Grain-filling strategies of wheat of contrasting grain sizes under various planting patterns and irrigation levels

In a study comparing grain filling and yield in a large-and a small-grain-size wheat cultivar under two planting patterns and two irrigation regimes,plastic-covered ridge and furrow planting with sprinkler irrigation increased grain filling and yield in both cultivars.The largest contributors to grain yield were an extended active grain-filling period in Shuangda 1 and an increased mean grain-filling rate in XN538.

FGW1, a protein containing DUF630 and DUF632 domains, regulates grain size and filling in Oryza sativa L.

Grain filling influences grain size and quality in cereal crops. The molecular mechanisms that regulate grain endosperm development remain elusive. In this study, we characterized a filling-defective and grain width mutant, fgw1, whose mutation increased rice seed width mainly via cell division and expansion in grains. Sucrose contents were higher but starch contents lower in the fgw1 mutant during the grainfilling stage, resulting in inferior endosperm of opaque, white appearance with loosely packed starch granules. Map-based cloning revealed that FGW1 encoded a protein containing DUF630/DUF632domains, localized in the plasma membrane with preferential expression in the panicle. RNA interference in FGW1 resulted in increased grain width and weight, whereas overexpression of FGW1 led to slightly narrower kernels and better grain filling. In a yeast two-hybrid assay, FGW1 interacted directly with the 14–3–3 protein GF14f, bimolecular fluorescence complementation verified that the site of interaction was the membrane, and the mutated FGW1 protein failed to interact with GF14f. The expression of GF14f was down-regulated in fgw1, and the activities of AGPase, StSase, and SuSase in the endosperm of fgw1increased similarly to those of a reported GF14f-RNAi. Transcriptome analysis indicated that FGW1 also regulates cellular processes and carbohydrate metabolism. Thus, FGW1 regulated grain formation via the GF14f pathway.

The causes and impacts for heat stress in spring maize during grain filling in the North China Plain--A review

High-temperature stress （HTS） at the grain-filling stage in spring maize （Zea mays L.） is the main obstacle to increasing productivity in the North China Plain （NCP）. To solve this problem, the physiological mechanisms of HTS, and its causes and impacts, must be understood. The HTS threshold of the duration and rate in grain filling, photosynthetic characteristics （e.g., the thermal stability of thylakoid membrane, chlorophyll and electron transfer, photosynthetic carbon assimilation）, water status （e.g., leaf water potential, turgor and leaf relative water content） and signal transduction in maize are reviewed. The HTS threshold for spring maize is highly desirable to be appraised to prevent damages by unfavorable temperatures during grain filling in this region. HTS has negative impacts on maize photosynthesis by damaging the stability of the thylakoid membrane structure and degrading chlorophyll, which reduces light energy absorption, transfer and photosynthetic carbon assimilation. In addition, photosynthesis can be deleteriously affected due to inhibited root growth under HTS in which plants decrease their water-absorbing capacity, leaf water potential, turgor, leaf relative water content, and stomatal conductance. Inhibited photosynthesis decrease the supply of photosynthates to the grain, leading to falling of kernel weight and even grain yield. However, maize does not respond passively to HTS. The plant transduces the abscisic acid （ABA） signal to express heat shock proteins （HSPs）, which are molecular chaperones that participate in protein refolding and degradation caused by HTS. HSPs stabilize target protein configurations and indirectly improve thylakoid membrane structure stability, light energy absorption and passing, electron transport, and fixed carbon assimilation, leading to improved photosynthesis. ABA also induces stomatal closure to maintain a good water status for photosynthesis. Based on understanding of such mechanisms, strategies for alleviating HTS at the grain-filling stage in spring maize are summarized. Eight strategies have the potential to improve the ability of spring maize to avoid or tolerate HTS in this study, e.g., adjusting sowing date to avoid HTS, breeding heat-tolerance varieties, and tillage methods, optimizing irrigation, heat acclimation, regulating chemicals, nutritional management, and planting geometric design to tolerate HTS. Based on the single technology breakthrough, a com- prehensive integrated technical system is needed to improve heat tolerance and increase the spring maize yield in the NCP.

