Evaluation of drought-tolerant rice varieties under system of rice intensification in water-scarce regions

Introduction

Since the Green Revolution, rice improvement concentrated on irrigated ecosystems, largely bypassing rainfed lowlands [1] . In India, roughly 23% of rice area remains rainfed and prone to drought, with average yields below 2.5 t/ha compared with 4-5 t/ha in irrigated systems [2] . Drought-tolerant varieties carrying QTLs such as qDTY1.1 have shown 0.8-1.2 t/ha yield advantages over susceptible checks under reproductive-stage drought [11,15] . However, their performance under SRI management which improves root growth and water productivity has not been systematically tested [3,5] . SRI involves transplanting young single seedlings at wide spacing with intermittent wetting and drying [4,6] . This research evaluated three drought-tolerant and two check varieties under SRI and conventional management with contrasting irrigation regimes.

Materials and Methods

Field experimental design

The experiment followed a split-split-plot design with three replications. Main plots were the two crop management systems (SRI and conventional). Subplots were the two irrigation regimes (full and deficit). Sub-subplots were the five rice varieties. Individual plot size was 4 m × 5 m with 1 m borders between plots to prevent lateral water movement. Total experimental area covered 0.72 ha including buffers and bunds [9] .

Seasonal variations

The 2021 wet season received 1,143 mm rainfall (June-October), close to the 30-year average of 1,180 mm but with a 22-day dry spell during August. The 2022 season was drier overall (987 mm) with a 31-day mid-season drought coinciding with panicle initiation to flowering in latetransplanted plots. Mean temperatures ranged from 24.1 to 33.8 °C across both seasons. Deficit irrigation plots received 40% less water than full irrigation during reproductive stages [8] .

Materials: Three drought-tolerant varieties (Sahbhagi Dhan, DRR Dhan 44, CR Dhan 801) and two checks (Swarna, IR 64) were obtained from ICAR-National Rice Research Institute, Cuttack. Seeds were raised in wet-bed nurseries and transplanted at 14 days (SRI) or 25 days (conventional). SRI plots received single seedlings at 25 × 25 cm; conventional plots received 2-3 seedlings at 20 × 15 cm. Fertilizer was uniform at 100:50:50 kg N:P₂O₅:K₂O/ha [7] . Methods: Grain yield was recorded at 14% moisture from a 5 m² harvest area per plot. Water use efficiency (WUE) was calculated as grain yield divided by total water applied (irrigation plus rainfall). Root depth was measured at flowering by excavating three hills per plot. Leaf water potential was recorded pre-dawn with a pressure chamber. Data were analyzed by split-split-plot ANOVA in SAS 9.4, with means by Tukey HSD at p≤0.05. Pooled analysis used both years after Bartlett's test confirmed error homogeneity [9] .

Results

Comprehensive interpretation

Sahbhagi Dhan under SRI with full irrigation produced the highest yield at 5.87 t/ha, 29.3% above Swarna and 43.5% above IR 64 under the same conditions (Table 1, Figure 1). Under deficit irrigation, Sahbhagi Dhan maintained 4.93 t/ha a 16.0% drop while Swarna fell 32.6% and IR 64 fell 34.6%. WUE peaked during panicle initiation to flowering (Figure 2), with SRI drought-tolerant combinations reaching 2.71 kg/m³ versus 1.63 for conventional checks (Table 2). Root depth under SRI deficit was 28.4 cm for Sahbhagi Dhan compared with 17.8 cm for IR 64, a 59.6% advantage that likely sustained water uptake during the mid-season drought.

Discussion

The interaction between drought-tolerant genotype and SRI was synergistic. Varieties carrying qDTY QTLs maintain grain filling under low moisture by sustaining higher leaf water potential [11,15] . SRI practices promote deeper root systems [5,10] . Combined, these mechanisms enabled Sahbhagi Dhan to access moisture at 25-30 cm during the critical reproductive stage a zone unavailable to shallow-rooted checks under conventional management [10] . The WUE advantage of SRI (38-45% over conventional) aligns with Zhao et al. [6] and Lampayan et al. [20] . Under deficit irrigation, drought-tolerant varieties maintained higher grain output per unit water, whereas checks suffered disproportionate yield collapse during reproductive drought [18] . The 31-day drought in 2022 was more severe than 2021, yet the relative advantage of drought-tolerant varieties under SRI remained stable, indicating the genotype-management interaction holds across varying drought intensities. Serraj et al. [19] similarly concluded that genetic tolerance expresses more consistently when supported by complementary management [21] .

Conclusion

Combining drought-tolerant rice with SRI produced the highest and most stable yields under both full and deficit irrigation. Sahbhagi Dhan under SRI gave 5.87 t/ha with full water and 4.93 t/ha under 40% deficit only a 16% decline versus 32-35% in checks. SRI boosted WUE by 38-45%. Root depth exceeded 27 cm in drought-tolerant SRI plots. Extension programs should promote Sahbhagi Dhan and CR Dhan 801 with SRI protocols as a practical package for droughtprone eastern Indian lowlands. Multi-season trials across agroclimatic zones would confirm these results at scale.

