Grain Yield Of Rice Research Articles

Receptor-Like Cytoplasmic Kinase STK Confers Salt Tolerance in Rice

BackgroundSoil salinization is a major abiotic environmental stress factor threatening crop production throughout the world. Salt stress drastically affects the growth, development, and grain yield of rice (Oryza sativa L.), and the improvement of rice tolerance to salt stress is a desirable approach for meeting increasing food demand. Receptor-like cytoplasmic kinases (RLCKs) play essential roles in plant growth, development and responses to environmental stresses. However, little is known about their functions in salt stress. Previous reports have demonstrated that overexpression of an RLCK gene SALT TOLERANCE KINASE (STK) enhances salt tolerance in rice, and that STK may regulate the expression of GST (Glutathione S-transferase) genes.ResultsThe expression of STK was rapidly induced by ABA. STK was highest expressed in the stem at the heading stage. STK was localized at the plasma membrane. Overexpression of STK in rice increased tolerance to salt stress and oxidative stress by increasing ROS scavenging ability and ABA sensitivity. In contrast, CRISPR/Cas9-mediated knockout of STK increased the sensitivity of rice to salt stress and oxidative stress. Transcriptome sequencing analysis suggested that STK increased the expression of GST genes (LOC_Os03g17480, LOC_Os10g38140 and LOC_Os10g38710) under salt stress. Reverse transcription quantitative PCR (RT-qPCR) suggested that four stress-related genes may be regulated by STK including OsABAR1, Os3BGlu6, OSBZ8 and OsSIK1.ConclusionsThese findings suggest that STK plays a positive regulatory role in salt stress tolerance by inducing antioxidant defense and associated with the ABA signaling pathway in rice.

Integrated strength of osmotic potential and phosphorus to achieve grain yield of rice under water deficit by arbuscular mycorrhiza fungi

Arbuscular mycorrhizal ecosystem provides sustainability to plant integrity under drought situations. However, host plants that survive in drought frequently lose yield. The potential of Funneliformis mosseae (F), Claroideoglomus etunicatum (C), and Acaulospora fovaeta (A) was assessed to evaluate in indica rice cv. Leum Pua during booting stage under 21-day water withholding. The effects of three inoculation types; (i) F, (ii) F + C (FC), and (iii) F + C + A (FCA), on physiological, biochemical, and yield traits were investigated. The three types showed an induced total chlorophyll content in the host as compared to uninoculated plants. Total soluble sugars and free proline were less regulated by FC and FCA inoculated plants than by F inoculated plants under water deficit conditions. However, the FC and FCA inoculations increased phosphorus content, particularly in the shoots of water-stressed plants. In the three inoculations, the FCA dramatically improved plant osmotic potential adaptability under water deficit stress. Furthermore, even when exposed to the water deficit condition, panicle weight, grain number, and grain maturity were maintained in FCA inoculated plants. According to the findings, the increased osmotic potential and phosphorus content of the FCA-inoculated rice plant provide a protection sign against drought stress and will benefit food security in the future.

Chloroplastic Sec14-like proteins modulate growth and phosphate deficiency responses in Arabidopsis and rice.

