Abstract

The increasing concentration of greenhouse gases (GHGs) in Earth’s atmosphere leads to global warming, which further causes a series of climate changes and does great harm to both human society and natural ecosystems. Agricultural GHG emissions, mainly in the form of methane (CH4) and nitrous oxide (N2O), are a significant source of GHGs, accounting for ∼14% total global GHGs (Zhang et al., 2022Zhang X. Sun H. Bi J. Yang B. Zhang J. Wang C. Zhou S. Estimate greenhouse gas emissions from water-saving and drought-resistance rice paddies by deNitrification-deComposition model.Clean. Technol. Environ. Policy. 2022; 24: 161-171Crossref Scopus (2) Google Scholar). One major source of agricultural GHGs is CH4 emissions from rice paddies, which is responsible for ∼10%–12% of human-induced CH4 emissions (van Groenigen et al., 2013van Groenigen K.J. van Kessel C. Hungate B.A. Increased greenhouse-gas intensity of rice production under future atmospheric conditions.Nat. Clim. Chang. 2013; 3: 288-291Crossref Scopus (121) Google Scholar) and contributes ∼2.40% to the enhanced global warming effect (Zhang et al., 2022Zhang X. Sun H. Bi J. Yang B. Zhang J. Wang C. Zhou S. Estimate greenhouse gas emissions from water-saving and drought-resistance rice paddies by deNitrification-deComposition model.Clean. Technol. Environ. Policy. 2022; 24: 161-171Crossref Scopus (2) Google Scholar). The global warming potential of GHGs emissions from rice systems is roughly four times higher than either wheat or maize (Linquist et al., 2012Linquist B. Groenigen K.J. Adviento-Borbe M.A. Pittelkow C. Kessel C. An agronomic assessment of greenhouse gas emissions from major cereal crops.Glob. Change Biol. 2012; 18: 194-209Crossref Scopus (424) Google Scholar). Moreover, we must acknowledge that global warming increases the GHG emissions from rice paddies, while GHG emissions promote global warming, ultimately causing rice-yield losses and greatly threatening global food security (van Groenigen et al., 2013van Groenigen K.J. van Kessel C. Hungate B.A. Increased greenhouse-gas intensity of rice production under future atmospheric conditions.Nat. Clim. Chang. 2013; 3: 288-291Crossref Scopus (121) Google Scholar). Therefore, GHG emissions from rice paddies are an unprecedented major concern in the context of food security, which is drawing global attention. A major challenge in the development of sustainable rice is how to break the vicious cycle of GHG emissions and global warming in rice production. In China, the goal of carbon neutrality in rice production, which means zero net CO2 emission from rice field, has been proposed.There is great potential to mitigate global warming by reducing agricultural GHG emissions from rice paddies. The CH4 released from rice paddies is produced mainly by methanogens through anaerobic decomposition of organic matter. Water-logged paddy fields, which account for ∼50% of total agricultural water usage, provide an ideal anaerobic condition for CH4 production. Therefore, freeing rice cultivation from logged water is the most promising strategy to reduce CH4 emissions (Li et al., 2006Li C. Salas W. DeAngelo B. Rose S. Assessing alternatives for mitigating net greenhouse gas emissions and increasing yields from rice production in China over the next twenty years.J. Environ. Qual. 2006; 35: 1554-1565Crossref PubMed Scopus (153) Google Scholar), which is named the “blue revolution.” Water saving in rice production can be achieved by water management and germplasm innovation. Great efforts have been made in the field of water management. For example, many water-saving cultivation methods (e.g., midseason drainage, intermittent irrigation, and drip irrigation) have been developed to reduce water usage (Li et al., 2006Li C. Salas W. DeAngelo B. Rose S. Assessing alternatives for mitigating net greenhouse gas emissions and increasing yields from rice production in China over the next twenty years.J. Environ. Qual. 2006; 35: 1554-1565Crossref PubMed Scopus (153) Google Scholar; He et al., 2013He H. Ma F. Yang R. Chen L. Jia B. Cui J. Fan H. Wang X. Li L. Rice performance and water use efficiency under plastic mulching with drip irrigation.PLoS One. 2013; 8: e83103Crossref PubMed Scopus (46) Google Scholar). However, the water-saving cultivation greatly changes the field microecology (e.g., soil-water, soil-nutrient, soil-pH, and soil-oxygen conditions). Thus, morphological, physiological, and biochemical adjustments are required for rice cultivars so that they can well adapt to water-saving cultivations.Can elite paddy rice meet such challenges of food security under carbon neutrality by the water-saving cultivation? The long history of breeding for higher yield during the domestication of paddy rice leads to its higher productivity. However, the high-yielding relies on sufficient water supply, large consumption of fertilizers, frequent applications of pesticides, and refined field