Sequential submergence and drought induce yield loss in rice by affecting redox homeostasis and source-to-sink sugar transport

Rice cultivation in the rainfed ecosystems of the eastern Indo-Gangetic plain (EIGP) frequently comes across abrupt alternation of submergence and drought during the vegetative and reproductive stages, respectively, within one growing season, and this may be exaggerated with climate change. Therefore, development of combined submergence and drought tolerant rice genotypes might be a timely effort to meet the growing food demand. However, till date no study has been executed on the combination of submergence and drought stress in the field conditions of the EIGP. The present study elucidated the performance of near isogenic lines (NILs) of rice developed for the EIGP through marker assisted pyramiding of quantitative trait loci (QTL) associated with submergence (Sub1) and drought (qDTY1.1 + qDTY2.1 + qDTY3.1) in the background of the popular, high yielding Indo-Gangetic rice variety Swarna. This study included the screening of sixteen rice NILs along with the check varieties Swarna and Swarna Sub1 under cumulative submergence and drought for four consecutive rice growing years (2019–2022). Individual submergence or drought or cumulative stress caused 76, 47, and 85% respective loss in average productivity compared to that of the control conditions. However, rice NILs IR96321–558–563-B-2–1–1, IR96321–315–323-B-3–1–3, IR96321–315–294-B-1–1–1–1, and IR96321–558–209-B-6–1–1 showed outstanding cumulative stress tolerance with sustainable photosynthetic performance and membrane stability. Furthermore, these rice NILs exhibited effective reactive oxygen species scavenging mediated by enhanced antioxidant enzyme activities in source (flag-leaf) and sink (anther) tissues that contributed to conserving the source-to-sink mobilization, leading to improved pollen viability and spikelet fertility under sequential stress conditions. The study identified combined submergence-drought tolerant rice NILs along with an optimum yield level to support global food security and also represented a model crop system to establish mechanisms of multi-stress tolerance in plants.