Biochemical, Anatomical, Genetic, and Yield Assessment of Seven Rice Genotypes (<i>Oryza sativa</i> L.) Subjected to Drought Stress

Drought stress is one of the main environmental challenges that dramatically reduce global rice production within several agricultural ecosystems. Breeding drought-tolerant rice genotypes is an important sustainable strategy to overcome this constraint. In this work, drought tolerance levels were assessed according to biochemical, anatomical, and molecular aspects, which led to selecting three promising crosses (Sakha 107 × Sakha super 300, Sakha 107 × M206, and Sakha 107 × Sakha 108) that were compared with their parents as controls. The antioxidant capabilities of the chosen potential crosses, such as the ascorbate peroxidase activity (APX), superoxide dismutase activity (SOD), catalase activity (CAT), and total phenolics, were significantly higher compared with their parents under drought stress. Moreover, the promising selected crosses could accumulate greater proline and chlorophyll contents. The potential superiority of the three selected rice crosses was anatomically represented throughout cross-sections of roots, stems, and leaves, which recorded higher values of cross-section diameter, epidermal thickness, cortex thickness, mesophyll thickness, and bundle sheath thickness as well as a broader range of xylem vessel diameters than their parents under a water deficit. The observed superiority of the antioxidant activities in the overall drought-tolerance mechanisms and anatomical characteristics reflected their protective role in the adaptation process under water stress. Molecular analyses using inter-simple sequence repeat (ISSR) markers suggested two promising crosses (Sakha 107 × Sakha super 300 and Sakha 107 × M206) to be the most suitable crosses for saving water. They had the highest similarity values and were grouped in a distinct cluster. The relative gene expression of <i>OsACS2</i>, <i>OsCML31</i>, <i>OsCYP94C2a</i>, and <i>OsSRO1c</i> was significantly elevated in the two selected drought-tolerant rice genotypes (Sakha 107 × Sakha super 300 and Sakha 107 × M206).