Phosphorus is an essential nutrient acquired from soil as phosphate (Pi), and its deficiency severely reduces plant growth and crop yield. Here, we show that single nucleotide polymorphisms (SNPs) at the PHOSPHATIDYLINOSITOL TRANSFER PROTEIN7 (AtPITP7) locus, which encodes a chloroplastic Sec14-like protein, are associated with genetic diversity regarding Pi uptake activity in Arabidopsis (Arabidopsis thaliana). Inactivation of AtPITP7 and its rice (Oryza sativa) homolog (OsPITP6) through T-DNA insertion and CRISPR/Cas9-mediated gene editing, respectively, decreased Pi uptake and plant growth, regardless of Pi availability. By contrast, overexpression of AtPITP7 and OsPITP6 enhanced Pi uptake and plant growth, especially under limited Pi supply. Importantly, overexpression of OsPITP6 increased tiller number and grain yield in rice. Targeted metabolome analysis of glycerolipids in leaves and chloroplasts revealed that inactivation of OsPITP6 alters phospholipid contents, independent of Pi availability, diminishing the reduction in phospholipid content and increase in glycolipid content induced by Pi deficiency; meanwhile, overexpression of OsPITP6 enhanced Pi deficiency induced metabolic alterations. Together with transcriptome analysis of ospitp6 rice plants and phenotypic analysis of grafted Arabidopsis chimeras, these results suggest that chloroplastic Sec14-like proteins play an essential role in growth modulations in response to changes in Pi availability, although their function is critical for plant growth under any Pi condition. The superior traits of OsPITP6-overexpressing rice plants also highlight the potential of OsPITP6 and its homologs in other crops as additional tools for improving Pi uptake and plant growth in low Pi environments.

Effect of Nitrogen Fertilizer and Plant Density on Growth Characteristics, Yield Components and Grain Yield of Rice

Effect of Nitrogen Fertilizer and Plant Density on Growth Characteristics, Yield Components and Grain Yield of Rice

OsCYBDOMG1, a cytochrome b561 domain-containing protein, regulates salt tolerance and grain yield in rice

OsCYBDOMG1 positively regulates salt tolerance, plant growth, and grain yield by affecting ascorbate biosynthesis and redox state. Soil salinity is a major abiotic stress affecting rice growth and productivity. Many genes involved in the salt stress response have been identified, but the precise mechanisms underlying salt tolerance remain unclear. In this study, we isolated a salt-sensitive mutant of rice, rss5, which exhibited more severe wilting and chlorosis with a significant increase in lipid peroxidation, electrolyte leakage, and shoot Na+ concentration compared to wild-type plants. Map-based cloning, MutMap analysis, and genetic complementation revealed that a single-nucleotide mutation in a gene encoding a cytochrome b561 domain-containing protein (OsCYBDOMG1) was responsible for the mutant phenotype of rss5. The OsCYBDOMG1 gene was mainly expressed in young shoots and nodes, and the encoded protein was principally located in the plasma membrane and endoplasmic reticulum. Mutations of OsCYBDOMG1 resulted in decreased ascorbic acid (AsA) content and AsA/DHA (dehydroascorbate) ratio, which led to increased H2O2 accumulation and reduced salt tolerance. Moreover, plant growth and grain yield of rss5 and the OsCYBDOMG1 knockout mutant (cr-1) were significantly decreased compared to wild-type plants under normal conditions. The elite haplotype of OsCYBDOMG1 associated with higher salt tolerance and grain width and weight was mainly existed in japonica varieties. These results suggest that OsCYBDOMG1 plays an important role in the regulation of salt tolerance, plant growth, and grain yield in rice.

Ectopic co-expression of endosome located V-ATPase subunit gene and NHX transporter gene from Helianthus tuberosus enhances rice growth and nutrient uptake

V-type H+-ATPase (VHA) at vacuolar and endosome systems can provide the driving force for activating intracellular Na+(K+)/H+ (NHX) antiporters. We have previously shown that expression of an endosomal located HtNHX2 from Helianthus tuberosus increased rice tolerance to K+-limited salt stress or general deficiency of nutrients. In this study, we cloned HtVHA-c” also from Helianthus tuberosus and found that HtVHA-c” is mainly located on endosome and trans-Golgi network/Golgi network. Expression of HtVHA-c” enhanced salt-tolerance of BY2 cells at the cellular level and growth of rice at salt-stress by increasing K+ acquisition. Co-expression of HtVHA-c” and HtNHX2 could further promote K+ uptake and increase growth and grain yield of rice at non-salt-stress and sufficient nutrient supply condition in both hydroponic culture and paddy field. Notably, HtVHA-c” acidified while HtNHX2 alkalized luminal of prevacuolar compartments/multivesicular bodies and vacuoles, while these effects were neutralized when both genes were expressed in rice. These results demonstrate the novel synergistic function of VHA-c” and NHX2 in regulating the luminal pH of endosomes for improving plant mineral nutrition and salt tolerance.

