Drought Resistance In Rice Research Articles

Dissecting Genetic Basis of Deep Rooting in Dongxiang Wild Rice

Deep rooting is an important trait in rice drought resistance. Genetic resources of deep-rooting varieties are valuable in breeding of water-saving and drought-resistant rice. In the present study, 234 BC2F7 backcross introgression lines were derived from a cross of Dongye 80 (an accession of Dongxiang wild rice as the donor parent) and R974 (an indica restorer line as the recurrent parent). A genetic linkage map containing 1 977 bin markers was constructed by ddRADSeq for QTL analysis. Thirty-one QTLs for four root traits (the number of deep roots, the number of shallow roots, the total number of deep roots and the ratio of deep roots) were assessed on six rice chromosomes in two environments (2020 Shanghai and 2021 Hainan). Two of the QTLs, qDR5.1 and qTR5.2, were located on chromosome 5 in a 70-kb interval. They were detected in both environments. qDR5.1 explained 13.35% of the phenotypic variance in 2020 Shanghai and 12.01% of the phenotypic variance in 2021 Hainan. qTR5.2 accounted for 10.88% and 10.93% of the phenotypic variance, respectively. One QTL (qRDR2.2) for the ratio of deep roots was detected on chromosome 2 in a 210-kb interval and accounted for 6.72% of the phenotypic variance in 2020. The positive effects of these three QTLs were all from Dongxiang wild rice. Furthermore, nine and four putative candidate genes were identified in qRDR2.2 and qDR5.1/qTR5.2, respectively. These findings added to our knowledge of the genetic control of root traits in rice. In addition, this study will facilitate the future isolation of candidate genes of the deep-rooting trait and the utilization of Dongxiang wild rice in the improvement of rice drought resistance.

Research on lncRNA related to drought resistance of Shanlan upland rice

BackgroundDrought has become the major abiotic stress that causes losses in rice yields and consequently is one of the main environmental factors threatening food security. Long non-coding RNA (lncRNA) is known to play an important role in plant response to drought stress, while the mechanisms of competing endogenous RNA (ceRNA) in drought resistance in upland rice have been rarely reported.ResultsIn our study, a total of 191 lncRNAs, 2115 mRNAs and 32 miRNAs (microRNAs) were found by strand-specific sequencing and small RNA sequencing to be differentially expressed in drought-stressed rice. Functional analysis of results indicate that they play important roles in hormone signal transduction, chlorophyll synthesis, protein synthesis and other pathways. Construction of a ceRNA network revealed that MSTRG.28732.3 may interact with miR171 in the chlorophyll biosynthesis pathway and affect the ability of plants to withstand drought stress by regulating Os02g0662700, Os02g0663100 and Os06g0105350. The accuracy of the regulatory network was verified by qRT-PCR.ConclusionOur results provide a theoretical basis for future studies on the potential function of lncRNA in plant drought resistance, and they provide new genetic resources for drought-resistant rice breeding.

Favorable QTLs from Oryza longistaminata improve rice drought resistance

BackgroundDrought is the major abiotic stress to rice grain production under unpredictable changing climatic environments. Wild rice of O. longistaminata show diverse responses and strong tolerance to stress environments. In order to identify whether the O. longistaminata can improve the rice drought resistance or not, a BIL population of 143 BC2F20 lines derived from the cross between the cultivar rice 9311 and O. longistaminata were assessed under stress of 20% PEG6000.ResultsIn total, 28 QTLs related to drought resistance based on eight agronomic traits of seedlings were identified. Of which, thirteen QTLs including two QTLs for leaf drying, one QTL for leaf rolling, one QTL for leaf number, five QTLs for dry weight of root, two QTLs for dry weight of shoot, one QTL for maximum root length and two QTLs for maximum shoot length were derived from O. longistaminata. What’s more, qDWR8.1 for dry weight of root was repeatedly detected and fine-mapped to an interval about 36.2 Kb. The unique allele of MH08g0242800 annotated as ATP-dependent Clp protease proteolytic subunit from O. longistaminata was suggested as the candidate gene for drought resistance. Further, six representative BIL lines were stably characterized showing significantly stronger drought resistance than 9311 based on principle component analysis, they each contained 2 ~ 5 QTLs including qDWR8.1 from O. longistaminata.ConclusionsTogether, our results indicate that the QTLs from O. longistaminata can effectively enhance the drought tolerance of rice, showing great potential value in breeding of elite rice varieties, which will lay a novel insight into the genetic network for drought tolerance of rice.