Top-grain filling characteristics at an early stage of maize(Zea mays L.) with different nitrogen use efficiencies

Maize genotypes vary significantly in their nitrogen use efficiencies（NUEs）.Better understanding of early grain filling characteristics of maize is important,especially for maize with different NUEs.The objectives of this research were（i）to investigate the difference in apical kernel development of maize with different NUEs,（ii）to determine the reaction of apical kernel development to N application levels,and（iii）to evaluate the relationship between apical kernel development and grain yield（GY）for different genotypes of maize.Three maize hybrid varieties with different NUEs were cultivated in a field with different levels of N fertilizer arranged during two growing seasons.Kernel fresh weight（KFW）,volume（KV）and dry weight（KDW）of apical kernel were evaluated at an early grain filling stage.Ear characteristics,GY and its components were determined at maturity stage.Apical kernel of the high N and high efficiency（HN-HE）type（under low N,the yield is lower,and under higher N,the yield is higher）developed better under high N（N210 and N240,pure N of 210 and 240 kg ha^–1）than at low N（N120 and N140,pure N of 120 and 140 kg ha^–1）.The low N and high efficiency（LN-HE）type（under low N,the yield is higher,while under higher N,the yield is not significantly higher）developed better under low N than at high N.The double high efficiency（D-HE）type（for both low and high N,the yield is higher）performed well under both high and low N.Apical kernel reacted differently to the N supply.Apical kernel developed well at an early grain filling stage and resulted in a higher kernel number（KN）,kernel weight（KW）and GY with better ear characteristics at maturity.

Mapping QTL for Heat-Tolerance at Grain Filling Stage in Rice

A mapping population of 98 lines (backcross inbred lines, BILs) derived from a backcross of Nipponbare/Kasalath// Nipponbare was planted at two experimental sites, Nanjing and Nanchang, and treated with high and optimal temperature during grain filling, respectively. The grain weight heat susceptibility index [GWHSI= (grain weight at optimum temperature-grain weight at high temperature) / grain weight at optimum temperature × 100] was employed to evaluate the tolerance of rice to heat stress. A genetic linkage map with 245 RFLP markers and a mixed linear-model approach was used to detect quantitative trait loci (QTLs) and their main effects, epistatic interactions and QTL× environment interactions (Q×E). The threshold of LOD score=2.0 was used to detect the significance of association between marker and trait. A total of 3 QTLs controlling heat tolerance during grain filling were detected, on chromosomes 1, 4 and 7, with LOD scores of 8.16, 11.08 and 12.86, respectively, and they explained the phenotypic variance of 8.94, 17.25 and 13.50 %, correspondingly. The QTL located in the C1100-R1783 region of chromosome 4 showed no QTL× environment interaction and epistatic effect, suggesting that it could be stably expressed in different environments and genetic backgrounds, and thus it would be valuable in rice breeding for heat tolerance improvement. This QTL allele, derived from Kasalath reduced 3.31% of the grain weight loss under heat stress. One located between R1613-C970 on chromosome 1 and the other between C1226-R1440 on chromosome 7, with additive effect 2.38 and 2.92%, respectively. The tolerance alleles of both these QTLs were derived from Nipponbare. Both of these QTLs had significant QTL× environment interactions, and the latter was involved in epistatic interaction also. Eight pairs of epistatic effect QTLs were detected, one pair each on chromosomes 1,2,3, 5, 7, 8, 10 and 12. The results could be useful for elucidating the genetic mechanism of heat-tolerance and the development of new rice varieties with heat tolerance during grain filling phase.