Genome-wide association study identifies a gene conferring high physiological phosphorus use efficiency in rice.

Phosphate (Pi) is indispensable for the growth and development of plant, and low-Pi stress is a major limitation for crop growth and yield worldwide. The tolerance to low-Pi stress varied among rice germplasm resources. However, the mechanisms underlying the tolerance of rice to low-Pi stress, as a complex quantitative trait, are not clear. We performed a genome-wide association study (GWAS) through a diverse worldwide collection of 191 rice accessions in the field under normal-Pi and low-Pi supply in two years. Twenty and three significant association loci were identified for biomass and grain yield per plant under low-Pi supply respectively. The expression level of OsAAD as a candidate gene from a associated locus was significantly up-regulated after low-Pi stress treatment for five days and tended to return to normal levels after Pi re-supply in shoots. Suppression of OsAAD expression could improve the physiological phosphorus use efficiency (PPUE) and grain yields through affecting the expression of several genes associated with GA biosynthesis and metabolism. OsAAD would be a promising gene for increasing PPUE and grain yield in rice under normal- and low-Pi supply via genome editing.

Assessment of Soil Fertility through Response of Rice (Oryza sativa L.) to Nutrient Omission in Alfisols of Kondagaon District of Chhattisgarh in India

The investigation was carried out with the aim to identify the specific yield limiting nutrients through response of rice to nutrient omission in pot culture under completely randomized design with 3 replications and 11 treatments during kharif season 2017 and to demonstrate the optimum use of identified limiting nutrients in wheat crop at field level in Kondagaon district during rabi season 2017-18. The treatments were formulated by keeping one treatment with application of all nutrients in optimum level and others by sequentially omitting each nutrient. The soil had a clay loam texture, neutral reaction (pH 6.6), normal electrical conductivity, medium organic C, available P and K, low available N and S, high available Ca, Mg, Fe, Mn and Cu and marginal available Zn and B. Omission of N and P nutrients significantly reduced the growth, yield and nutrients uptake by rice in comparison to all nutrients. The maximum grain yield of 73.0 g pot-1 was recorded, in all nutrients pot and 50.1 % reduction in grain yield of rice, from the maximum yield, was recorded in N omitted pots, followed by 18.8 % reduction in P omitted pots and omission of other nutrients didn’t reduce the grain yield significantly indicating that only N and P were yield limiting nutrients. In field verification during rabi season, 19.0 % increase in wheat grain yield and 23.0 % increase in net return was recorded, due to optimum dose of identified yield limiting nutrients over farmer's practice dose. The results clearly indicate that the site specific nutrient management dose based on yield limiting nutrient identified through nutrient omission study was found economically profitable to the farmers.

Impact of integrated nutrient management on crop productivity and soil fertility under rice (Oryza sativa)–chickpea (Cicer arietinum) cropping system in Chhattisgarh plain agro-climatic zone

A study was conducted during 2016–17 to 2018–19 at farmer’s field under Farmer FIRST Project (FFP), at College of Agriculture, Jawaharlal Nehru Krishi Vishwa Vidyalaya, Waraseoni, Balaghat, Jabalpur, Madhya Pradesh, to assess the impact of integrated nutrient management on crop productivity, soil-nutrient balance and economics of rice (Oryza sativa L.)–chickpea (Cicer arietinum L.) cropping system. Application of 75% NPK + 5 t/ha farmyard manure (FYM) + biofertilizers [blue green algae (BGA)/Rhizobium and phosphate-solubilizing bacteria (PSB)] resulted in significantly higher grain yield of rice and chickpea (4,429 kg/ha and 1,538 kg/ha, respectively) over the Farmer Practice (3,644 kg/ha and 1,036 kg/ha respectively). The maximum nutrients uptake (N, P and K) by rice and chickpea crops were recorded in the treatment receiving 75% NPK + 5 t/ha FYM + biofertilizers. The conjunctive use of inorganic fertilizers along with organic manure and biofertilizers exhibited the highest availability of soil N, P, K and Zn at post-harvest of chickpea crop as compared to the other treatment combinations. Further, results showed that the highest cost of cultivation (`58,200/ha) and net returns (`96,832/ha) were obtained in 75% NPK + 5 t/ha FYM + biofertilizers treatment. The benefit: cost (B: C) ratio computed for rice–chickpea cropping system indicated that, the higher B: C ratio was found to be associated with higher production and better quality of the produce.

