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Understanding response of plants to drought stress is critical for developing drought tolerant genotypes with stable performance under water limiting conditions. A backcross inbred population derived in the background of a popular variety Swarna, was evaluated for yield and yield attributing traits under reproductive stage and shoot morphological traits at seedling stage under drought stress over a period of two years during 2011-2013. Selection intensity varied across seasons and years with varied level of moisture stress. Traits such as flowering (DTF), plant height (PH), spikelet fertility (SF), biomass (BM), harvest index (HI) and grain yield (GY) are drastically affected by drought across seasons. Yield reduction varied from 48.5% to 92.4% over control trials. Chlorophyll content (CC) and canopy temperature (CT) recorded higher under drought rather than control. Yield was highly associated with DTF (−0.29* to −0.76**), SF (0.32** to 0.77**), HI (0.82** to 0.97**) and CT (−0.38**). Heritability is found to be similar for grain yield under both conditions. Genotypes displaying higher SF and HI, lower CT, reduction in flowering delay and low DSI are able to produce better grain yield under drought. High yielding genotypes at reproductive stage stress also showed superior performance under stress at seedling stage. Hence, selection intensity for high yield potential under favorable conditions, drought tolerance to varied level of stress (across seasons) and screening under target population environment had the advantage of identifying stable high yielding genotypes with wider adaption suitable for drought-prone regions, which can significantly benefits the poor farmers relying on rainfed lowland rice.

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Drought is a major constraint for rainfed lowland and upland rice productivity throughout world. A backcross inbred population derived from ‘Swarna’ and ‘WAB450-I-B-P-157-2-1’ (Oryza sativa L. x O. glaberrima) was evaluated under both irrigated and lowland drought stresses for yield and yield related traits across three different seasons. Significant differences were found among all the analyzed traits. Coefficients of variation were recorded relatively high for filled grains per panicle, spikelet fertility, test weight, harvest index and grain yield and low for panicle length under both conditions during the study interval. Broad sense heritability varied from 0.28 (panicle number) to 0.83 (plant height) under stress and 0.31 (test weight) to 0.86 (plant height) under control. However, heritability estimates for grain yield and harvest index were found to be similar under both conditions. Traits such as filled grains per panicle, spikelet fertility, harvest index and grain yield recorded higher values of both heritability, as well as genetic advance under both conditions, indicating the suitability of these traits as selection criteria to derive high yielding genotypes for drought prone regions. Harvest index exhibited maximum positive direct effect on grain yield under both the conditions; in addition, filled grains per panicle, spikelet fertility and biomass had positive direct effect on grain yield under both irrigated and lowland drought stresses state. Hence, for improving the rice yield under lowland drought ecology, a genotype should posses a large number of panicles per plant, filled grains per panicle, high spikelet fertility and maintains higher biomass and harvest index.