Source-Sink and Grain-Filling Characteristics of Two-Line Hybrid Rice Yangliangyou 6

With two-line hybrid rice Yangliangyou 6 （YLY6） and Liangyoupeijiu （LYPJ） and three-line hybrid rice Shanyou 63 （SY63） as materials, the source, sink and flow characteristics in association with grain filling were investigated. The seed-setting rate, grain filling degree and grain yield of YLY6 and SY63 were significantly higher than those of LYPJ. The export and transformation percentages of the matter in culms and sheaths of YLY6 and SY63 were significantly higher than those of LYPJ. Activities of sucrose synthase, adenosine diphosphoglucose pyrophosphorylase, starch synthase and starch branching enzyme in grains were higher for YLY6 and SY63 than for LYPJ, and were very significantly correlated with maximum grain filling rate, mean grain filling rate, grain filling degree and grain weight. The spikelet number, grain yield and total sink load per area of vascular bundle and phloem of YLY6 and SY63 were significantly smaller than those of LYPJ, and the greater the load, the lower seed-setting rate and the poorer grain filling. The transportation rate per area phloem of YLY6 was greater than that of LYPJ or SY63. The results suggest that YLY6 possesses strong source, great sink activity and efficient flow, which lay a physiological base for its high seed-setting rate and good grain filling.

Grain-filling characteristics and yield differences of maize cultivars with contrasting nitrogen efficiencies

To investigate the effect of nitrogen management on the grain-filling characteristics and yield formation of maize cultivars with contrasting nitrogen efficiencies,and to identify differences in grain-filling characteristics and yield of maize cultivars in response to nitrogen management,a two-year field experiment was conducted in southwest China in2015–2016.The grain-filling rate and duration of the N-inefficient cultivar XY 508 were higher than those of the N-efficient cultivar ZH 311.The 100-kernel weight of XY 508 was significantly higher than that of ZH 311.The kernel number per ear of ZH 311 was significantly higher than that of XY 508,making the population filling rate of ZH 311 significantly higher than that of XY 508.The higher population filling rate of the N-efficient maize cultivar led to a significant yield advantage over the N-inefficient maize cultivar.Nitrogen management effectively improved maize grain yield,but the response of maize cultivars with contrasting nitrogen efficiencies to nitrogen management was inconsistent.A basal fertilizer ratio 60.43%with a topdressing ratio 39.57%effectively increased grainfilling rate,delayed the time to maximum filling rate,prolonged the active filling period and effective grain-filling time,increased the 100-kernel weight,and maintained higher kernels per ear,thereby improving the population filling rate and maximizing the yield advantage of the N-efficient cultivar.A 100%basal fertilizer ratio not only increased the number of kernels per ear,but also maintained high grain filling characteristics to obtain a higher 100-kernel weight and increased the population filling rate,leading to a high grain yield in the N-inefficient cultivar.Thus,the 100%basal fertilizer ratio partially compensated for the deficient grain yield of the N-inefficient cultivar.

Effects of Panicle Nitrogen Fertilization on Non-Structural Carbohydrate and Grain Filling in Indica Rice

Grain filling, a crucial stage of grain yield formation in rice, is usually affected by the panicle nitrogen （N） fertilization. Field and pot culture experiments were conducted to explore the underlying mechanisms of N effect. Two rice cultivars with high lodging resistance were grown in the field and pot. Four panicle N fertilization treatments were conducted in 2006 and repeated in 2007. The result showed that medium level of panicle N fertilization treatment （NM） enhanced the accumulation and translocation of non-structural carbohydrate （NSC） in the stem and sheath. Compared with non-nitrogen treatment （NO）, NM promoted the translocation of labeled ^13C from stem and sheath to grain. But, low level of panicle N fertilization treatment （NL） and high level of panicle N fertilization treatment （NH） showed the negative effect. The endosperm cell, grain length, and grain width of NM increased more quickly than that of NO from 4 to 10 d after anthesis. During the early period of grain filling, sucrose-phosphate synthase （EC 2.4.1.14, SPS） activity were significantly higher for the NM treatment than those of the NL and NH treatments. Sucrose synthase （EC 2.4.1.13, SuSase） activity in the grains was substantially enhanced by NM, with the duration of higher activity being longer than those of the other treatments. At maturing stage, NM significantly increased the filled grain number, the seed-setting rate, and the grain weight compared with NL and NH. The results suggest that NM have a positive effect on the activities of enzymes of physiological importance, thereby increasing the grain size and promoting grain filling.