Effects of Soil Moisture Content on Germination and Physiological Characteristics of Rice Seeds with Different Specific Gravity

Soil relative water content and seed plumpness have been shown to be the key factors affecting seed germination and seedling growth of rice under direct drought cropping. It remains to be determined whether seed germination and seedling growth of water-saving and drought-resistant rice (WDR) and conventional rice with the same proportion of rice seed have the same response to soil moisture changes. The purpose of this study was to investigate the seed germination and physiological characteristics of the rice cultivars Guangliangyou 1813 (GLY-1813,indica hybrid rice) and Hanyou 73 ((HY-73), WDR) with four different specific gravities (T1, T2, T3, and T4; the rice seeds were divided into four specific gravity levels by weight using saline water, the representative specific gravities were <1.0, 1.0–1.1, 1.1–1.2 and >1.2 kg m−3, respectively), at five soil moisture content gradients (soil relative water contents of 10–20%, 20–40%, 40–60%, 60–80%, and 80–100%), under dry direct seeding conditions. The results showed that GLY-1813 had a higher germination potential, germination and seedling emergence rates, greater root dry weight, seedling dry weight, root oxidation activity, and chlorophyll content, and lower malondialdehyde (MDA) content when the soil relative water content was 20–40% or 40–60%. Cultivar HY-73 had the highest germination rate and seedling physiological activity at 20–40% relative water content; its growth vigor was better than that of GLY-1813 at the same soil moisture level. In conclusion, the soil relative water content for seed germination of HY-73 was 20–40%, which was less than that of GLY-1813. When soil relative water content was sufficient for seed germination and growth, the higher the plumpness of the rice seed, the easier it was to resist the negative effects of an adverse growth environment.

Application of consecutive polyethylene glycol treatments for modeling the seminal root growth of rice under water stress

The response of root growth to various osmotic potentials is quite important in assessing the drought resistance of rice. This study modeled seminal root growth by applying consecutive polyethylene glycol (PEG) treatments (from 0 to 25%, 1% step), mathematical equations and noncontact image analysis to quantitatively evaluate the root response. Treatment began after seeds were germinated, and root growth was recorded by a digital camera every day from 7 to 20 days after seeding (DAS). Although the seminal root length (SRL) measured by image analysis slightly varied with DAS, the equations explained the differences in SRL increases under each PEG concentration relatively well (R2 = 0.774). The equations also suggested that the maximum seminal root length was observed at 5.9% PEG. This numerical characterization of root growth is an effective means of evaluating drought resistance.

Molecular Breeding of a Novel PTGMS Line of WDR for Broad-Spectrum Resistance to Blast Using Pi9, Pi5, and Pi54 Genes

BackgroundThe two-line method based on the photoperiod and thermo-sensitive genic male sterile (PTGMS) lines is more cost-effective, simple, and efficient than the three-line system based on cytoplasmic male-sterility. Blast and drought are the most prevalent biotic and abiotic stress factors hampering rice production. Molecular techniques demonstrate higher efficacy in the pyramiding of disease resistance genes, providing green performance under the background of water-saving and drought-resistance rice.ResultsThis study employed molecular marker-assisted selection, conventional hybridization, and high-intensity stress screening to integrate three broad-spectrum blast resistance genes Pi9, Pi5, and Pi54 into Huhan 1S. Subsequently, a novel water-saving and drought-resistance rice (WDR) PTGMS line Huhan 74S was developed. The drought resistance of the new PTGMS line Huhan 74S was comparable to that of Huhan 1S. Pathogenicity assays involving the inoculation of 14 blast prevalent isolates in the glasshouse showed that the blast resistance frequency of Huhan 74S was 85.7%. Further evaluation under natural blast epidemic field conditions showed that Huhan 74S and its hybrids were resistant to leaf and neck blast. The critical temperature point of fertility-sterility alteration of Huhan 74S was 23 °C daily mean temperature. The complete male sterility under natural growth conditions in 2017 at Shanghai lasted for 67 days. Also, both the agronomic and grain quality traits met the requirement for two-line hybrid rice production.ConclusionThese results indicate that the newly bred PTGMS line Huhan 74S can be used to breed high-yielding, good-quality, disease-resistant two-line hybrid water-saving and drought-resistance rice (WDR), hence promoting sustainable rice production in China.

