Scientists Stack Drought and Flood Tolerance Genes Into Beloved Rice Variety

Rice is the staple food for more than half of humanity, yet the rainfed lowlands where much of it grows are among the most unpredictable environments in agriculture. In a single season, the same field can swing from parched cracks in the soil to complete submergence under floodwater, and farmers have historically had little recourse against either extreme. Now, a team of Indian plant breeders and biotechnologists has reported a significant step toward insurance against both: they have successfully combined multiple genetic regions conferring drought tolerance with the well-known submergence-tolerance locus Sub1 in the background of Samba Mahsuri, one of India’s most widely grown and best-loved rice varieties. The work, published in the Indian Journal of Genetics and Plant Breeding, demonstrates how precision molecular breeding can equip an elite cultivar for the climate of the coming decades without sacrificing the grain quality that made it famous.

Samba Mahsuri occupies a special place in Indian agriculture. The variety, developed decades ago, is prized for its excellent cooking and eating quality, with slender, fine grains that command strong consumer preference across southern and eastern India. Its popularity, however, has always been tempered by two weaknesses. It matures late, extending the crop’s exposure to end-of-season water shortages, and it is highly sensitive to both drought and flash flooding. In the rainfed lowland agro-ecosystem, where fields depend on erratic monsoon rainfall rather than assured irrigation, these weaknesses translate into devastating yield losses in bad years. Farmers who grow Samba Mahsuri do so for its market value, but they accept a substantial risk every time they sow it.

The strategy the researchers employed is known as QTL pyramiding. Quantitative trait loci, or QTLs, are stretches of the genome that harbor genes influencing complex, quantitatively inherited traits such as yield under stress. Unlike single-gene resistances, drought tolerance is controlled by many loci of small to moderate effect, and breeding programs have identified several major-effect QTLs that reliably improve grain yield when water is scarce. Two of the most consistent are qDTY2.1 on chromosome 2 and qDTY3.2 on chromosome 3, both of which have been shown in previous studies to enhance yield under reproductive-stage drought across multiple genetic backgrounds. By combining these with the Sub1 locus, which confers remarkable tolerance to complete submergence for up to two weeks, the team aimed to build a single variety capable of withstanding the two most damaging water-related stresses of the rainfed lowlands.

The breeding material itself was elegant in design. The researchers crossed two advanced lines, each of which already carried the Sub1 submergence-tolerance locus in the Samba Mahsuri background: SM-Sub1-DTY2.1, which carries qDTY2.1 and is known as DRR Dhan 50, and SM-Sub1-DTY3.2, which carries qDTY3.2. From this cross, they generated a population of 990 F2 plants. Each plant was genotyped using simple sequence repeat markers linked to the two drought-tolerance QTLs, allowing the team to identify individuals that had inherited both genomic regions in homozygous form. Of the 990 plants screened, 62 such QTL-pyramided lines were identified and advanced to the F3 generation, each one now carrying the drought-tolerance loci from both parents alongside the Sub1 submergence-tolerance gene.

A crucial complication soon emerged. Because both donor parents had been selected for earlier maturity than the original Samba Mahsuri, the pyramided lines segregated for time to flowering and maturity. Maturity is not a trivial trait: farmers time their sowing, harvesting, and water management around it, and any new version of a mega-variety must match the photoperiod and duration expectations of the regions where it will be grown. The team therefore carefully selected only those lines showing uniform maturity, advancing them through the F4 to F6 generations until lines true-breeding for both the stacked QTLs and an acceptable maturity class were obtained. This step illustrates a lesson that runs through modern marker-assisted breeding: stacking useful genes is only half the job, and the other half is restoring the agronomic package that made the original variety successful.

Four of the resulting QTL-pyramided lines were then evaluated in detail for agronomic and physiological performance under both control and drought-stress conditions. The researchers measured a battery of traits, including grain yield, plant height, tiller number, leaf rolling, chlorophyll content, and relative water content, comparing the pyramided lines against the recurrent parent Samba Mahsuri and the single-QTL parental lines. The results were unambiguous. The pyramided lines lost significantly less grain yield under drought stress than either Samba Mahsuri or the lines carrying only one drought QTL, confirming that the two loci act additively or even synergistically when combined in the same genetic background. Physiological measurements supported the yield data, indicating that the pyramided lines maintained better plant water status and photosynthetic capacity as soil moisture declined.

The standout performer was a line designated QPL 62. This line showed the least reduction in grain yield under drought of any material tested, and it also matured 16 days earlier than Samba Mahsuri, an advantage that reduces its exposure to terminal water stress and allows earlier harvesting. Just as importantly, molecular profiling showed that QPL 62 retained more than 95 percent similarity to the Samba Mahsuri genetic background, and its grain and cooking quality characteristics remained essentially indistinguishable from those of the original variety. In other words, the breeders had inserted the drought and flood insurance policies without disrupting the qualities that farmers and consumers actually care about. This recovery of the recurrent parent genome is the central promise of marker-assisted backcrossing and pyramiding approaches, and the present study shows it can be achieved even when combining multiple stress-tolerance loci simultaneously.

The implications extend well beyond a single variety. Rainfed lowlands account for a substantial share of rice production in South and Southeast Asia, and climate projections suggest that both the frequency of mid-season droughts and the intensity of flood events will increase in the coming decades. Varieties that combine tolerance to multiple abiotic stresses are therefore a central goal of national and international breeding programs. The Sub1 locus has already been successfully introgressed into numerous popular varieties, including Swarna and Samba Mahsuri itself, producing flood-tolerant versions now grown on millions of hectares. Adding yield-enhancing drought QTLs on top of Sub1, as this study demonstrates in Samba Mahsuri, represents the logical next generation of climate-resilient rice, and the pyramiding framework can in principle be replicated in any elite cultivar for which Sub1 versions and drought-QTL donors are available.

The authors note that QPL 62 is now ready to be taken forward into multi-location QTL near-isogenic line trials, the standard pathway toward commercial release in India. If those trials confirm its performance across diverse environments, the line could eventually be notified as a climate-resilient version of Samba Mahsuri, giving farmers the same prized grain quality with dramatically reduced risk from drought and flooding. The work was supported by the Indian Council of Agricultural Research Network Project on Translational Genomics in Crop Plants and by an Anusandhan National Research Foundation JC Bose National Fellowship. As extreme weather increasingly tests the world’s rice fields, studies like this one show that the tools of genomics can convert a beloved but vulnerable variety into one that can weather the storm, and the flood, on its own genetic merits.

Subject of Research: Marker-assisted pyramiding of drought and submergence tolerance QTLs in rice variety Samba Mahsuri to develop a climate-resilient cultivar.

Article Title: Pyramiding of Multiple QTL for Drought and Submergence Tolerance for Infusing Climate-Resilience in Rice Variety Samba Mahsuri

Article References: Jain, P., Kapoor, R. T., Kumar, M., Yadav, N., Rani, M., Joshi, R., Rai, V., Bisht, D. S., Gaikwad, K., & Singh, N. K. (2026). Pyramiding of Multiple QTL for Drought and Submergence Tolerance for Infusing Climate-Resilience in Rice Variety Samba Mahsuri. Indian Journal of Genetics and Plant Breeding, 86(3), 279-291. https://doi.org/10.1007/s44489-026-00028-x

Image Credits: AI Generated

DOI: 10.1007/s44489-026-00028-x

Keywords: rice, Samba Mahsuri, QTL pyramiding, drought tolerance, submergence tolerance, qDTY2.1, qDTY3.2, Sub1, marker-assisted selection, climate resilience, molecular breeding, rainfed lowland