The Effect of Plastic-Covered Ridge and Furrow Planting on the Grain Filling and Hormonal Changes of Winter Wheat

Although plastic-covered ridge and furrow planting（RF） has been reported to produce substantial increases in the grain weight of winter wheat,the underlying mechanism is not yet understood.The present study used two cultivars,Xinong 538 and Zhoumai 18,and RF and traditional flatten planting（TF,control） with the objective of investigating the effect of RF on wheat grain filling and the possible relationship of hormonal changes in the wheat grains under RF to grain filling.The results indicated that RF significantly increased the grain weight,although the effects on grain filling were different： RF significantly increased the grain-filling rate and grain weight of inferior grains,whereas RF had no significant effect on grainfilling rate and grain weight of superior grains.The final grain weight of inferior grains under RF was 39.1 and 50.7 mg for Xinong 538 and Zhoumai 18,respectively,3.6 and 3.4 mg higher than the values under TF.However,the final grain weight of superior grains under RF was only 0.6 and 0.8 mg higher than under TF for Xinong 538 and Zhoumai 18,respectively.RF significantly decreased the ethylene and gibberellic acid content in the inferior grains and increased the indole-3-acetic acid,abscisic acid and zeatin ＋ zeatin riboside content in the inferior grains;however,no significant difference between RF and TF was observed for the hormonal content in the superior grains.Based on these results,we concluded that RF significantly modulated hormonal changes in the inferior grains and,thus,affected the grain filling and grain weight of the inferior grains;in contrast,RF had no significant effect on grain filling,grain weight and hormonal changes in the superior wheat grains.

Effects of Early- and Late-Sowing on Starch Accumulation and Associated Enzyme Activities During Grain Filling Stage in Rice

The environmental temperature occurring during the grain filling stage is an important factoraffecting starch synthesis and accumulation in rice. We investigated starch accumulation, amylaseactivity and starch granule size distribution in two low-amylose japonica rice varieties, Nanjing 9108 andFujing 1606, grown in the field at different filling temperatures by manipulating sowing date. The two ricevarieties exhibited similar performances between two sowing dates. Total starch, amylose andamylopectin contents were lower at the early-filling stage of T1 treatment (Early-sowing) compared withthose at the same stage in T2 treatment (Late-sowing). In contrast, at the late-filling stage, when fieldtemperatures were generally decreasing, total starch and amylopectin contents in T1 were highercompared to those in T2. The ideal temperature for strong activity of ADP-glucose pyrophosphorylaseand soluble starch synthase was about 22℃. A higher temperature from the heading to maturity stagesin T1 increased the activities of starch branching enzyme and suppressed the activities of granule boundstarch synthetase and starch debranching enzyme. We found that rice produced larger-sized starchgranules under the T1 treatment. These results suggested that due to the early-sowing date, the hightemperature (30℃) occurring at the early-filling stage hindered starch synthesis and accumulation,however, the lower temperatures (22 ℃) at the late-filling stage allowed starch synthesis and accumulationto return to normal levels.

iTRAQ-based quantitative proteome characterization of wheat grains during filling stages

Using isobaric tags for relative and absolute quantification （iTRAQ） and associated analytic technologies, we have cataloged and compared 7 069 unique wheat proteins expressed during four substages of the filling stage. Among them, 859 are differentially expressed, showing at least a 2-fold difference in concentration across substages. Differentially expressed proteins （DEPs） includind high-molecular weight giutenin subunit （W5AIU1）, low-molecular weight glutenin subunit （QSW3V4）, gliadin/avenin-like seed protein （D2KFG9）, and avenin-like protein （W5DVL2）, all of which have previously been identified as important for nutritional quality and bread-making properties, and all of which were found to increase at the latter stages of development. We have applied statistical techniques to group the proteins into hierarchical clusters, and have consulted databases to infer functional and other relationships among the identified proteins.