Light intensity-mediated auxin homeostasis in spikelets links carbohydrate metabolism enzymes with grain filling rate in rice.

Low light (LL) stress during the grain-filling stage acutely impairs the quality and quantity of starch accumulation in rice grains. Here, we observed that LL-induced poor starch biosynthesis is modulated by auxin homeostasis, which regulates the activities of major carbohydrate metabolism enzymes such as starch synthase (SS) and ADP-glucose pyrophosphorylase (AGPase) in rice. Further, during the grain-filling period under LL, the starch/sucrose ratio increased in leaves but significantly decreased in the developing spikelets. This suggests poor sucrose biosynthesis in leaves and starch in the grains of the rice under LL. A lower grain starch was found to be correlated with the depleted AGPase and SS activities in the developing rice grains under LL. Further, under LL, the endogenous auxin (IAA) level in the spikelets was found to be synchronized with the expression of a heteromeric G protein gene, RGB1. Interestingly, under LL, the expression of OsYUC11 was significantly downregulated, which subsequently resulted in reduced IAA in the developing rice spikelets, followed by poor activation of grain-filling enzymes. This resulted in lowered grain starch accumulation, grain weight, panicle number, spikelet fertility, and eventually grain yield, which was notably higher in the LL-susceptible (GR4, IR8) than in the LL-tolerant (Purnendu, Swarnaprabha) rice genotypes. Therefore, we hypothesize that depletion in auxin biosynthesis under LL stress is associated with the downregulation of RBG1, which discourages the expression and activities of grain-filling enzymes, resulting in lower starch production, panicle formation, and grain yield in rice.

OsGRF4AA compromises heat tolerance of developing pollen grains in rice.

Extreme high temperature at the meiosis stage causes a severe decrease in spikelet fertility and grain yield in rice. The rice variety grain size on chromosome 2 (GS2) contains sequence variations of OsGRF4 (Oryza sativa growth-regulating factor 4; OsGRF4AA ), escaping the microRNA miR396-mediated degradation of this gene at the mRNA level. Accumulation of OsGRF4 enhances nitrogen usage and metabolism, and increases grain size and grain yield. In this study, we found that pollen viability and seed-setting rate under heat stress (HS) decreased more seriously in GS2 than in its comparator, Zhonghua 11 (ZH11). Transcriptomic analysis revealed that, following HS, genes related to carbohydrate metabolic processes were expressed and regulated differentially in the anthers of GS2 and ZH11. Moreover, the expression of genes involved in chloroplast development and photosynthesis, lipid metabolism, and key transcription factors, including eight male sterile genes, were inhibited by HS to a greater extent in GS2 than in ZH11. Interestingly, pre-mRNAs of OsGRF4, and a group of essential genes involved in development and fertilization, were differentially spliced in the anthers of GS2 and ZH11. Taken together, our results suggest that variation in OsGRF4 affects proper transcriptional and splicing regulation of genes under HS, and that this can be mediated by, and also feed back to, carbohydrate and nitrogen metabolism, resulting in a reduction in the heat tolerance of rice anthers.