Correction to: Physiological Mechanism of Drought-Resistant Rice Coping With Drought Stress

Correction to: Physiological Mechanism of Drought-Resistant Rice Coping With Drought Stress

Ipa1 improves rice drought tolerance at seedling stage mainly through activating abscisic acid pathway.

KEY MESSAGE: ipa1 enhances rice drought tolerance mainly through activating the ABA pathway. It endows rice seedlings with a more developed root system, smaller leaf stomata aperture, and enhanced carbon metabolism. Drought is a major abiotic stress to crop production. IPA1 (IDEAL PLANT ARCHITECTURE 1)/OsSPL14 encodes a transcription factor and has been reported to function in both rice ideal plant architecture and biotic resistance. Here, with a pair of IPA1 and ipa1-NILs (Near Iso-genic Lines), we found that ipa1 could significantly improve rice drought tolerance at seedling stage. The ipa1 plants had a better-developed root system and smaller leaf stomatal aperture. Analysis of carbon-nitrogen metabolism-associated enzyme activity, gene expression, and metabolic profile indicated that ipa1 could tip the carbon-nitrogen metabolism balance towards an increased carbon metabolism pattern. In both the control and PEG-treated conditions, ABA content in the ipa1 seedlings was significantly higher than that in the IPA1 seedlings. Expression of the ABA biosynthesis genes was detected to be up-regulated, whereas the expression of ABA catabolism genes was down-regulated in the ipa1 seedlings. In addition, based on yeast one-hybrid assay and dual-luciferase assay, IPA1 was found to directly activate the promoter activity of OsHOX12, a transcription factor promoting ABA biosynthesis, and OsNAC52, a positive regulator of the ABA pathway. The expression of OsHOX12 and OsNAC52 was significantly up-regulated in the ipa1 plants. Combined with the previous studies, our results suggested that ipa1 could improve rice seedling drought tolerance mainly through activating the ABA pathway and that regulation of the ipa1-mediated ABA pathway will be an important strategy for improving drought resistance of rice.

Photosynthetic physiological response of water-saving and drought-resistant rice to severe drought under wetting-drying alternation irrigation.

Water-saving and drought-resistant rice (WDR) is widely grown in central China in recent years. However, studies have not explored the interaction effect of WDR and irrigation regimes on drought-resistance capacities under severe drought at sensitive growth periods. A pot experiment was conducted using a WDR cultivar Hanyou73 (HY73) and traditional high-yielding and drought-sensitive cultivar Huiliangyou 898 (HLY898). Three irrigation regimes, including flooding irrigation (W1), mild wetting-drying alternation irrigation (W2), and severe wetting-drying alternation irrigation (W3), were applied before heading. At heading, severe drought with -50 KPa soil water potential was established for all treatments and cultivars. The findings showed that cultivar HY73 under W2 treatment had the highest yield, 1000-grain yield, filled grain, relative water content, and photosynthesis potential compared with the other combinations. The higher net photosynthetic rate (Pn ) was attributed to larger mesophyll conductance (gm ) in drought for cultivar HY73 under W2 treatment compared with that for cultivar HLY898 and the other water treatments. Enhanced photo-respiration rate may be an important photoprotection mechanism for achieving high Pn for cultivar HY73 coupled with W2 treatment than for other combinations in drought. The relative expression level of OsPIP1;1 gene was significantly down-regulated during drought in all cultivars and water regimes. But OsPIP1;2, OsPIP2;3, OsTIP2;2, and OsTIP3;1 genes were upregulated to alleviate the significant decrease in gs and gm under drought. These results suggest that WDR and mild wetting-drying alternation irrigation (W2) have significant interaction effects in improving photosynthetic production potential by maintaining higher gm under severe drought.

