Redox imbalance disrupts spikelet fertility in rice: A study under stage-specific and multi-stage drought in eastern Indo-Gangetic plain

To support the increasing food demand of the drought-prone eastern Indo-Gangetic plain (EIGP), we assessed the effects of natural drought stress on the individual (seedling stage drought; SSD, vegetative stage drought; VSD, reproductive stage drought; RSD) as well as the multiple growth stages (multi-stage drought; MSD) of twenty-four rice genotypes (n = 24) under field conditions for two consecutive rice growing seasons (2019–2020). High temperature and low rainfall during both the trial years exerted moderate to severe drought stress to the rice genotypes leading to average grain yield reduction of 43.5%, 28.9%, 59.3%, and 69.9% under SSD, VSD, RSD, and MSD conditions, respectively. The present study also revealed that drought stress caused enhanced accumulation of reactive oxygen species (ROS) in the spikelets of rice genotypes thereby, impeding the spikelet fertility. The promising rice genotypes showed an average decrease of 3.18%, 4.83%, 13.9%, and 13.06% in spikelet fertility under SSD, VSD, RSD, and MSD conditions, respectively. Identified promising rice genotypes, IR83929-B-B-291–2–1–1–2, IR93827–29–1–1–2 and IR84899-B-183–20–1–1–1 showed extreme drought tolerance and better maintained photosynthetic rate, stomatal conductance, relative water content, membrane stability index, and total chlorophyll content under drought conditions irrespective of growth stages. Following the study, drought tolerance in the tolerant rice genotypes was associated with increased antioxidant enzyme mediated efficacious ROS detoxification, which contributed in maintaining pollen viability and spikelet fertility. Overall, the study identified drought tolerant rice genotypes for EIGP and established a comprehensive understanding of the complexity and plasticity of the rice genotypes under stage-specific and cumulative drought stress.