Identification of microRNAs regulating grain filling of rice inferior spikelets in response to moderate soil drying post-anthesis

The grain filling of inferior spikelets is much less complete than that of superior spikelets in rice cultivars with large panicles and numerous spikelets and is promoted by moderate soil drying(MD)post-anthesis.A growing body of evidence has shown that microRNAs function in regulating grain development.However,little is known about the mechanism of microRNA control of grain filling of inferior spikelets in response to MD.In this study,grain filling of inferior spikelets was promoted by MD treatment in Nipponbare.Small-RNA profiling at the most active grain-filling stage was conducted in inferior spikelets under control(CK)and MD treatment.Of 521 known and 128 novel miRNAs,38 known and 9 novel miRNAs were differentially expressed between the CK and MD treatments.Target genes of differentially expressed miRNAs were involved in multiple developmental and signaling pathways associated with catalytic activity,carbohydrate metabolism,and other functions.Both miR1861 and miR397 were upregulated by MD,leading to a decrease in OsSBDCP1 and OsLAC,two negative regulators of SSIIIa activity and BR signaling,respectively.In contrast,miR1432 abundance was reduced by MD,resulting in upregulation of OsACOT and thus an elevated content of both ABA and IAA.These results suggest that both starch synthesis and phytohormone biosynthesis are regulated by differentially expressed miRNAs in inferior spikelets in response to MD treatment.Our results suggest the molecular mechanisms by which miRNAs regulate grain filling in inferior spikelets of rice under moderate soil drying,providing potential application in agriculture to increase rice yields by genetic approaches.

Study on the Relationship of the Characteristics of Vascular Bundles in the First Internode and Grain-filling of Heavy Panicle Type Hybrid Rice

The characteristics of vascular bundle in the first internode from top and grain-filling of heavy panicle type hybrid rice(HPTHR) were studied. The results were as follows: The HPTHR had more vascular bundles and a much bigger area of single vascular bundle, all vascular bundle, all phloem and all xylem in the first inter-node than Shanyou63. The vascular bundles had the similar load of spikelet number and sink capacity between the HPTHR and Shanyou63. The HPTHR had not only a larger sink but also normal grain-filling and sink-filling, high seed-setting rate and heavier panicle. Those characteristics of vascular bundle were the biological bases for the larger and heavier panicle of HPTHR. The results also indicated that the breeding model of HPTHR was an effective measure for the super high-yielding rice breeding.

The Endosperm-Specific Expression of YUCCA Genes Enhances Rice Grain Filling

Grain filling is a crucial process that affects yield in rice(Oryza sativa L.).Auxin biosynthesis and signaling are closely related to rice yield;therefore,it is important to understand the effects of auxin biosynthesis on rice grain filling to improve crop yield.In this study,we used physiological and molecular strategies to identify the roles of auxin in rice grain filling.Exogenous application of auxin(IAA)or auxin analogues(2,4-D)to young spikelets and flag leaves improved the seed-setting rate and yield per spike.Furthermore,real-time quantitative PCR assays confirmed that nine members of the OsYUCCA family of auxin biosynthetic genes were upregulated during grain filling,implication that auxin biosynthesis plays a major role in grain development.The specific expression of either Arabidopsis AtYUCCA1 or OsYUCCA2 in the endosperm or leaves resulted in increased expression of OsIAA genes and auxin content of seeds,as well as increased grain filling and seed-setting rate.This result establishes that the auxin content in grains and leaves is important for grain development.Our findings further highlight the potential applications for improving rice yield by elevating targeted gene expression in specific tissues.

Direct shear tests of coarse-grained fillings from high-speed railway subgrade in cold regions

In order to study the shear behavior of coarse-grained fillings taken from the subgrade bottom layer of a cold region high-speed railway,large scale direct shear tests were conducted with different normal pressures,water contents and temperatures.The results indicate that the relationship between shear displacement and shear stress changed from strain-softening at lower normal pressures to strain-hardening at higher normal pressures,in both unfrozen and frozen states.This phenomenon was mainly due to the shear dilatation deformation effect.The shear displacement-shear stress curves show similar stages.Besides,the shear stress rapidly increased and there was not an increment in the shear displacement during the initial stage of the shear process in the frozen state.In both the unfrozen or frozen states at the same water contents,the shear strength increased with increasing normal pressure.