Physiological Mechanism of Drought-Resistant Rice Coping With Drought Stress

Drought stress is one of the major threats to rice production. The weakening of leaf photosynthesis due to drought is the main reason for the reduction of grain yield, but its mechanism is still obscure. The objectives of this study were to reveal the physiological mechanism of drought stress affecting photosynthetic capacity and grain yield. Pot experiments were conducted with drought-tolerant cultivars Hanyou113 (HY113) and Zhonghan3 (ZH3) and drought-sensitive cultivar Huanghuazhan (HHZ) under four water management treatments (traditional flooding (CK), mild drought stress (LD), moderate drought stress (MD) and severe drought stress (HD)) at heading stage in 2013 and 2014. Compared with CK, grain yield was significantly reduced by 14.9%, 30.8%, and 12.8% in HY113, HHZ, and ZH3 under LD, 32.9%, 33.7%, and 22.9% in HY113, HHZ and ZH3 under MD and 53.6%, 45.6%, and 30.7% in HY113, HHZ, and ZH3 under HD, respectively. The photosynthetic rate (Pn) decreased by 49.0% from 20.0 to 10.2 µmol m−2 s−1 in HY113, and 67.6% from 23.4 to 7.58 µmol m−2 s−1 in HHZ, and 39.3% from 23.4 to 14.2 µmol m−2 s−1 in ZH3 under HD. The Pn of HHZ was similar to that of ZH3 under CK conditions. During the drought periods from LD to HD at heading stage, the leaf water potential (LWP) reduced 31.9%, 54.8%, and 15.7% in HY113, HHZ, and ZH3, respectively. The non-photochemical quenching (NPQ) of HY113, HHZ, and ZH3 flag leaves increased by 150%, 97.6%, and 218%, respectively. The effective quantum yield of PSII photochemistry (ΦPSII) of flag leaves reduced by 20.3%, 11.9%, and 22.1% in HY113, HHZ, and ZH3, respectively. The enzymatic activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) increased by 11.4%, 18.0%, and 21.8% in HY113, and 13.2%, 14.3%, and 30.9% in HHZ, and 13.4% 21.7%, and 17.6% in ZH3 under MD on average across two seasons. The yield reduction of drought-resistant cultivars (HY113, ZH3) was smaller than that of conventional cultivars (HHZ). Maintaining leaf water potential (LWP), Pn, photosystem II (PSII) original light energy conversion efficiency, non–photochemical quenching coefficient (NPQ), and increasing in the ratio of photochemical reaction energy in fluorescence and antioxidant enzyme activity is the physiological basis to achieve a relatively high photosynthesis. These traits could be the target for breeder to develop drought-tolerant varieties.

LncRNA TCONS_00021861 is functionally associated with drought tolerance in rice (Oryza sativa L.) via competing endogenous RNA regulation

BackgroundWater deficit is an abiotic stress that retards plant growth and destabilizes crop production. Long non coding RNAs (lncRNAs) are a class of non-coding endogenous RNAs that participate in diverse cellular processes and stress responses in plants. lncRNAs could function as competing endogenous RNAs (ceRNA) and represent a novel layer of gene regulation. However, the regulatory mechanism of lncRNAs as ceRNA in drought stress response is yet unclear.ResultsIn this study, we performed transcriptome-wide identification of drought-responsive lncRNAs in rice. Thereafter, we constructed a lncRNA-mediated ceRNA network by analyzing competing relationships between mRNAs and lncRNAs based on ceRNA hypothesis. A drought responsive ceRNA network with 40 lncRNAs, 23 miRNAs and 103 mRNAs was obtained. Network analysis revealed TCONS_00021861/miR528-3p/YUCCA7 regulatory axis as a hub involved in drought response. The miRNA-target expression and interaction were validated by RT-qPCR and RLM-5’RACE. TCONS_00021861 showed significant positive correlation (r = 0.7102) with YUCCA7 and negative correlation with miR528-3p (r = -0.7483). Overexpression of TCONS_00021861 attenuated the repression of miR528-3p on YUCCA7, leading to increased IAA (Indole-3-acetic acid) content and auxin overproduction phenotypes.ConclusionsTCONS_00021861 could regulate YUCCA7 by sponging miR528-3p, which in turn activates IAA biosynthetic pathway and confer resistance to drought stress. Our findings provide a new perspective of the regulatory roles of lncRNAs as ceRNAs in drought resistance of rice.