management. Paddy rice has lost the ability to adapt to the rainfed dry-farming system, which means they cannot reach their yield potential under water-saving cultivation (He et al., 2013He H. Ma F. Yang R. Chen L. Jia B. Cui J. Fan H. Wang X. Li L. Rice performance and water use efficiency under plastic mulching with drip irrigation.PLoS One. 2013; 8: e83103Crossref PubMed Scopus (46) Google Scholar) due to low water-use efficiency (WUE; calculated as the grain yield per unit of water used) and poor drought resistance. Therefore, developing new rice varieties well adapted to the water-saving cultivation is necessary to achieve a balance between high yield and low GHG emissions.To develop a new category of rice cultivars well suited for the coming revolution of rice production for food security under carbon neutrality, we shall pay attention to an ancient rice germplasm, upland rice. Upland rice has been domesticated and adapted to the rainfed and resource-limited upland agroecosystems for thousands of years (Bernier et al., 2008Bernier J. Atlin G.N. Serraj R. Kumar A. Spaner D. Breeding upland rice for drought resistance.J. Sci. Food Agric. 2008; 88: 927-939Crossref Scopus (210) Google Scholar). The upland rice agroecosystem, which is characterized as dry farming, irrigation free, and resource and labor saving, is the most environment-friendly rice agroecosystem in terms of GHG emissions (Li et al., 2006Li C. Salas W. DeAngelo B. Rose S. Assessing alternatives for mitigating net greenhouse gas emissions and increasing yields from rice production in China over the next twenty years.J. Environ. Qual. 2006; 35: 1554-1565Crossref PubMed Scopus (153) Google Scholar). Farmers must balance productivity and drought resistance of upland rice to obtain a satisfactory but stable yield in either rain-sufficient or drought years. Therefore, upland rice has underwent bi-directional selection during its domestication and accumulated abundant genetic resources of water-saving characteristics and drought resistance (Xia et al., 2019Xia H. Luo Z. Xiong J. Ma X. Lou Q. Wei H. Qiu J. Yang H. Liu G. Fan L. et al.Bi-directional selection in upland rice leads to its adaptive differentiation from lowland rice in drought resistance and productivity.Mol. Plant. 2019; 12: 170-184Abstract Full Text Full Text PDF PubMed Scopus (31) Google Scholar). However, the planting area of traditional upland rice has been disappearing due to its poor productivity.Inspired by the story of upland rice domestication and building on the foundation of advances in paddy rice development, scientists in China have successfully developed water-saving and drought-resistance rice (WDR) by reviving genetic resources from the ancient and disappearing upland rice in elite paddy rice through conventional breeding (Luo et al., 2019Luo L. Mei H. Yu X. Xia H. Chen L. Liu H. Zhang A. Xu K. Wei H. Liu G. et al.Water-saving and drought-resistance rice: from the concept to practice and theory.Mol. Breed. 2019; 39: 145Crossref Scopus (19) Google Scholar). WDR possesses a high WUE and good drought resistance from upland rice, making it suitable for aerobic cultivation with less water and fertilizer (Luo et al., 2019Luo L. Mei H. Yu X. Xia H. Chen L. Liu H. Zhang A. Xu K. Wei H. Liu G. et al.Water-saving and drought-resistance rice: from the concept to practice and theory.Mol. Breed. 2019; 39: 145Crossref Scopus (19) Google Scholar). It is bred from the progenies of hybridization between the elite paddy rice and drought-resistant upland rice, followed by the bi-directional selections between drought resistance and yield potential for multiple seasons. With this breeding and selection strategy, we have successfully integrated WUE, drought avoidance, drought tolerance, high yield potential, and good quality in the WDR (Luo et al., 2019Luo L. Mei H. Yu X. Xia H. Chen L. Liu H. Zhang A. Xu K. Wei H. Liu G. et al.Water-saving and drought-resistance rice: from the concept to practice and theory.Mol. Breed. 2019; 39: 145Crossref Scopus (19) Google Scholar). The success of WDR breeding indicates that even a complex trait, such as drought resistance, can be improved through conventional breeding methods once appropriate strategies are applied. WDR breeding overcomes the shortages of genetic modification through the manipulation of a single drought-resistant gene, which has not yet fulfilled the expected yield benefits in field production. The development of WDR also promotes research on rice drought resistance, during which the genetic basis of drought resistance is disclosed and many drought-resistant genes have been identified (Luo et al., 2019Luo L. Mei H. Yu X. Xia H. Chen L. Liu H. Zhang A. Xu K. Wei H. Liu G. et al.Water-saving and drought-resistance rice: from the concept to practice and theory.Mol. Breed. 