Super Rice Cultivars Research Articles

Root-Derived Short-Chain Suberin Diacids from Rice and Rape Seed in a Paddy Soil under Rice Cultivar Treatments.

Suberin-derived substituted fatty acids have been shown to be potential biomarkers for plant-derived carbon (C) in soils across ecosystems. Analyzing root derived suberin compounds bound in soil could help to understand the root input into a soil organic carbon pool. In this study, bound lipids were extracted and identified in root and topsoil samples. Short-chain suberin diacids were quantified under rice (Oryza sativa L.) and rape (Brassica campestris) rotations with different cultivar combinations in a Chinese rice paddy. After removal of free lipids with sequential extraction, the residual bound lipids were obtained with saponification and derivatization before analysis using gas chromatography–mass spectrometry (GC-MS). Diacids C16 and C18 in bound lipids were detected both in rice and rape root samples, while diacids C20 and C22 were detected only in rape root samples. Accordingly, diacids were quantified in both rhizosphere and bulk soil (0–15 cm). The amount of total root-derived diacids in bulk soil varied in a range of 5.6–9.6 mg/kg across growth stages and crop seasons. After one year-round rice-rape rotation, root-derived suberin diacids were maintained at a level of 7–9 mg/kg in bulk soil; this was higher under a super rice cultivar LY than under a hybrid cultivar IIY. While concentrations of the analyzed diacids were generally higher in rhizosphere than in bulk soil, the total diacid (DA) concentration was higher at the time of rape harvest than at rice harvest, suggesting that rape roots made a major contribution to the preservation of diacids in the paddy. Moreover, the net change in the concentration and the ratios of C16:0 DA to C18:1 DA, and of C16:0 DA to C18:0 DA, over a whole growing season, were greater under LY than under IIY, though there was no difference between cultivars within a single growth stage. Overall, total concentration of root-derived suberin diacids was found to be positively correlated to soil organic carbon concentration both for bulk soil and rhizosphere. However, the turnover and preservation of the root suberin biomolecules with soil property and field conditions deserve further field studies.

Spikelet-specific variation in ethylene production and constitutive expression of ethylene receptors and signal transducers during grain filling of compact- and lax-panicle rice (Oryza sativa) cultivars

Grain yields in modern super rice cultivars do not always meet the expectations because many spikelets are located on secondary branches in closely packed homogeneous distribution in these plants, and they do not fill properly. The factors limiting grain filling of such spikelets, especially in the lower panicle branches, are elusive. Two long-duration rice cultivars differing in panicle density, Mahalaxmi (compact) and Upahar (lax), were cultivated in an open field plot. Grain filling, ethylene production and constitutive expression of ethylene receptors and ethylene signal transducers in apical and basal spikelets of the panicle were compared during the early post-anthesis stage, which is the most critical period for grain development. In another experiment, a similar assessment was made for the medium-duration cultivars compact-panicle OR-1918 and lax-panicle Lalat. Grain weight of the apical spikelets was always higher than that of the basal spikelets. This gradient of grain weight was wide in the compact-panicle cultivars and narrow in the lax-panicle cultivars. Compared to apical spikelets, the basal spikelets produced more ethylene at anthesis and retained the capacity for post-anthesis expression of ethylene receptors and ethylene signal transducers longer. High ethylene production enhanced the expression of the RSR1 gene, but reduced expression of the GBSS1 gene. Ethylene inhibited the partitioning of assimilates of developing grains resulting in low starch biosynthesis and high accumulation of soluble carbohydrates. It is concluded that an increase in grain/spikelet density in rice panicles reduces apical dominance to the detriment of grain filling by production of ethylene and/or enhanced perception of the ethylene signal. Ethylene could be a second messenger for apical dominance in grain filling. The manipulation of the ethylene signal would possibly improve rice grain yield.