Effects of Lodging at Different Filling Stages on Rice Yield and Grain Quality

The effects of lodging of rice plants from 20 d after full heading to maturity on yield and grain quality were investigated with a hybrid rice combination Liangyoupeijiu and a japonica rice cultivar CY-6. The results showed that, except for brown rice rate, almost all parameters for yield and grain quality including ratio of grain length to grain width, gelatinization temperature and gel consistency, were significantly influenced by lodging and thus deteriorated. Regression analysis suggested that, lodging one day earlier at the grain-filling stage could cause 2.66% to 2.71% of yield loss, 1.8 to 2.6 percentage points decrease of seed-setting rate, 0.26 to 0.32 g reduction of lO00-grain weight, 0.097 to 0. 155 percentage point decline of milled rice rate, as well as 0.13 to 0.27 percentage point increase of chalky grain rate, and 0.021 to 0.024 percentage point rise of protein content, and subsequently lower the eating quality.

Changes in Activities of the Key Enzymes Related to Starch Synthesis in Rice Grains During Grain Filling and Their Relationships with the Filling Rate and Cooking Quality

With 10 rice cultivars (lines) as materials, the changes in activities of adenosine diphosphoglucose pyrophosphorylase(ADPGPase), starch synthase (SSase) and starch branching enzyme (Q-enzyme) in the grains during grain filling, and theirrelationships with the filling rate, gel consistency (GC), alkali spreading value (ASV) and amylose content (AC) werestudied. The results showed that changes in activities of ADPGPase, SSase and Q-enzyme exhibited a single peak duringgrain filling, and the time of the activity peaks for the former two enzymes was earlier than that of the maximum grain-fillingrate (Tmax), and the time reaching the peak for Q-enzyme was synchronous with Tmax. The activities at early grain fillingstage, and the mean and maximum activities of each enzyme during grain filling period were positively and significantly orvery significantly correlated with the mean and maximum grain filling rate and starch content (mg grain-1) in the grains.Activities of ADPGPase at all grain filling stages and those of Q-enzyme at the early and mid filling stages were notsignificantly correlated the cooking quality (GC, ASV and AC). SSase activities at the early filling stage were significantlyand negatively correlated with GC and ASV, and positively correlated with AC. Activities of SSase at mid and late grainfilling stages and Q-enzyme at the late filling stage were significantly and positively correlated with GC and ASV, andnegatively correlated with AC. Spraying zeatin or abscisic acid at early grain filling stage could obviously regulate theactivities of ADPGPase, SSase and Q-enzyme in the grains.

Changes in Enzyme Activities Involved in Starch Synthesis and Hormone Concentrations in Superior and Inferior Spikelets and Their Association with Grain Filling of Super Rice

The changes in activities of key enzymes involved in sucrose-to-starch conversion and concentrations of hormones in superior and inferior spikelets of super rice were investigated and their association with grain filling was analyzed.Four super rice cultivars,Liangyoupeijiu,IIyou 084,Huaidao 9 and Wujing 15,and two high-yielding and elite check cultivars,Shanyou 63 and Yangfujing 8,were used.The activities of sucrose synthase （SuSase）,adenosine diphosphoglucose pyrophosphorylase （AGPase）,starch synthase （StSase） and starch branching enzyme （SBE）,and the concentrations of zeatin ＋ zeatin riboside （Z ＋ ZR）,indole-3-acetic acid （IAA） and abscisic acid （ABA） in superior and inferior spikelets were determined during the grain filling period and their relationships with grain filling rate were analyzed.Maximum grain filling rate,the time reaching the maximum grain-filling rate,mean grain filling rate and brown rice weight for superior spikelets showed a slight difference between the super and check rice cultivars,but were significantly lower in the super rice than in the check rice for inferior spikelets.Changes of enzyme activities and hormone concentrations in grains exhibited single peak curves during the grain filling period.The peak values and the mean activities of SuSase,AGPase,StSase and SBE were lower in inferior spikelets than in superior ones,as well as the peak values and the mean concentrations of Z ＋ ZR and IAA.However,the peak value and the mean concentration of ABA were significantly higher in inferior spikelets than in superior ones and greater in the super rice than in the check rice.The grain filling rate was positively and significantly correlated with the activities of SuSase,AGPase and StSase and the concentrations of Z ＋ ZR and IAA.The results suggested that the low activities of SuSase,AGPase and StSase and the low concentrations of Z ＋ ZR and IAA might be important physiological reasons for the slow grain filling rate and light grain weight of inferior spikelets in super rice.