2019; 39: 145Crossref Scopus (19) Google Scholar). The enhancement of drought resistance in WDR results from a systematic introduction of a network compromised of many interacted drought-resistant genes rather than a single gene (Luo et al., 2019Luo L. Mei H. Yu X. Xia H. Chen L. Liu H. Zhang A. Xu K. Wei H. Liu G. et al.Water-saving and drought-resistance rice: from the concept to practice and theory.Mol. Breed. 2019; 39: 145Crossref Scopus (19) Google Scholar). For example, the introduction of the beneficial alleles of several key genes from upland rice, such as transcription factors, has likely contributed to WDR adapting to dry-farming systems (Wei et al., 2016Wei H. Feng F. Lou Q. Xia H. Ma X. Liu Y. Xu K. Yu X. Mei H. Luo L. Genetic determination of the enhanced drought resistance of rice maintainer HuHan2B by pedigree breeding.Sci. Rep. 2016; 6: 37302Crossref PubMed Scopus (6) Google Scholar). Another case is the hybrid WDR variety Hanyou73, which pyramids drought avoidance from the male-sterile line (Huhan7A) and drought tolerance from the restore line (Hanhui3) (Supplemental Figure 1A and 1B). Drought avoidance via well-developed roots ensures that Hanyou73 absorbs more water from deeper soil layers, while drought tolerance ensures it a good survival from a severe drought. In addition, Huhan7A and Hanhui3 both have upland pedigrees (Supplemental Figure 1C), and Hanyou73 therefore possesses more upland genetic components than the elite paddy hybrids (Supplemental Table 1; Supplemental Figure 1D and 1E), which potentially contributes its good drought resistance. With the increasing knowledge in the molecular basis of WDR breeding, we can improve the procedure of WDR breeding by molecular designing.In the last two decades, 22 WDR varieties have been developed and granted national and/or local certifications after rigorous field tests (Luo et al., 2019Luo L. Mei H. Yu X. Xia H. Chen L. Liu H. Zhang A. Xu K. Wei H. Liu G. et al.Water-saving and drought-resistance rice: from the concept to practice and theory.Mol. Breed. 2019; 39: 145Crossref Scopus (19) Google Scholar), which covers more than two-thirds of the provinces in China (Figure 1A ). WDR varieties are equivalent to elite paddy rice in terms of yield and quality but also possess high WUE and good drought resistance (Luo et al., 2019Luo L. Mei H. Yu X. Xia H. Chen L. Liu H. Zhang A. Xu K. Wei H. Liu G. et al.Water-saving and drought-resistance rice: from the concept to practice and theory.Mol. Breed. 2019; 39: 145Crossref Scopus (19) Google Scholar). For example, the WUE of WDR ranges from 7.32 to 7.69 (kg∗ha−1∗mm rainfall−1), while that of elite paddy rice ranges from 5.27 to 6.99 (kg∗ha−1∗mm rainfall−1) in drip-irrigated fields (Modinat et al., 2014Modinat A.A. Liu Z.C. Vered E. Zhou L.G. Kong D.Y. Qin J.Y. Ma R.F. Yu X.Q. Liu G.L. Chen L. et al.Agronomic and ecological evaluation on growing water-saving and drought-resistant rice (Oryza sativa L.) through drip irrigation.J. Agric. Sci. 2014; 6: 110-119Google Scholar). WDR varieties, such as Hanyou73 and Huhan3, can save >40% water usage without apparent yield penalty (Modinat et al., 2014Modinat A.A. Liu Z.C. Vered E. Zhou L.G. Kong D.Y. Qin J.Y. Ma R.F. Yu X.Q. Liu G.L. Chen L. et al.Agronomic and ecological evaluation on growing water-saving and drought-resistant rice (Oryza sativa L.) through drip irrigation.J. Agric. Sci. 2014; 6: 110-119Google Scholar; Bi et al., 2019Bi J.G. Tan J.S. Zhang A.N. et al.Effects of irrigation amount on yield and water use efficiency of water-saving and drought-resistance rice (WDR).Acta Agriculturae Shanghai. 2019; 35: 7-10Google Scholar), thereby shifting irrigated paddies to aerobic conditions. WDR also performs well in rainfed fields without irrigation in many experimental sites (Figure 1D; Supplemental Table 2). The annual planting area of WDR has been expanded to ∼130 000 hectares in the Yangtze River Delta area. In addition, the WDR can improve the ability of phosphorus uptake through the organic acid metabolism in roots, which contributes to its high yield in aerobic cultivation (Bi et al., 2021Bi J. Hou D. Zhang X. Tan J. Bi Q. Zhang K. Liu Y. Wang F. Zhang A. Chen L. et al.A novel water-saving and drought-resistance rice variety promotes phosphorus absorption through root secreting organic acid compounds to stabilize yield under water-saving condition.J. Clean. Prod. 2021; 315: 127992Crossref Scopus (6) Google Scholar).WDR can be directly seeded and planted like wheat. It has been adopted in non-flooding dry fields with simplified cultivation to replace many low-beneficial dry-land crops by local farmers in China (Figure 1C). WDR performs well in newly constructed terraced fields among mountain areas or in forested regions (Figure 1C). Farmers can obtain a satisfactory yield (∼9.0 tons per hectare) from WDR under diverse water-saving cultivation modes (Figure 1C) and experience extra benefits from the saved resources and labor (Zhou et al., 2019Zhou Z. Cao J.T. Yu M.L. Zhang L.X. Analysis on the promotion and planting situation of water-saving and drought-resistant rice