinity, and osmotic stresses), seed germination and seedling growth of legumes like cluster beans are critical phases of the crop growth cycle that determine their productivity. Research gaps exist regarding the impacts of seed size, sowing depth, and soil pH on the germination, root, and shoot growth attributes of cluster beans when exposed to AS. Five different trials were executed to assess the comparative performance of cluster bean seed sizes (small, medium, and large) in response to different regimes of temperature (T, 10, 20, and 30 degrees C), salinity (SS, 50, 100, 150, and 200 mM), osmotic stress (OS, 0.2, 0.4, 0.6, 0.8, and 1.0 Mpa), soil pH (5, 6, 7, 8, 9, and 10), and sowing depths (SD, 0, 2, 4, 6, and 8 cm). The response variables included germination (GP), germination index (GI), and time taken to 50% germination (TG), along with length, fresh, and dry weights of the shoot and root of the cluster bean. The results exhibited that large-size seeds sown at 4 cm depth remained unmatched by recording the maximum GP and GI up to 20-30 degrees C temperature, 0-50 mM salinity level, 0-0.4 Mpa osmotic stress, and 6-7 pH. The same range of employed treatments also remained effective in a pronounced reduction of time taken to the TG. Moreover, cluster bean largesize seeds sown in 4 cm depth depicted the maximum root and shoot attributes, whereas smaller seed sizes sown in 0, 6, and 8 depths when exposed to 10 degrees C temperature, 100-200 mM SS levels, soil pH (5, 9, and 10), and 0.6, 0.8, and 1.0 Mpa of OS recorded significantly reduced shoot and root traits. Thus, these findings reveal the feasibility of alleviating moderate levels of AS for cluster beans with large seed sizes and sowing depth reconciliation under semi-arid conditions.