Effect of genetic improvement of grain yield and nitrogen efficiency of mid‐seasonindicarice cultivars

AbstractGenetic improvement (GI) of mid‐seasonindicarice (Oryza sativaL.) in China has been experienced four typical plant types during the past several decades,i.e., early tall cultivars (ET), dwarf cultivars (DC), semi‐dwarf cultivars (SDC) and super rice cultivars (SR). However, little is known about the changes in fertilizer nitrogen (N) efficiency and their relationships with grain yield during the GI. With 12 representative mid‐seasonindicacultivars of the four types during GI, the effects of GI on grain yield and nitrogen efficiency were investigated. The results show that GI significantly increased grain yield and agronomic efficiency (AE) of N fertilizer but had no significant effect on recovery efficiency (RE) of N fertilizer. The low percentage of filled grains in modern SR limited its yield potential and the further increase in AE. GI decreased the N uptake from heading to maturity, leading to lower RE in modern rice cultivars. The rapid decline of the activities of root oxidation and nitrate reductase in SR during grain filling might be the physiological reasons for the lower percentage of filled grains and lower N uptake from heading to maturity.

Grain Yield and Nitrogen Use Efficiency of Mid-season Indica Rice Cultivars Applied at Different Decades

Improvement in rice cultivars plays an important role in increasing grain yield. However, little is known about the relationship between yield and nitrogen use efficiency in mid-season indica rice cultivar improvement process. In this study, 12 typical cultivars(including hybrid combinations) applied in the production in Jiangsu Province during the last 70 years were used, and classified into four types of 1940–1950s, 1960–1970s, 1980–1990s, and after 2000(super rice) according to their application times. Three treatments of zero N(0N), 210 kg ha–1 N(MN) and 300 kg ha–1 N(HN) were designed. The results showed that grain yield and nitrogen use efficiency were progressively increased with the improvement of cultivars under each nitrogen rate. The super rice cultivars had a higher biomass and nitrogen accumulation, higher activities of root oxidation and nitrogen metabolic enzyme and higher leaf photosynthetic rate resulting in higher grain yield and nitrogen use efficiency when compared with any other types of cultivars. The root oxidation activity and photosynthetic characteristics of super rice were the peak at the heading stage, but sharp declined from heading to maturity, which could account for an important physiological reason for a lower filled-grain percentage of super rice. It would be an important approach to further increase grain yield of super rice through increasing root activity and leaf photosynthetic rate during grain filling.

Changes in Grain Yield and Root Morphology and Physiology of Mid-Season Rice in the Yangtze River Basin of China During the Last 60 Years

The genetic improvement (GI) plays an important role in yield increase in rice in the Yangtze River Basin of China, and rice roots might have a crucial function during the GI. However, little is known what changes in root physiology and morphology were during the GI in this area and how they were related with grain yield. In this study, 24 typical mid-season rice cultivars (including hybrid combinations) applied in the area during the last 60 years were grown in the field, and they were classified into six types according to their application decades in which the cultivars were predominantly used. Changes in morphological and physiological traits of roots and their relationships with grain yield during the GI were investigated. Results showed that grain yield was significantly increased. Increase in grain yield was attributed mainly to the increase in total number of spikelets, which resulted mainly from a large panicle. The root dry weight, root length, root diameter, root oxidation activity, total absorbing surface area and active absorbing surface area of roots were also increased with the GI. Regression analysis showed that the root dry weight, root length, root diameter, root oxidation activity, total absorbing surface area and active absorbing surface area of roots were very significantly and positively correlated with grain yield. The results suggest that the GI improves root morph-physiological traits which benefits shoot growth, leading to a higher grain yield for the modern cultivars, especially for super rice cultivars.