in Lixin county and shou county of Anhui province.Crop Res. 2019; 33: 62-65Google Scholar). Moreover, in cooperation with the International Rice Research Institute, funded by the Bill and Melinda Gates Foundation and the “green super rice (GSR)” project, WDR has been tested in many African and Asian developing countries (Figure 1B). It exhibits good performance in terms of its high and stable yield under aerobic cultivation, which is earning it an excellent reputation worldwide.Besides the equivalent yield to the elite paddy rice, planting WDR following rainfed dry farming has great environmental benefits by reducing GHG emissions without apparent yield loss (Zhang et al., 2021Zhang X. Zhou S. Bi J. Sun H. Wang C. Zhang J. Drought-resistance rice variety with water-saving management reduces greenhouse gas emissions from paddies while maintaining rice yields.Agric. Ecosyst. Environ. 2021; 320: 107592Crossref Scopus (9) Google Scholar, Zhang et al., 2022Zhang X. Sun H. Bi J. Yang B. Zhang J. Wang C. Zhou S. Estimate greenhouse gas emissions from water-saving and drought-resistance rice paddies by deNitrification-deComposition model.Clean. Technol. Environ. Policy. 2022; 24: 161-171Crossref Scopus (2) Google Scholar). In a recent 2-year field experiment (2019–2020), the cultivation of Hanyou73 in aerobic cultivations reduced CH4 emissions by 97.2% (90.71%–99.69%) in Anhui Province compared with common rice varieties with flooding cultivation (Figure 1E; Supplemental Table 3). Given the rapid development and commercialization of WDR, we can optimize the planting area of ∼670 000 hectares in China over the next 5 years, which has been projected in a current program for the high-quality development of seed industry in Shanghai. This means an annual reduction of 156 100 tons of CH4 emissions (∼4 370 000 tons of carbon dioxide equivalent) from rice paddies by replacement with WDR in total (Supplemental methods). Once the reduced carbon dioxide equivalent by WDR cultivation can be exchanged in the market, it can provide an extra benefit of up to $43.7 million for farmers annually (Supplemental methods).In the upcoming era of sustainable agriculture, the yield-prior strategy, in which how to obtain a higher yield is the first consideration in rice breeding, should be rebuilt with environment-friendly considerations. This requires great progress in crop germplasm innovation to produce resource- and labor-saving varieties and advances in simplified cultivation technologies. As a part of GSR (Luo et al., 2019Luo L. Mei H. Yu X. Xia H. Chen L. Liu H. Zhang A. Xu K. Wei H. Liu G. et al.Water-saving and drought-resistance rice: from the concept to practice and theory.Mol. Breed. 2019; 39: 145Crossref Scopus (19) Google Scholar; Yu et al., 2022Yu S. Ali J. Zhou S. Ren G. Xie H. Xu J. Yu X. Zhou F. Peng S. Ma L. et al.From Green Super Rice to green agriculture: reaping the promise of functional genomics research.Mol. Plant. 2022; 15: 9-26Abstract Full Text Full Text PDF PubMed Scopus (10) Google Scholar), WDR is bred through conventional methods by applying recurrent selections under diverse environments to improve its ability to adapt to changing environments (Luo et al., 2019Luo L. Mei H. Yu X. Xia H. Chen L. Liu H. Zhang A. Xu K. Wei H. Liu G. et al.Water-saving and drought-resistance rice: from the concept to practice and theory.Mol. Breed. 2019; 39: 145Crossref Scopus (19) Google Scholar). WDR is triggering the rice blue revolution in China, which frees rice cultivation from irrigation, labor-intensive practices, and GHG emissions. The GSR variety and its environment-friendly cultivation, as represented by WDR, will replace the conventional cultivation of paddy rice with a rebuilt balance between productivity and GHG emissions. This innovation in rice germplasm can make significant contributions to the food security and mitigation of global warming. However, there are still many scientific questions underlying the research and development of WDR. Further studies on the genetic basis of rice adaptation to dry-field cultivation and on genetic resources contributing to WUE and drought resistance in upland rice might be essential. Once we have more knowledge about these aspects, new molecular design breeding strategies may be developed and joint efforts from the scientists, breeders, farmers, and policy-makers that adopt new strategies would help achieve the sustainable rice production with fewer resources and GHG emissions in the future.FundingThis work is funded by the Shanghai Agriculture Applied Technology Development Program ( T20210104 and G2016060301 ), the National Key Research and Development Program of China ( 2018YFE0106200 ), and the Shanghai Natural Science Foundation ( 20ZR1449300 ).Author contributionsL.L., H.X., X.Z., and Y.L. wrote this manuscript. H.X., L.L., X.Z., Y.L., J.B., X.M., A.Z., H.L., L.C., H.G., K.X., H.W., G.L., F.W., Q.L., F.F., L.Z., S.C, M.Y., Z.L., T.L., M.L., H.M., X.Y., S.Z., and