Effect of nitrogen management on grain yield of rice grown in a high-yielding environment under flooded and non-flooded conditions

With increased cost and scarcity of irrigation water, flooded rice growing system may need to be replaced with water-saving technologies which includes part or complete removal of flooding and to be replaced with non-flooded aerobic conditions. However, to maintain high grain yield equivalent to that achieved with flooded rice, nitrogen (N) management may need to be modified. Experiments were conducted in a high-yielding environment with total N applied up to 180 ​kg ​ha−1 and three application times to determine its effect on N uptake, grain yield and grain protein content of rice grown under aerobic (AR), delayed permanent water (DPW) and flooded (FD) conditions. Grain yield increased by 3.50–4.50 ​t ha−1 with total N application rate of 180 ​kg ​ha−1 in AR and 120 ​kg ​ha−1 in both DPW and FD. Maximum yield was about 10.5, 12.0 and 13.0 ​t ​ha−1 in AR, DPW and FD, respectively, and the difference was mostly reflected in the grain yield difference obtained under 0 N application. Apparent recovery of fertilised N and agronomic N use efficiency were similar between AR and FD, but DPW took up a higher proportion of N fertiliser applied before commencement of flooding and had slightly higher grain yield response to total N application up to 120 ​kg ​ha−1. It is concluded that the limitation for grain yield for rice grown in the AR condition was the crop's inability to take up N from the soil, rather than the inability to take up N fertiliser or to convert the N uptake to grain yield.

OsAAP15, an amino acid transporter in response to nitrogen concentration, mediates panicle branching and grain yield in rice

N is essential for plant architecture, particularly tillering. However, whether and how N mediates panicle branching and influences rice grain yield remains unclear. In order to identify genes and pathways associated with N-regulated panicle branching, we treated rice with different concentrations of N to determine the key genes by transcriptomic analysis and function verification. We measured panicle growth in response to N, and found that panicle branching benefits from 2 mM exogenous N, and 2–5 mM N is essential for vascular bundle, phloem, and xylem development in these branches. Interestingly, total N concentrations increased continuously with N 0–2 mM and decreased continuously with N 5–15 mM, whereas the concentrations of amino acids Tyr and Val increased continuously with N 0–15 mM in the panicle. Furthermore, N metabolism, phytohormone signal transduction, stress response, and photosynthesis pathways play important roles in response to nitrogen of regulating panicle branching. Altered expression of key N-response amino acid transporter gene OsAAP15 positively regulated panicle branching at low N concentrations, however, OsAAP15 negatively influenced it at high N concentrations. Overexpression of OsAAP15 in the field significantly increased primary and secondary branches, filled grain number, and grain yield by regulating the concentrations of amino acids Tyr and Val in the panicle. Taken together, OsAAP15, an amino acid transporter in response to nitrogen concentration, could mediate panicle branching and grain yield, and it may have applications in rice breeding to improve grain yield under extreme N concentrations.

Influence of Maturity Duration on Grain Yield of Rice under Direct-seeded Condition in the Tropics

Background: The optimum maturity duration for maximum grain yield of non-photosensitive rice (Oryza sativa) under direct-seeded condition in the tropics was studied. Information on such studies conducted using near-isogenic rice lines are lacking. Change in yield with maturity duration was explained using yield components. Methods: The experiment was conducted in the dry zone of Sri Lanka over two seasons namely dry and wet during 2021 and 2022. Non-photosensitive near-isogenic rice lines that are varying in maturity duration from 80 to 120 days but with 94.0% genetic uniformity were used as simple treatments in the study. Pre-germinated seeds of isogenic lines were direct-seeded in the experimental plots. Result: The most appropriate relationship between maturity duration and grain yield was cubic and the optimum maturity duration for the maximum grain yield was falling within 105 to 111 days in both dry and wet seasons under direct-seeded condition in non-photosensitive rice in the tropical climate. Number of panicles/m2 and number of spikelets/panicle influenced to change the grain yield of rice with the change in maturity duration.

