Impact of Seedling Age and Nitrogen Application on Submergence Tolerance of Sub1 and Non-Sub1 Cultivars of Rice (Oryza sativa L.)

Flooding is an environmental stress that can affect crops at any stage, seriously affecting crop establishment leading to severe yield losses. The study was undertaken to understand the response of age of seedlings and nitrogen application on submergence tolerance of rice with Sub1 and non-Sub1 cultivars. This study assesses growth after recovery and several physiological mechanisms associated with submergence tolerance in rice. Survival, growth after recovery, allometric parameters, carbohydrate content, and photosynthesis decreased due to submergence with greater extent in younger seedlings. After desubmergence, all the cultivars experienced oxidative damage at all seedling ages and antioxidant activity was higher in tolerant cultivars. Forty-day-old seedlings had significantly higher submergence tolerance and recovery scores, assessed based on survival, re-generation ability, and growth, leading to higher yields. Higher maintenance of sugar and starch (60.9% higher) in forty-day-old seedlings was another reason for higher plant survival and lower mortality. The crop fertilized with post-flood nitrogen resulted in substantially better survival, leaf and root growth, photosynthesis, and yield, and the effect was more positive in older seedlings of Sub1 cultivars. These low-input cost-effective approaches have been a good option for enhancing submergence tolerance and yield in stress-prone areas of South-East Asia.