L.W. provided the data mentioned in this manuscript or contribute to the development of water-saving and drought-resistant rice. The increasing concentration of greenhouse gases (GHGs) in Earth’s atmosphere leads to global warming, which further causes a series of climate changes and does great harm to both human society and natural ecosystems. Agricultural GHG emissions, mainly in the form of methane (CH4) and nitrous oxide (N2O), are a significant source of GHGs, accounting for ∼14% total global GHGs (Zhang et al., 2022Zhang X. Sun H. Bi J. Yang B. Zhang J. Wang C. Zhou S. Estimate greenhouse gas emissions from water-saving and drought-resistance rice paddies by deNitrification-deComposition model.Clean. Technol. Environ. Policy. 2022; 24: 161-171Crossref Scopus (2) Google Scholar). One major source of agricultural GHGs is CH4 emissions from rice paddies, which is responsible for ∼10%–12% of human-induced CH4 emissions (van Groenigen et al., 2013van Groenigen K.J. van Kessel C. Hungate B.A. Increased greenhouse-gas intensity of rice production under future atmospheric conditions.Nat. Clim. Chang. 2013; 3: 288-291Crossref Scopus (121) Google Scholar) and contributes ∼2.40% to the enhanced global warming effect (Zhang et al., 2022Zhang X. Sun H. Bi J. Yang B. Zhang J. Wang C. Zhou S. Estimate greenhouse gas emissions from water-saving and drought-resistance rice paddies by deNitrification-deComposition model.Clean. Technol. Environ. Policy. 2022; 24: 161-171Crossref Scopus (2) Google Scholar). The global warming potential of GHGs emissions from rice systems is roughly four times higher than either wheat or maize (Linquist et al., 2012Linquist B. Groenigen K.J. Adviento-Borbe M.A. Pittelkow C. Kessel C. An agronomic assessment of greenhouse gas emissions from major cereal crops.Glob. Change Biol. 2012; 18: 194-209Crossref Scopus (424) Google Scholar). Moreover, we must acknowledge that global warming increases the GHG emissions from rice paddies, while GHG emissions promote global warming, ultimately causing rice-yield losses and greatly threatening global food security (van Groenigen et al., 2013van Groenigen K.J. van Kessel C. Hungate B.A. Increased greenhouse-gas intensity of rice production under future atmospheric conditions.Nat. Clim. Chang. 2013; 3: 288-291Crossref Scopus (121) Google Scholar). Therefore, GHG emissions from rice paddies are an unprecedented major concern in the context of food security, which is drawing global attention. A major challenge in the development of sustainable rice is how to break the vicious cycle of GHG emissions and global warming in rice production. In China, the goal of carbon neutrality in rice production, which means zero net CO2 emission from rice field, has been proposed. There is great potential to mitigate global warming by reducing agricultural GHG emissions from rice paddies. The CH4 released from rice paddies is produced mainly by methanogens through anaerobic decomposition of organic matter. Water-logged paddy fields, which account for ∼50% of total agricultural water usage, provide an ideal anaerobic condition for CH4 production. Therefore, freeing rice cultivation from logged water is the most promising strategy to reduce CH4 emissions (Li et al., 2006Li C. Salas W. DeAngelo B. Rose S. Assessing alternatives for mitigating net greenhouse gas emissions and increasing yields from rice production in China over the next twenty years.J. Environ. Qual. 2006; 35: 1554-1565Crossref PubMed Scopus (153) Google Scholar), which is named the “blue revolution.” Water saving in rice production can be achieved by water management and germplasm innovation. Great efforts have been made in the field of water management. For example, many water-saving cultivation methods (e.g., midseason drainage, intermittent irrigation, and drip irrigation) have been developed to reduce water usage (Li et al., 2006Li C. Salas W. DeAngelo B. Rose S. Assessing alternatives for mitigating net greenhouse gas emissions and increasing yields from rice production in China over the next twenty years.J. Environ. Qual. 2006; 35: 1554-1565Crossref PubMed Scopus (153) Google Scholar; He et al., 2013He H. Ma F. Yang R. Chen L. Jia B. Cui J. Fan H. Wang X. Li L. Rice performance and water use efficiency under plastic mulching with drip irrigation.PLoS One. 2013; 8: e83103Crossref PubMed Scopus (46) Google Scholar). However, the water-saving cultivation greatly changes the field microecology (e.g., soil-water, soil-nutrient, soil-pH, and soil-oxygen conditions). Thus, morphological, physiological, and biochemical adjustments are required for rice cultivars so that they can well adapt to water-saving cultivations. Can elite paddy rice meet such challenges of food security under carbon neutrality by the water-saving cultivation? The long history of breeding for higher yield during the domestication of paddy rice leads to its higher productivity. However, the