Genome-Wide Bisulphite Sequencing Uncovered the Contribution of DNA Methylation to Rice Short-Term Drought Memory Formation

Rice is the important crop for more than half of the world population. However, drought can have a devastating impact on rice growth and reduce yield drastically. Understanding the response of rice to drought stress is especially important for crop breeding. Previously we found that rice enhanced its tolerance to drought stresses via stress memory mechanisms. Numerous memory genes were identified to play important roles in the process. DNA methylation was reported to mediate tolerance via regulating gene expression and enhances the survival rate of rice encountering drought stress. However, how DNA methylation involved in stress memory is still not clear. In this study, genome-wide bisulphite sequencing at a single base resolution methylome profiling level was performed and analyzed in rice cultivar under recurrent drought stresses and recovery treatments. We found that rice drought stress memory-related differentially methylated regions (DMRs) showed dynamic and distinct patterns. The drought-memory DMRs may regulate Transposable elements and gene expression to cope with short-term repeated drought stresses. Our findings of drought-memory DMRs can explain mechanisms of rice drought stress memory in a new perspective on global methylome details. Using epigenetic markers to breed drought-resistant rice would become a feasible way in the future research.

Quantitative Trait Loci and Candidate Gene Identification for Chlorophyll Content in RIL Rice Population under Drought Conditions

Rice (Oryza sativa) is the staple food for more than half of the world population. Rice needs 2-3 times more water compared to other crops. Drought condition is one of the limited factor in rice production. Recombinant inbred line population derived from a cross between rice genotype tropical japonica Kaybonnet and indica ZHE733 named K/Z RIL population was used to identify candidate genes for chlorophyll content related to grain yield under drought condition. Chlorophyll content in the flag leaf of the rice plant is related to the grain yield since chlorophyll plays an important role in the photosynthesis. The K/Z RIL population was screened in the field at Fayetteville, Arkansas, USA by controlled drought stress treatment at the reproductive stage (R3), and the effect of drought stress was quantify by measuring chlorophyll content, flag leaf characteristics, and grain yield. Quantitative trait loci (QTL) analysis was performed with a set of 4133 single nucleotide polymorphism (SNP) markers by using QTL IciMapping software version 4.2.53. Candidate genes within the QTL regions were identified by using the MSU Rice Genome Annotation Project database release 7.0 as the reference. A total of eleven QTLs and forty-three candidate genes were identified for chlorophyll content related to the grain yield under drought condition. Most of the candidate genes involve in biological processes, molecular functions, and cell components. By understanding the genetic complexity of the chlorophyll content, this research provides information to develop drought-resistant rice varieties with greater productivity under drought stress condition.

Drought-resistance rice variety with water-saving management reduces greenhouse gas emissions from paddies while maintaining rice yields

Rice paddies are a major anthropogenic source of greenhouse gas (GHG) emissions due to the flooding management. Water saving practices often reduce the GHG emissions from rice paddies, yet increase the risk of rice yields loss due to drought stress. Water-saving and drought-resistance rice (WDR) has high drought-tolerant, suggesting that WDR with water-saving management could reduce GHG emissions while maintaining rice yields. However, the effect of WDR on GHG emissions is still unclear. Therefore, we conducted a 2-yr field experiment to assess the effect of WDR on rice yields and GHG emissions under continuous flooding (F), alternate wetting and drying (AWD), and dry cultivation (D) conditions, using a WDR variety and a common variety. Compared to the common variety, the WDR did not affect the rice yields under F and AWD treatments, but increased rice yields by 24% under D treatment. The methane (CH4) emissions and nitrous oxide (N2O) emissions of the two rice varieties were similar. Compared to the F treatment, AWD treatment reduced CH4 emissions by 7%−64% and area-scaled global warming potential (GWP) by 9%−39% and D treatment reduced CH4 emissions by 70%−90% and area-scaled GWP by 65%−74%. The WDR with dry cultivation (D-WDR mode) had the lowest area- and yield-scaled GWP. Our findings indicate that it is possible to produce optimal rice yields with low GHG emissions in the D-WDR mode, and suggest that drought-resistance rice variety breeding may benefit climate change mitigation and adaptation efforts.