Combined effect of shading time and nitrogen level on grain filling and grain quality in japonica super rice

There is limited information about the combined effect of shading time and nitrogen （N） on grain filling and quality of rice. Therefore, two japonica super rice cultivars, Nanjing 44 and Ningjing 3, were used to study the effect of shading time and N level on the characteristics of rice panicle and grain filling as well as the corresponding yield and quality. At a low N level （150 kg N ha^-1, 150N）, grain yield decreased （by 21.07-26.07%） under the treatment of 20 days of shading before heading （BH） compared with the no shading （NS） treatment. These decreases occurred because of shortened panicle length, decreased number of primary and secondary branches, as well as the grain number and weight per panicle. At 150N, in the treatment of 20 days of shading after heading （AH）, grain yield also decreased （by 9.46-10.60%） due to the lower grain weight per panicle. The interaction of shading and N level had a significant effect on the number of primary and secondary branches. A high level of N （300 kg N ha^-1, 300N） could offset the negative effect of shading on the number of secondary branches and grain weight per panicle, and consequently increased the grain yield in both shading treatments. In superior grains, compared with 150N NS, the time to reach 99% of the grain weight （T99） was shortened by 1.6 to 1.7 days, and the grain weight was decreased by 4.18-5.91% in 150N BH. In 150N AH, the grain weight was 13.39-13.92% lower than that in 150N NS due to the slow mean and the maximum grain-filling rate （GRmean and GRmax）. In inferior grains, grain weight and GRmean had a tendency of 150N NS〉150N BH〉150N AH. Under shaded conditions, 300N decreased the grain weight due to lower GReen both in superior and inferior grains. Compared with 150N NS, the milling and appearance qualities as well as eating and cooking quality were all decreased in 150N BH and 150N AH. Shading with the high level of 300N improved the milling quality and decreased the number of chalky rice kernels, but the eating and cooking quality was reduced with increased chalky area and overall chalkiness. Therefore, in the case of short term shading, appropriate N fertilizer could be used to improve the yield and milling quality of rice, but limited application of N fertilizer is recommended to achieve good eating and cooking quality of rice.

Relationship Between Lodging Resistance and Chemical Contents in Culms and Sheaths of Japonica Rice During Grain Filling

To understand the relationship between lodging resistance and chemical component contents in culms and leaf sheaths of rice, the physical strength and maximum bearing capacity of culm, and the contents and amounts of potassium （K） silicon （Si） and soluble sugars in culms and leaf sheaths were investigated using four japonica rice varieties with different lodging resistance characteristics during grain filling. There were significant differences in the total amounts of K, Si and soluble sugars in culms and leaf sheaths among the tested rice varieties. The difference in the total amount of Si was greater than that of K or soluble sugars. The physical strength and maximum bearing capacity of culm continuously decreased from heading to ripening, with a rapid decrease at the dough stage. However, the contents and total amounts of K and Si in culms and the Si content in leaf sheaths gradually increased and an accumulation of K and Si in culms was exhibited, whereas the content and total amount of K and the total amount of Si in leaf sheaths gradually decreased and an exportation of K and Si in leaf sheaths was presented. The physical strength was positively and significantly correlated with the total amounts of K and Si in culms during grain filling except that at the heading stage, the total amount of soluble sugars in culms at the heading and milky stages, the total amounts of Si and soluble sugars in leaf sheaths at the heading stage, the total amount of K in leaf sheaths at the heading and milky stages, and the maximum bearing capacity during grain filling. It is suggested that the lodging resistance of japonica rice would be improved by increasing the amount of soluble sugars in plants at the early filling stage, and enhancing the amount of Si in plants during grain filling through topdressing Si fertilizer at the early filling stage.