Trait Combinations That Improve Rice Yield under Drought: Sahbhagi Dhan and New Drought-Tolerant Varieties in South Asia

Drought is one of the most severe constraints reducing rice (Oryza sativa L.) yield in rainfed environments. ‘Sahbhagi Dhan’ (IR74371-70- 1-1) is a drought-tolerant rice variety that was released in India in 2010—and subsequently in Nepal as ‘Sukha Dhan 3’ and in Bangladesh as ‘BRRI Dhan 56’—and has performed well in rainfed farmers’ fields. This study was conducted to understand the physiological drought response characteristics of Sahbhagi Dhan that contribute to its increased yield under drought. Physiological characterization of Sahbhagi Dhan and other newer breeding lines was conducted across multiple seasons at one site in the Philippines and at four sites in India. Several distinct traits of Sahbhagi Dhan were observed: high emergence rates under direct-seeded germination- stage stress, a high proportion of total root length as lateral roots in some seasons, high harvest index under drought, and high yield stability across wet seasons. However, some unfavorable responses of Sahbhagi Dhan were observed: impaired growth when sown during seasons with early-stage cold temperatures or low solar radiation, resulting in relatively low yield stability across dry seasons. These results point to the importance of combining multiple traits for yield stability across drought-prone environments. Some of the newly developed breeding lines showed even greater yield stability than Sahbhagi Dhan, reflecting the effectiveness of ongoing improvement through direct selection for grain yield under drought that has resulted in advantageous combinations of physiological traits to increase yield in farmers’ fields.

干旱是雨养环境下限制水稻（Oryza sativa L.）产量的最严重胁迫因子之一。‘Sahbhagi Dhan’（IR74371-70-1-1）是一种耐旱水稻品种，于2010年在印度审定推广，后续分别以‘Sukha Dhan 3’之名在尼泊尔登记推广、以‘BRRI Dhan 56’之名在孟加拉国登记推广，并在雨养农户田块中表现优异。本研究旨在解析Sahbhagi Dhan在干旱胁迫下提升产量的生理干旱响应特性。研究团队在菲律宾1个试验点、印度4个试验点的多季种植环境中，对Sahbhagi Dhan及其他新型育种株系开展了生理特性鉴定。研究观察到Sahbhagi Dhan具备多项独特性状：直播发芽期胁迫下的高出苗率、部分季别下侧根占总根长比例较高、干旱胁迫下的高收获指数，以及湿季环境下的高产量稳定性。但同时也发现Sahbhagi Dhan存在部分不利响应：在早期低温或光照不足的季别播种时，其生长会受到抑制，进而导致旱季环境下的产量稳定性相对较低。上述研究结果表明，在干旱频发环境中实现产量稳定性，需结合多项优良性状。部分新培育的育种株系在产量稳定性上优于Sahbhagi Dhan，这体现了通过直接针对干旱胁迫下籽粒产量进行选择的持续改良策略的有效性——该策略已筛选出具备优势生理性状组合的株系，可提升农户田块的水稻产量。