Cobalt enhanced the drought-stress tolerance of rice (Oryza sativa L.) by mitigating the oxidative damage and enhancing yield attributes.

• Drought stress causes a severe oxidative stress in rice plants. • Drought negative effects exacerbate the decline in yield indices and grain nutritional quality. • Cobalt priming of seeds can greatly aid in reducing ROS-induced damage which orchestrated with better growth, yield and nutritional quality of rice under drought stress. Water scarcity is one of the most important abiotic factors limiting rice growth and productivity. The application of nutrients affects various physiological and biochemical mechanisms to curtail water deficiency, but little is known about the ameliorative effects of cobalt (Co) on rice. Our study aimed to investigate the advantageous effects of soaking in Co at the optimum concentration (10 and 44.5 µM) on morpho-physiological traits and oxidative stress, during the vegetative and reproductive stages, also assessing yield attributes, in two rice varieties (Sakha 104, drought-sensitive, and Giza 178, drought-tolerant). Treatments included control (100% field capacity (FC)), moderate drought stress (75 % FC), and severe drought stress (50 % FC) either alone or in combination with Co. A water deficit and oxidative stress affected Giza 178 less than Sakha 104. Co application significantly enhanced the performance of two rice varieties under drought stress by increasing plant height, biomass, water content, tillering, leaf area, pigments (chlorophyll a, carotenoids, total chlorophyll), sugars (soluble sugars, and total carbohydrates), and Co content (shoot and root). Also, Co significantly increased the performance of the antioxidant system by elevating the concentration of total phenols, flavonoids, proline, and antioxidant enzymes (catalase, peroxidase, and polyphenol oxidase), while significantly decreasing chlorophyll b, malondialdehyde, and 2,2-diphenyl-1-picryl-hydrazyl. Yield attributes such as the number of tillers, panicle parameters (number, length, and weight), 100-grain weight, harvest index, and grain nutritive value (sugars, vitamin B, and Co contents) were significantly enhanced by Co in both varieties. However, the maximum performance was observed in Giza 178. [ABSTRACT FROM AUTHOR]