Associated physiological mechanisms of major drought yield quantitative trait loci during reproductive stage in Swarna pyramided rice lines

Drought is one of the major abiotic stresses globally which hampers rice yield production. With this, evaluation of physiological mechanistic effects of major drought-yield quantitative trait loci is of immense importance to identify different physiological characteristics which can aid rice plants to tolerate and withstand drought stress conditions. This study assessed the individual effect and interaction of qDTY sub 3.1 and qDTY sub 1.1 through pyramiding in the genetic background of Swarna. A total of 77 rice genotypes were included encompassing 16 cropping seasons and 16 parameters were measured in various seasons. Line introgressed with qDTY sub 3.1 exhibited faster peduncle elongation as shown by shorter breakpoint values in the growth curve under drought stress. Also, qDTY sub 3.1 lines revealed lesser reduction percentage in its peduncle length as compared to Swarna. Lines with qDTY sub 1.1 consistently presented more negative leaf osmotic potential and cooler canopy temperature than Swarna which indicated higher leaf hydration under drought. These physiological mechanisms contributed in the ability of the plants to further continue their growth and development even under stress condition. Pyramided lines can develop higher root length density in medium-deep layers of the soil which helped the plants to uptake greater amount of water. These genotypes can also contribute greater amount of photosynthates to developing grains due to the production of longer peduncles in shorter period of time as shown by lower breakpoint value of the genotypes. Lastly pyramided lines also revealed the highest panicle number among all the QTL groups when exposed to reproductive stage drought stress. These agronomical and physiological characteristics associated with pyramiding qDTY sub 3.1 and qDTY sub 1.1 aided the plants to produce highest grain yield across different cropping seasons under drought stress. Generally, the study found that different physiological mechanisms related with qDTY sub 3.1 and qDTY sub 1.1 can be further improved through pyramiding due to synergistic effects. The positive interaction of these two major-effect drought yield QTL in Swarna background can help in the enhancement of rice yield production under drought stress conditions.