References

1. Pandey S, Bhandari H, Hardy B. Economic costs of drought and rice farmers coping mechanisms: A cross-country comparative analysis. Int Rice Res Inst. 2007;1-203.
2. Kumar A, Bernier J, Verulkar S, Lafitte HR, Atlin GN. Breeding for drought tolerance: Direct selection for yield, response to selection, and use of drought-tolerant donors in upland and lowland-adapted populations. Field Crops Res. 2008;107(3):221-231.
3. Uphoff N. Agroecological implications of the system of rice intensification (SRI) in Madagascar. Environ Dev Sustain. 1999;1(3):297-313.
4. Stoop WA, Uphoff N, Kassam A. A review of agricultural research issues raised by the system of rice intensification. Agric Syst. 2002;71(3):249-274.
5. Thakur AK, Rath S, Roychowdhury S, Uphoff N. Comparative performance of rice with system of rice intensification and conventional management. Paddy Water Environ. 2010;8(2):129-141.
6. Zhao L, Wu L, Li Y, Lu X, Zhu D, Uphoff N. Influence of the system of rice intensification on rice yield and nitrogen and water use efficiency. Agron J. 2009;101(6):1453-1461.
7. Verulkar SB, Mandal NP, Dwivedi JL, Singh BN, Sinha PK, Mahato RN, Dongre P, Singh ON, Bose LK, Swain P, Robin S, Chandrababu R, Senthil S, Jain A, Shashidhar HE, Hittalmani S, Vera Cruz C, Paris T, Raman A, Haefele S, Serraj R, Atlin G, Kumar A. Breeding resilient and productive genotypes adapted to drought-prone rainfed ecosystem of India. Field Crops Res. 2010;117(2):197-208.
8. Bouman BAM, Tuong TP. Field water management to save water and increase its productivity in irrigated lowland rice. Agric Water Manag. 2001;49(1):11-30.
9. Gomez KA, Gomez AA. Statistical procedures for agricultural research. John Wiley and Sons. 1984;1-680.
10. Henry A, Gowda VRP, Torres RO, McNally KL, Serraj R. Variation in root system architecture and drought response in rice: Phenotyping of the OryzaSNP panel in rainfed lowland fields. Field Crops Res. 2011;120(2):205-214.
11. Vikram P, Swamy BPM, Dixit S, Ahmed HU, Sta Cruz MT, Singh AK, Kumar A. qDTY1.1, a major QTL for rice grain yield under reproductive-stage drought stress with a consistent effect in multiple elite genetic backgrounds. BMC Genet. 2011;12:89.
12. Ceesay M, Reid WS, Fernandes ECM, Uphoff N. The effects of repeated soil wetting and drying on lowland rice yield with SRI. Int J Agric Sustain. 2006;4(1):5-14.
13. Sinha SK, Talati J. Productivity impacts of the system of rice intensification: A case analysis in West Bengal. Agric Water Manag. 2007;87(1):55-60.
14. Mishra A, Salokhe VM. Seedling characteristics and early growth of transplanted rice under different water regimes. Exp Agric. 2008;44(3):365-383.
15. Bernier J, Kumar A, Ramaiah V, Spaner D, Atlin G. A large-effect QTL for grain yield under reproductive-stage drought stress in upland rice. Crop Sci. 2007;47(2):507-516.
16. Tuong TP, Bouman BAM, Mortimer M. More rice, less water: Integrated approaches for increasing water productivity in irrigated rice-based systems in Asia. Plant Prod Sci. 2005;8(3):231-241.
17. Kijne JW, Barker R, Molden D. Water productivity in agriculture: Limits and opportunities for improvement. CABI Publishing. 2003;1-332.
18. Prasad PVV, Staggenborg SA, Ristic Z. Impacts of drought and heat stress on physiological, developmental, growth, and yield processes of crop plants. Adv Agric Syst Model. 2008;1:301-355.
19. Serraj R, McNally KL, Slamet-Loedin I, Kohli A, Haefele SM, Atlin G, Kumar A. Drought resistance improvement in rice: An integrated genetic and resource management strategy. Plant Prod Sci. 2011;14(1):1-14.
20. Lampayan RM, Rejesus RM, Singleton GR, Bouman BAM. Adoption and economics of alternate wetting and drying water management for irrigated lowland rice. Field Crops Res. 2015;170:95-108.
21. Sandhu N, Dixit S, Swamy BPM, Vikram P, Venkateshwarlu C, Catolos M, Kumar A. Positive interactions of major-effect QTLs with genetic background that enhances rice yield under drought. Sci Rep. 2018;8:1626.