Foliar-Applied Seaweed Extract Derived from Ascophyllum nodosum Regulated Plant Growth and Biochemical Attributes of Sorghum (Sorghum bicolor L.) Plants Exposed to Drought at Various Growth Stages

Seaweed extract (SE) is a promising natural biostimulant for enhancing plant tolerance to drought stress, but its effectiveness in alleviating drought stress in sorghum (Sorghum bicolor L.) remains uncertain. Addressing this knowledge gap is crucial for developing sustainable strategies to improve drought tolerance in sorghum. The present work was conducted to understand the physiological and biochemical changes of sorghum (Payam cultivar) during drought and the effect of SE application. The experiment followed a split-plot design, with irrigation as the main plot and SE as the sub-plot, with three replicates in 2020 and 2021. Drought was imposed by stopping irrigation at heading (BBCH 51), anthesis (BBCH 61), and maturity (BBCH 71). SE was applied as foliar spray at rates of 2 and 4 L ha-1. Stopping irrigation at BBCH 51 had a greater impact than BBCH 61 and BBCH 71. In non-SE treatments, BBCH 51 significantly (P <= 0.05) led to decreased biological yield (33%), seed yield (30%), thousand seed weight (TSW, 26%), seed protein (18%), SPAD value (15%), relative water content (RWC, 19%), but increased superoxide dismutase activity (SOD, 192%) and catalases activity (CAT, 186%), malondialdehyde (MDA, 127%), and proline (63%). However, at a rate of 4 L ha-1, SE effectively regulated drought stress boosting plant yield, photosynthesis index, RWC, and proline levels. It reduced MDA levels, indicating mitigated oxidative damage. The heat map analysis indicated that SOD, CAT, and MDA were particularly sensitive to both drought and SE. These findings highlight the potential of SE as a natural biostimulant to enhance the growth and resilience of sorghum plants during different growth stages under drought conditions.