Incorporating Drought and Submergence Tolerance QTL in Rice (<i>Oryza sativa</i> L.)—The Effects under Reproductive Stage Drought and Vegetative Stage Submergence Stresses

Drought and submergence have been the major constraint in rice production. The present study was conducted to develop high-yielding rice lines with tolerance to drought and submergence by introgressing <i>Sub1</i> into a rice line with drought yield QTL (<i>qDTY</i>; <i>QTL</i> = quantitative trait loci) viz. <i>qDTY₃.₁</i> and <i>qDTY₁₂.₁</i> using marker-assisted breeding. We report here the effect of different combinations of <i>Sub1</i> and <i>qDTY</i> on morpho-physiological, agronomical traits and yield under reproductive stage drought stress (RS) and non-stress (NS) conditions. Lines with outstanding performance in RS and NS trials were also evaluated in vegetative stage submergence stress (VS) trial to assess the tolerance level. The QTL class analysis revealed <i>Sub1</i> + <i>qDTY₃.₁</i> as the best QTL combination affecting the measured traits in RS trial followed by <i>Sub1</i> + <i>qDTY₁₂.₁</i>. The effects of single <i>Sub1</i>, <i>qDTY₃.₁</i> and <i>qDTY₁₂.₁</i> were not as superior as when the QTLs are combined, suggesting the positive interaction of <i>Sub1</i> and <i>qDTY</i>. Best performing lines selected from the RS and NS trials recorded yield advantage up to 4453.69 kg ha⁻¹ and 6954 kg ha⁻¹ over the parents, respectively. The lines were also found having great tolerance to submergence ranging from 80% to 100%, contributed by a lower percentage of shoot elongation and reduction of chlorophyll content after 14 days of VS. These lines could provide yield sustainability to farmers in regions impacted with drought and submergence while serving as important genetic materials for future breeding programs.