high-yielding relies on sufficient water supply, large consumption of fertilizers, frequent applications of pesticides, and refined field management. Paddy rice has lost the ability to adapt to the rainfed dry-farming system, which means they cannot reach their yield potential under water-saving cultivation (He et al., 2013He H. Ma F. Yang R. Chen L. Jia B. Cui J. Fan H. Wang X. Li L. Rice performance and water use efficiency under plastic mulching with drip irrigation.PLoS One. 2013; 8: e83103Crossref PubMed Scopus (46) Google Scholar) due to low water-use efficiency (WUE; calculated as the grain yield per unit of water used) and poor drought resistance. Therefore, developing new rice varieties well adapted to the water-saving cultivation is necessary to achieve a balance between high yield and low GHG emissions. To develop a new category of rice cultivars well suited for the coming revolution of rice production for food security under carbon neutrality, we shall pay attention to an ancient rice germplasm, upland rice. Upland rice has been domesticated and adapted to the rainfed and resource-limited upland agroecosystems for thousands of years (Bernier et al., 2008Bernier J. Atlin G.N. Serraj R. Kumar A. Spaner D. Breeding upland rice for drought resistance.J. Sci. Food Agric. 2008; 88: 927-939Crossref Scopus (210) Google Scholar). The upland rice agroecosystem, which is characterized as dry farming, irrigation free, and resource and labor saving, is the most environment-friendly rice agroecosystem in terms of GHG emissions (Li et al., 2006Li C. Salas W. DeAngelo B. Rose S. Assessing alternatives for mitigating net greenhouse gas emissions and increasing yields from rice production in China over the next twenty years.J. Environ. Qual. 2006; 35: 1554-1565Crossref PubMed Scopus (153) Google Scholar). Farmers must balance productivity and drought resistance of upland rice to obtain a satisfactory but stable yield in either rain-sufficient or drought years. Therefore, upland rice has underwent bi-directional selection during its domestication and accumulated abundant genetic resources of water-saving characteristics and drought resistance (Xia et al., 2019Xia H. Luo Z. Xiong J. Ma X. Lou Q. Wei H. Qiu J. Yang H. Liu G. Fan L. et al.Bi-directional selection in upland rice leads to its adaptive differentiation from lowland rice in drought resistance and productivity.Mol. Plant. 2019; 12: 170-184Abstract Full Text Full Text PDF PubMed Scopus (31) Google Scholar). However, the planting area of traditional upland rice has been disappearing due to its poor productivity. Inspired by the story of upland rice domestication and building on the foundation of advances in paddy rice development, scientists in China have successfully developed water-saving and drought-resistance rice (WDR) by reviving genetic resources from the ancient and disappearing upland rice in elite paddy rice through conventional breeding (Luo et al., 2019Luo L. Mei H. Yu X. Xia H. Chen L. Liu H. Zhang A. Xu K. Wei H. Liu G. et al.Water-saving and drought-resistance rice: from the concept to practice and theory.Mol. Breed. 2019; 39: 145Crossref Scopus (19) Google Scholar). WDR possesses a high WUE and good drought resistance from upland rice, making it suitable for aerobic cultivation with less water and fertilizer (Luo et al., 2019Luo L. Mei H. Yu X. Xia H. Chen L. Liu H. Zhang A. Xu K. Wei H. Liu G. et al.Water-saving and drought-resistance rice: from the concept to practice and theory.Mol. Breed. 2019; 39: 145Crossref Scopus (19) Google Scholar). It is bred from the progenies of hybridization between the elite paddy rice and drought-resistant upland rice, followed by the bi-directional selections between drought resistance and yield potential for multiple seasons. With this breeding and selection strategy, we have successfully integrated WUE, drought avoidance, drought tolerance, high yield potential, and good quality in the WDR (Luo et al., 2019Luo L. Mei H. Yu X. Xia H. Chen L. Liu H. Zhang A. Xu K. Wei H. Liu G. et al.Water-saving and drought-resistance rice: from the concept to practice and theory.Mol. Breed. 2019; 39: 145Crossref Scopus (19) Google Scholar). The success of WDR breeding indicates that even a complex trait, such as drought resistance, can be improved through conventional breeding methods once appropriate strategies are applied. WDR breeding overcomes the shortages of genetic modification through the manipulation of a single drought-resistant gene, which has not yet fulfilled the expected yield benefits in field production. The development of WDR also promotes research on rice drought resistance, during which the genetic basis of drought resistance is disclosed and many drought-resistant genes have been identified (Luo et al., 2019Luo L. Mei H. Yu X. Xia H. Chen L. Liu H. Zhang A. Xu K. Wei H. Liu G. et al.Water-saving and drought-resistance rice: from the concept to practice and theory.Mol. Breed. 