Conventional and new breeding approaches to enhance grain yield in rice

From a ship-to-mouth existence at the time of its Independence, India became a food sufficient country due to the research and policy interventions during the green revolution era and in the last six decades. The country witnessed a phenomenal increase in the production and productivity of rice and wheat and presently the country is exporting significant quantities of rice. However, there are multiple challenges in ensuring food and nutritional security through rice in the coming decades including a rapidly changing climate and a plateauing of rice yields has been witnessed in the last two decades in many rice growing countries across the world including India. It is therefore imperative to enhance rice productivity and production through application of modern tools of science. This review traces the developments related to rice research and yield improvement over the last six decades and discusses about the conventional and modern approaches to enhance grain yield in rice. These approaches include pre-breeding, wide-hybridization, new plant type/ideotype breeding, heterosis breeding, marker and genomics-assisted breeding, haplotype-based breeding, transgenic breeding and genome editing.

Identification of superior haplotypes for CCD8 regulating tiller number and grain yield in rice

Rice is one of the major food crops of the world. In the present day of increasing population there is an urgent need to increase the rice grain production. Yield is a complex trait and is mainly orchestrated by plant architecture. In the present study, a diverse set of 100 accessions from the 3K RG panel were evaluated for Carotenoid cleavage dioxygenase 8 (CCD8) loci which plays a role in altering tiller number which ultimately governs the crop yield. A normal phenotypic distribution for total tiller numbers and number of productive tillers was observed for the set of 100 accessions used in the study. Five non synonymous SNPs were present for CCD8 loci for the 100 rice 3K accessions in this study. Haplotype analysis was carried out using five non synonymous SNPs to understand the genetic diversity of the population and of which two significant SNPs in the positions 31223371 and 31223383 grouped the accessions into two haplotype H1 and H2 with the allelic combination of GC and AT respectively. Haplotype group H1 with 89 accessions and H2 with 8 accessions were formed. Among the two haplotype groups, H2 had the maximum mean value for both tiller number and productive tiller number indicating the superiority of the H2 allelic combination over H1. Hence H2 is considered as a superior haplotype that can be potentially explored for allele mining and can be used in future crop improvement programs. Keywords: CCD8, tiller number, genetic diversity, haplotype.

LG5, a Novel Allele of EUI1, Regulates Grain Size and Flag Leaf Angle in Rice.

Grain size and flag leaf angle are two important traits that determining grain yield in rice. However, the mechanisms regulating these two traits remain largely unknown. In this study, a rice long grain 5 (lg5) mutant with a large flag leaf angle was identified, and map-based cloning revealed that a single base substitution followed by a 2 bp insertion in the LOC_Os05g40384 gene resulted in larger grains, a larger flag leaf angle, and higher plant height than the wild type. Sequence analysis revealed that lg5 is a novel allele of elongated uppermost internode-1 (EUI1), which encodes a cytochrome P450 protein. Functional complementation and overexpression tests showed that LG5 can rescue the bigger grain size and larger flag leaf angle in the Xiushui11 (XS) background. Knockdown of the LG5 transcription level by RNA interference resulted in elevated grain size and flag leaf angle in the Nipponbare (NIP) background. Morphological and cellular analyses suggested that LG5 regulated grain size and flag leaf angle by promoting cell expansion and cell proliferation. Our results provided new insight into the functions of EUI1 in rice, especially in regulating grain size and flag leaf angle, indicating a potential target for the improvement of rice breeding.

