Breeding drought tolerant rice for shallow rainfed ecosystem of eastern India

- For vegetative-stage drought screening in the dry season, maintaining the soil water potential above −20 kPa as monitored at 30 cm depth is recommended to be able to clearly distinguish between tolerant and susceptible genotypest.
- This study identified some genotypes that were susceptible to drought in reproductive-stage drought stress but showed tolerance of vegetative-stage drought stress, indicating the distinct response of rice to drought stress at these two growth stages.
- Combining tolerance of vegetative-stage drought with tolerance of reproductive-stage drought could be accomplished by performing separate vegetative- and reproductive-stage drought stress screening trials, which in this study resulted in the identification of genotypes IR72667-16-1-B-B-3, IR78908-126-B-2-B, and IR79970-B-47-1 as tolerant of both stages of drought stress.
- The development of improved varieties with combined tolerance of drought stress at multiple growth stages will help farmers in rainfed rice-growing regions maintain stable yields across increasingly unpredictable climatic conditions.

In shallow rainfed rice agro-ecosystems, drought stress can occur at any growth stage and can cause a significant yield reduction. During recent years, some rice varieties possessing tolerance of reproductive-stage drought stress have recently been developed. Tolerance of vegetative-stage drought stress is also required to improve rice productivity in drought-prone regions. In this study, we evaluated a set of rice breeding lines for their response to a range of different types of vegetative-stage drought stress in order to propose standardized phenotyping protocols for conducting vegetative-stage drought stress screening trials and also to identify genotypes combining tolerance of vegetative- and reproductive-stage drought stress. A soil water potential threshold of −20 kPa during the vegetative stage was identified as the target for effective selection under vegetative stage with grain yield reduction of about 50% compared to irrigated control trials. Genotypes identified as showing high yield under reproductive-stage drought stress were not necessarily the genotypes showing best performance under vegetative-stage drought stress. Genotypes IR72667-16-1-B-B-3, IR78908-126-B-2-B, and IR79970-B-47-1 showed tolerance of both vegetative-stage and reproductive-stage drought stress. For most, the genotypes that were best under vegetative stage drought or even vegetative stage + reproductive stage drought were different from the genotypes that were best under reproductive stage drought. Based on the cultivar superiority measure, IR69515-6-KKN-4-UBN-4-2-1-1-1 and IR78908-126-B-1-B were the stable genotypes (indicated by low Pi) under both irrigated control and severe vegetative stress conditions, genotypes IR83614-203-B and IR78908-80-B-3-B were stable under irrigated control conditions and moderate stress, whereas IR72667-16-1-B-B-3 was stable under both moderate and severe vegetative-stage stress conditions.