2019; 39: 145Crossref Scopus (19) Google Scholar). The enhancement of drought resistance in WDR results from a systematic introduction of a network compromised of many interacted drought-resistant genes rather than a single gene (Luo et al., 2019Luo L. Mei H. Yu X. Xia H. Chen L. Liu H. Zhang A. Xu K. Wei H. Liu G. et al.Water-saving and drought-resistance rice: from the concept to practice and theory.Mol. Breed. 2019; 39: 145Crossref Scopus (19) Google Scholar). For example, the introduction of the beneficial alleles of several key genes from upland rice, such as transcription factors, has likely contributed to WDR adapting to dry-farming systems (Wei et al., 2016Wei H. Feng F. Lou Q. Xia H. Ma X. Liu Y. Xu K. Yu X. Mei H. Luo L. Genetic determination of the enhanced drought resistance of rice maintainer HuHan2B by pedigree breeding.Sci. Rep. 2016; 6: 37302Crossref PubMed Scopus (6) Google Scholar). Another case is the hybrid WDR variety Hanyou73, which pyramids drought avoidance from the male-sterile line (Huhan7A) and drought tolerance from the restore line (Hanhui3) (Supplemental Figure 1A and 1B). Drought avoidance via well-developed roots ensures that Hanyou73 absorbs more water from deeper soil layers, while drought tolerance ensures it a good survival from a severe drought. In addition, Huhan7A and Hanhui3 both have upland pedigrees (Supplemental Figure 1C), and Hanyou73 therefore possesses more upland genetic components than the elite paddy hybrids (Supplemental Table 1; Supplemental Figure 1D and 1E), which potentially contributes its good drought resistance. With the increasing knowledge in the molecular basis of WDR breeding, we can improve the procedure of WDR breeding by molecular designing. In the last two decades, 22 WDR varieties have been developed and granted national and/or local certifications after rigorous field tests (Luo et al., 2019Luo L. Mei H. Yu X. Xia H. Chen L. Liu H. Zhang A. Xu K. Wei H. Liu G. et al.Water-saving and drought-resistance rice: from the concept to practice and theory.Mol. Breed. 2019; 39: 145Crossref Scopus (19) Google Scholar), which covers more than two-thirds of the provinces in China (Figure 1A ). WDR varieties are equivalent to elite paddy rice in terms of yield and quality but also possess high WUE and good drought resistance (Luo et al., 2019Luo L. Mei H. Yu X. Xia H. Chen L. Liu H. Zhang A. Xu K. Wei H. Liu G. et al.Water-saving and drought-resistance rice: from the concept to practice and theory.Mol. Breed. 2019; 39: 145Crossref Scopus (19) Google Scholar). For example, the WUE of WDR ranges from 7.32 to 7.69 (kg∗ha−1∗mm rainfall−1), while that of elite paddy rice ranges from 5.27 to 6.99 (kg∗ha−1∗mm rainfall−1) in drip-irrigated fields (Modinat et al., 2014Modinat A.A. Liu Z.C. Vered E. Zhou L.G. Kong D.Y. Qin J.Y. Ma R.F. Yu X.Q. Liu G.L. Chen L. et al.Agronomic and ecological evaluation on growing water-saving and drought-resistant rice (Oryza sativa L.) through drip irrigation.J. Agric. Sci. 2014; 6: 110-119Google Scholar). WDR varieties, such as Hanyou73 and Huhan3, can save >40% water usage without apparent yield penalty (Modinat et al., 2014Modinat A.A. Liu Z.C. Vered E. Zhou L.G. Kong D.Y. Qin J.Y. Ma R.F. Yu X.Q. Liu G.L. Chen L. et al.Agronomic and ecological evaluation on growing water-saving and drought-resistant rice (Oryza sativa L.) through drip irrigation.J. Agric. Sci. 2014; 6: 110-119Google Scholar; Bi et al., 2019Bi J.G. Tan J.S. Zhang A.N. et al.Effects of irrigation amount on yield and water use efficiency of water-saving and drought-resistance rice (WDR).Acta Agriculturae Shanghai. 2019; 35: 7-10Google Scholar), thereby shifting irrigated paddies to aerobic conditions. WDR also performs well in rainfed fields without irrigation in many experimental sites (Figure 1D; Supplemental Table 2). The annual planting area of WDR has been expanded to ∼130 000 hectares in the Yangtze River Delta area. In addition, the WDR can improve the ability of phosphorus uptake through the organic acid metabolism in roots, which contributes to its high yield in aerobic cultivation (Bi et al., 2021Bi J. Hou D. Zhang X. Tan J. Bi Q. Zhang K. Liu Y. Wang F. Zhang A. Chen L. et al.A novel water-saving and drought-resistance rice variety promotes phosphorus absorption through root secreting organic acid compounds to stabilize yield under water-saving condition.J. Clean. Prod. 2021; 315: 127992Crossref Scopus (6) Google Scholar). WDR can be directly seeded and planted like wheat. It has been adopted in non-flooding dry fields with simplified cultivation to replace many low-beneficial dry-land crops by local farmers in China (Figure 1C). WDR performs well in newly constructed terraced fields among mountain areas or in forested regions (Figure 1C). Farmers can obtain a satisfactory yield (∼9.0 tons per hectare) from WDR under diverse water-saving cultivation modes (Figure 1C) and experience extra benefits from the saved resources and labor (Zhou et al., 2019Zhou Z. Cao J.T. Yu M.L. Zhang L.X. Analysis on the promotion and planting situation of water-saving and drought-resistant rice in Lixin county and shou county of Anhui province.Crop Res. 2019; 33: 62-65Google Scholar). Moreover, in cooperation with the International Rice Research Institute, funded by the Bill and Melinda Gates Foundation and the “green super rice (GSR)” project, WDR has been tested in many African and Asian developing countries (Figure 1B). It exhibits good performance in terms of its high and stable yield under aerobic cultivation, which is earning it an excellent reputation worldwide. Besides the equivalent yield to the elite paddy rice, planting WDR following rainfed dry farming has great environmental benefits by reducing GHG emissions without apparent yield loss (Zhang et al., 2021Zhang X. Zhou S. Bi J. Sun H. Wang C. Zhang J. Drought-resistance rice variety with water-saving management reduces greenhouse gas emissions from paddies while maintaining rice yields.Agric. Ecosyst. Environ. 2021; 320: 107592Crossref Scopus (9) Google Scholar, Zhang et al., 2022Zhang X. Sun H. Bi J. Yang B. Zhang J. Wang C. Zhou S. Estimate greenhouse gas emissions from water-saving and drought-resistance rice paddies by deNitrification-deComposition model.Clean. Technol. Environ. Policy. 2022; 24: 161-171Crossref Scopus (2) Google Scholar). In a recent 2-year field experiment (2019–2020), the cultivation of Hanyou73 in aerobic cultivations reduced CH4 emissions by 97.2% (90.71%–99.69%) in Anhui Province compared with common rice varieties with flooding cultivation (Figure 1E; Supplemental Table 3). Given the rapid development and commercialization of WDR, we can optimize the planting area of ∼670 000 hectares in China over the next 5 years, which has been projected in a current program for the high-quality development of seed industry in Shanghai. This means an annual reduction of 156 100 tons of CH4 emissions (∼4 370 000 tons of carbon dioxide equivalent) from rice paddies by replacement with WDR in total (Supplemental methods). Once the reduced carbon dioxide equivalent by WDR cultivation can be exchanged in the market, it can provide an extra benefit of up to $43.7 million for farmers annually (Supplemental methods). In the upcoming era of sustainable agriculture, the yield-prior strategy, in which how to obtain a higher yield is the first consideration in rice breeding, should be rebuilt with environment-friendly considerations. This requires great progress in crop germplasm innovation to produce resource- and labor-saving varieties and advances in simplified cultivation technologies. As a part of GSR (Luo et al., 2019Luo L. Mei H. Yu X. Xia H. Chen L. Liu H. Zhang A. Xu K. Wei H. Liu G. et al.Water-saving and drought-resistance rice: from the concept to practice and theory.Mol. Breed. 2019; 39: 145Crossref Scopus (19) Google Scholar; Yu et al., 2022Yu S. Ali J. Zhou S. Ren G. Xie H. Xu J. Yu X. Zhou F. Peng S. Ma L. et al.From Green Super Rice to green agriculture: reaping the promise of functional genomics research.Mol. Plant. 2022; 15: 9-26Abstract Full Text Full Text PDF PubMed Scopus (10) Google Scholar), WDR is bred through conventional methods by applying recurrent selections under diverse environments to improve its ability to adapt to changing environments (Luo et al., 2019Luo L. Mei H. Yu X. Xia H. Chen L. Liu H. Zhang A. Xu K. Wei H. Liu G. et al.Water-saving and drought-resistance rice: from the concept to practice and theory.Mol. Breed. 2019; 39: 145Crossref Scopus (19) Google Scholar). WDR is triggering the rice blue revolution in China, which frees rice cultivation from irrigation, labor-intensive practices, and GHG emissions. The GSR variety and its environment-friendly cultivation, as represented by WDR, will replace the conventional cultivation of paddy rice with a rebuilt balance between productivity and GHG emissions. This innovation in rice germplasm can make significant contributions to the food security and mitigation of global warming. However, there are still many scientific questions underlying the research and development of WDR. Further studies on the genetic basis of rice adaptation to dry-field cultivation and on genetic resources contributing to WUE and drought resistance in upland rice might be essential. Once we have more knowledge about these aspects, new molecular design breeding strategies may be developed and joint efforts from the scientists, breeders, farmers, and policy-makers that adopt new strategies would help achieve the sustainable rice production with fewer resources and GHG emissions in the future. FundingThis work is funded by the Shanghai Agriculture Applied Technology Development Program ( T20210104 and G2016060301 ), the National Key Research and Development Program of China ( 2018YFE0106200 ), and the Shanghai Natural Science Foundation ( 20ZR1449300 ).

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