Influence of Nitrogen Application Rate on Stem Lodging Resistance Rice under Dry Cultivation

High grain yields of rice (Oryza sativa) under dry cultivation are primarily obtained through high levels of nitrogen (N) input. However, excessive inputs of N increase the risk of lodging. This study aimed to clarify the effect of N application rates on crop morphology, mechanical mechanisms of the stem, and chemical components in the basal stems of rice and their underlying mechanism in association with lodging resistance under dry cultivation. In this study, field experiments on rice were conducted under dry cultivation in early May to early October 2019 and 2020. Six rates of N applied at 0, 70, 140, 210, 280 and 350 kg ha−1 were set at a sowing rate of 150 kg ha−1 with Suijing 18 as the test material. The increased risk of lodging represented by lodging index (LI) and lodging rate with increasing N application was observed under both growing seasons. The plant height, basal internode length, particularly the second internode, and center of gravity height, which positively correlated with the LI, increased significantly with the increase in N application rates. In contrast, internode fullness and carbohydrate content of the basal second (S2) internode, which negatively correlated with LI, decreased significantly with increasing N application rates. A quadratic regression model between N application rates and grain yield showed that better grain yield could be achieved under an N application rate ranging from 210 to 228 kg ha−1. Therefore, the N application rate of (i.e., 210–228 kg N ha−1) could be recommended for the Suijing18 variety under dry cultivation in central Jilin Province for achieving high grain yield and great lodging resistance.

Elevated CO2 and temperature under future climate change increase severity of rice sheath blight.

Sheath blight (ShB), caused by Rhizoctonia solani, is one of the major threats to rice (Oryza sativa L.) production. However, it is not clear how the risk of rice ShB will respond to elevated CO2 and temperature under future climate change. Here, we conducted, field experiments of inoculated R. solani under combinations of two CO2 levels (ambient and enriched up to 590 μmol mol-1) and two temperature levels (ambient and increased by 2.0°C) in temperature by free-air CO2 enrichment (T-FACE) system for two cultivars (a susceptible cultivar, Lemont and a resistant cultivar, YSBR1). Results indicate that for the inoculation of plants with R. solani, the vertical length of ShB lesions for cv. Lemont was significantly longer than that for cv. YSBR1 under four CO2 and temperature treatments. The vertical length of ShB lesions was significantly increased by elevated temperature, but not by elevated CO2, for both cultivars. The vertical length of ShB lesions under the combination of elevated CO2 and elevated temperature was increased by 21-38% for cv. Lemont and by -1-6% for cv. YSBR1. A significant increase in MDA level was related to a significant increase in the vertical length of ShB lesions under the combination of elevated CO2 and elevated temperature. Elevated CO2 could not compensate for the negative effect of elevated temperature on yield of both cultivars under future climate change. Rice yield and biomass were further decreased by 2.0-2.5% and 2.9-4.2% by an increase in the severity of ShB under the combination of elevated CO2 and elevated temperature. Thus, reasonable agronomic management practices are required to improve both resistance to ShB disease and grain yield for rice under future climate change.

Comparison of potassium quantity-intensity relationships in tropical paddy soil under tillage and no-tillage systems after fifteen growing seasons

The information on the behaviour of potassium (K+) in tropical paddy rice soils, which is important for a better understanding of the plant availability of K+ is still very limited. We compared the quantity-intensity (Q/I) relationships for K+ under conventional tillage and no-tillage systems in tropical paddy fields in the absence and presence of K+ fertiliser in the addition of nitrogen. The results showed that the values of the activity ratio for K (ARK) and potential buffering capacities (PBCK) in the no-tillage rice field were respectively 16% and 33% higher than that in the conventional tillage field. With the addition of K fertiliser, the value of exchangeable K in equilibrium (ΔK0) in the no-tillage paddy field was 67.9% greater than that in the conventional tillage field. This indicates that K fertilisation is more efficient when applied on a no-tillage paddy field. When the K fertiliser was added (49.8 kg K/ha), the application of N fertiliser at the rate of 115 and 184 kg N/ha resulted in a higher ARK value than that at the rate of 46 kg N/ha. This suggests that the simultaneous application of K and N fertiliser was able to increase exchangeable K in the soil. The application of no-tillage increased of the dry grain yield of rice (about 10%) compared with the application of conventional tillage. Meanwhile, there were significant relationships between the rice yield with the ARK and ΔK0. Moreover, the ARK was significantly correlated with K-uptake.