Associated physiological mechanisms during reproductive stage in lines of Swarna rice (Oryza sativa) pyramided with major drought yield quantitative trait loci qDTY1.1 and qDTY3.1

Drought is a major abiotic stress that limits rice (Oryza sativa) production. Millions of hectares of rainfed lowland and upland rice in Asia are affected by drought stress yearly, which results in considerable yield reduction. Evaluation of the physiological characteristics that aid rice plants in maintaining yield under drought stress conditions may contribute to the development of potential drought-tolerant varieties. This study assessed the physiological characteristics of drought-tolerant lines with different combinations of qDTY3.1 and qDTY1.1 in the genetic background of Swarna, a popular, high-yielding but drought susceptible rice variety. Specifically, these lines were 'qDTY3.1 lines' (introgressed with qDTY3.1 alone), 'qDTY1.1 lines' (introgressed with qDTY1.1 alone), and 'pyramided lines' (introgressed with both qDTY3.1 and qDTY1.1). qDTY3.1 lines exhibited faster peduncle elongation rate, lower peduncle elongation breakpoint values, and longer final peduncle length under drought stress. qDTY1.1 lines presented more negative leaf osmotic potential and cooler canopy temperatures than Swarna that indicated better leaf hydration under drought. Pyramided lines produced higher panicle numbers, longer mean peduncle length, and higher grain yield under drought. These characteristics associated with qDTY3.1 and qDTY1.1 indicated that the plants performed better under drought stress than would be expected from the sum of the individual qDTY effects.