Unveiling submergence tolerance in improved restorer lines of rice (Oryza sativa L.) seedlings at varied durations: evaluation through chlorophyll fluorescence and morphological responses

Abstract Submergence stress caused by flash floods is a major abiotic challenge that hampers plant growth and threatens sustainable crop production in the era of climate change. The rice restorer ‘KMR-3R’ plays a crucial role in hybrid rice breeding, but its susceptibility to submergence stress poses a significant limitation. To enhance its submergence tolerance, we employed marker-assisted backcross breeding to introgress the Sub1 gene from Swarna-Sub1 into KMR-3R. This study assessed the morpho-physiological responses of 13 backcross inbred lines (BILs) of KMR-3R (BC 2 F 6 ) at the 14-days-old seedling stage under two submergence durations (7- and 14-days). Prolonged submergence significantly impacted survival rates, chlorophyll fluorescence parameters (F v /F m , Y(II), ETR, qN, qP) and total chlorophyll content in both BILs and parental lines compared to the control. Shoot elongation was restricted at 14-days after submergence (DAS). Notably, seven BILs (TCP18, TCP28, MB44, TCP25, TCP15, TCP02 and TCP10) exhibited limited shoot elongation, stable PS II activity, while TCP18 and TCP15 showed highest survival percentage exceeding that of Swarna-Sub1 at 14-DAS highlighting their enhanced tolerance. These promising BILs have the potential to serve as improved restorer lines for the developing submergence-tolerant rice hybrids in flash floods prone ecosystem.