Comparison of the F2 and F3 traits’ inheritance by the rice hybrid ‘Kontro x Kuboyar’

Rice is a very moisture-loving crop, therefore it suffers greatly from drought. However, in the world in recent years, there is an increasing shortage of fresh water, which makes the use of upland rice relevant. Therefore, rice varieties with a reduced demand for water supply, developed as a result of breeding work, are more profitable for agricultural producers than agrotechnical or reclamation measures. It is much cheaper to produce such rice with periodic irrigation. The purpose of the current study was to analyze genetically the main quantitative traits of the rice hybrid ‘Kontro x Kuboyar’ with the selection of the best forms for subsequent breeding for drought resistance. The study was carried out in 2019–2020 on the rice plots of the special subdivision ‘Proletarskoye’ belonging to of the Agricultural Research Center “Donskoy” in the Rostov Region. In the course of the study there has been made a genetic analysis of a number of quantitative traits that determine rice productivity. The character of traits’ inheritance in the second and third generations was identical. The inheritance of the trait ‘panicle length’ was characterized by partial negative dominance and monogenic differences in parental varieties. The trait ‘number of spikelets per panicle’ was inherited according to the type of negative dominance of smaller values of the trait and was determined by the interaction of two pairs of genes. The trait ‘1000-kernel weight’ was identified by the partial dominance of large values of the trait and monogenic differences in the parental varieties. The traits ‘kernel length’ and ‘kernel width’ were split according to the monohybrid scheme 1:2:1, and there was no dominance. From the third generation, the best early-maturing forms with optimal values of the traits ‘plant height’, ‘panicle length’, ‘1000-kernel weight’ and ‘the best kernel percentage per panicle’ were selected for the subsequent breeding of drought-resistant rice varieties.

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

More than 70% of global rice production depends on irrigation water, which has brought on a progressive reduction in the groundwater table. Further groundwater withdrawal are unsustainable for future rice production. Sustainable rice production calls for the use of resource-saving and environmentally friendly rice varieties. This study investigated the morphological and physiological mechanisms of biomass and tissue phosphorus accumulation in a water-saving and drought-resistance rice variety (Hanyou73) and a normal paddy rice variety (Hyou518) under different water management regimes. The two rice cultivars were grown in pot experiments carried out with factorial combinations of three water regimes, conventional irrigation (high irrigation rate, HR), 60% of conventional irrigation (medium irrigation rate, MR), and 20% of conventional irrigation (low irrigation rate, LR) for four-years. While the grain yield of Hanyou73 was similar as Hyou518 under HR, it was significantly higher than Hyou518 under MR and LR. Under deficit irrigation, the tissue-specific biomass of Hanyou73 was higher than that of Hyou518, and the total P accumulation of Hanyou73 was 70% greater than that of Hyou518. Meanwhile, the root growth, root oxidation activity, and absorption area of Hanyou73 under the MR and LR treatments were significantly higher than those of Hyou518. Analysis of root exudate metabolites revealed an abundance of organic acids produced by the Hanyou73 roots under, which may account for its higher P uptake. Overall, the findings of this study indicate that Hanyou73 promoted P uptake to maintain higher yields under deficit irrigation. The higher P uptake by Hanyou73 may be related to its altered root physiology, which may be the mechanism by which Hanyou73 adapts to water saving irrigation conditions and maintains its yield traits.

Using Network-Based Machine Learning to Predict Transcription Factors Involved in Drought Resistance.

Gene regulatory networks underpin stress response pathways in plants. However, parsing these networks to prioritize key genes underlying a particular trait is challenging. Here, we have built the Gene Regulation and Association Network (GRAiN) of rice (Oryza sativa). GRAiN is an interactive query-based web-platform that allows users to study functional relationships between transcription factors (TFs) and genetic modules underlying abiotic-stress responses. We built GRAiN by applying a combination of different network inference algorithms to publicly available gene expression data. We propose a supervised machine learning framework that complements GRAiN in prioritizing genes that regulate stress signal transduction and modulate gene expression under drought conditions. Our framework converts intricate network connectivity patterns of 2160 TFs into a single drought score. We observed that TFs with the highest drought scores define the functional, structural, and evolutionary characteristics of drought resistance in rice. Our approach accurately predicted the function of OsbHLH148 TF, which we validated using in vitro protein-DNA binding assays and mRNA sequencing loss-of-function mutants grown under control and drought stress conditions. Our network and the complementary machine learning strategy lends itself to predicting key regulatory genes underlying other agricultural traits and will assist in the genetic engineering of desirable rice varieties.

Estimate greenhouse gas emissions from water-saving and drought-resistance rice paddies by deNitrification-deComposition model

Flooded rice fields have been confirmed as a major anthropogenic source of atmospheric methane (CH4). Avoiding continuous flooding is an effective practice to mitigate the CH4 emissions originating from paddy fields. However, the contradiction between the high yield and water consumption of paddy rice limits the mitigation potential of greenhouse gas (GHG) emissions through a dramatic reduction in water usage. Recently, a new rice type, water-saving and drought-resistance rice (WDR), has been developed to satisfy both the rice yield and quality with a high water use efficiency and good drought resistance. WDR can be planted under dry cultivation, similar to upland crops. A biogeochemical process model, DNDC (i.e., DeNitrification-DeComposition) was used to evaluate the effect of agricultural practices (F-R as paddy rice under flooding management and D-WDR as WDR under dry cultivation) on GHG emissions from paddy fields in Anhui Province, China. The results are as follows: 1) the DNDC model attained a good performance when simulating the rice yield, seasonal cumulative CH4 and N2O emissions, and GWP; 2) the mitigation potential of the D-WDR system was higher than 90% while maintaining a high rice yield; 3) if rice paddies in Anhui can be replaced by D-WDR system, the GHG mitigation potential could reach 16.92 Mt CO2-eq, and the increased N2O emissions of the WDR system could offset a small fraction (7.6%) of the GHG radiated forcing benefit gained by the decrease in CH4 emissions. Shifting rice production from paddy rice to WDR has a remarkable potential to balance the relationship between CH4 mitigation and rice yield maintenance.

Effects of irrigation regime and rice variety on greenhouse gas emissions and grain yields from paddy fields in central China

Increasing irrigation water scarcity is threatening global rice production and sustainability. Accordingly, the cultivation of drought-resistant rice varieties has been strongly advocated to reduce the consumption of irrigation water. However, it remains unclear how the cultivation of drought-resistant rice affects greenhouse gas emissions. Here, a two-year field experiment was conducted to elucidate the effects of irrigation regimes (AWD, alternate wetting and drying; CF, continuous flooding) and rice varieties (drought-resistant rice 7Y88 and 7Y370, and conventional rice HHZ) on the grain yields and greenhouse gas (methane [CH4] and nitrous oxide [N2O]) emissions from paddy fields. The experiment was performed in a split-plot design with three replications. The results showed that AWD significantly reduced water inputs and grain yields compared with CF in both rice growing seasons. On average, 7Y88 and 7Y370 significantly enhanced the water use efficiency by 37.6% and 51.5%, and the grain yields by 33.9% and 47.0% relative to HHZ, respectively. A trade-off between CH4 and N2O emissions was observed under irrigation regimes. Compared with CF, AWD significantly reduced cumulative CH4 emissions by 64.9%, while increased cumulative N2O emissions by 160.0%, and decreased the grain yield by 11.6% on average. AWD also significantly reduced the global warming potential (GWP) and greenhouse gas intensity (GHGI) by 42.2% and 31.6%, respectively. Significant differences (p < 0.05) in GHG emissions, GWP and GHGI were observed between drought-resistant rice varieties and HHZ. The rice variety 7Y370 resulted in the lowest CH4 and N2O emissions, GWP and GHGI among all varieties under both irrigation regimes. These results indicate that the rice variety 7Y370 can be recommended to simultaneously mitigate GWP and maintain grain yields.

A critical review on the improvement of drought stress tolerance in rice (Oryza sativa L.)

Abiotic stresses are the primary threat to crop production across the globe. Drought stress is primary abiotic stress which is considerably limiting the global rice production and putting the food security at higher risks. Drought tolerance (DT) is a multigene trait which is influenced by various stages of development in rice plant. Tolerance as well as susceptibility of rice to drought stress is carried out by different drought-response genes and other components of stress. Plant researchers have used various methods such as, genetic manipulation and marker-assisted techniques for development of new rice cultivars with improved tolerance to drought stress. The aims of this review are to present recent advancements and illustrate current approaches to breed a robust drought-resistant rice genotypes by using classical breeding and advanced molecular techniques. We also shed light on all available information regarding the role of significant hormones in DT, QTL for drought-related traits, QTL for rice yield, global strategies for the improvement of DT in rice, DT genes, and selection supported by markers.