Biomass accumulation and partitioning of newly developed Green Super Rice (GSR) cultivars under drought stress during the reproductive stage

Drought is a major abiotic threat in rice production; thus, there is a need to develop adaptable rice varieties that can withstand drought stress and still produce high yield in non-stressed environments. Green Super Rice (GSR) cultivars address this issue. These cultivars are bred through an innovative introgression breeding strategy that requires less irrigation water and chemical inputs without compromising grain quality and yield. This study verified the physiological efficiency and performance of newly developed GSR cultivars that previously showed favorable response to drought during advanced yield trials. Five drought-tolerant GSR cultivars and two checks were subjected to continuously flooded (CF) and drought-stressed environments during the dry seasons of 2011 and 2012 at the International Rice Research Institute (IRRI) experimental farms in Los Baños, Philippines. The cultivars’ ability to allocate assimilates and accumulate biomass under drought stress during the reproductive stage was verified. Leaf area index (LAI), biomass dry weight, and panicle yield were measured at the panicle initiation (PI), flowering (FL), and physiological maturity (PM) of the sample cultivars. All the cultivars performed satisfactorily in the CF environment with grain yield ranging from 5 to 11.5tonsha−1. Water stress during the reproductive stage significantly reduced grain yield by 75–88% in the moderate drought (soil water tension between 100 and 300kPa in upper 15cm soil layer) and 77–96% in the severe drought (soil water tension >300kPa in upper 15cm soil layer) experiments. The shortened reproductive duration mainly contributed to the significant reduction in yield under drought stress. Two GSR cultivars, GSR IR1-5-S10-D1-D1 and IR83142-B-19-B, responded well in severe drought environments, with grain yield almost similar to the drought check (1.79tonsha−1). Under moderate drought stress, there was a relative yield advantage of 25% and 40% for the two GSR cultivars over the drought check, respectively. Yield advantage across environments, varying from fully irrigated to drought-stressed, was 31–36%. These two GSR cultivars were effective in mobilizing stored carbohydrates from the vegetative organs to the panicles and not shortening the duration from flowering to maturity, to allow all reserved carbohydrates be allocated to storage organs as a mechanism to cope with drought stress. Lower leaf area index (LAI), which allowed balanced biomass accumulation and lower transpiration, without a significant decrease in grain filling duration, was another drought-coping strategy. These physiological responses and characteristics apparently enabled the GSR cultivars to withstand drought stress; these are key indicators for varietal selection in drought-prone environments, particularly in severe drought stress in the reproductive stage. Despite the poor ability of some cultivars to cope with severe drought, three out of five selected GSR cultivars produced grain yield (2.0–2.9tonsha−1) that was the same or higher than the drought check in moderate drought stress. The introgression breeding technique applied in the newly developed drought-tolerant cultivars through the GSR breeding strategy was found to be effective. It could produce high yields in both CF and water-limited environments, and thus, it could serve as a model for other breeding programs to adopt.

Effects of Nitrogen Application Rate and Ratio on Lodging Resistance of Super Rice with Different Genotypes

The objective of this study was to determine the morphology mechanism of nitrogen (N) fertilizer rates and ratio on lodging resistance through analying its effects among lodging index (LI), lodging-related morphological traits and physical strength in basal internodes by comparing japonica and indica super rice cultivars. Field experiments, with three nitrogen levels (0, 150 and 300 kg ha−1) and two ratios of basal to topdressing (8:2 and 5:5) with two super rice cultivars (Yliangyou 2 and Wuyunjing 23), were conducted in the Baolin Farm, Danyang Country, Jiangsu Province, China, in 2011 and 2012. Effects of N fertilizer rates and ratios on morphology of whole plant, morphology traits in basal internodes and culm's physical strength parameters were investigated at 20 d after full heading stage. LI of Yliangyou 2 was significant greater than that of Wuyunjing 23 due to larger bending moment by whole plant (WP) with higher plant height and gravity center height. With higher volume of N fertilizer, LI of two super rice cultivars was increased conspicuously. However, no significant effect was detected with increase of panicle fertilizer ratio. The size of breaking strength (M) in basal internodes was the key factor determining LI among N fertilizer treatments. Correlation analysis revealed that M value was positively related bending stress (BS) of Wuyunjing 23 and section modulus (Z) of Yliangyou 2, respectively. The higher N fertilizer levels induced reduction of BS of Wuyunjing 23 due to weak culm and leaf sheath plumpness status and reduced Z of Yliangyou 2 owning to small diameter and culm wall thickness, consequently, influencing their M indirectly. These results suggested that breaking strength was the key factor influencing LI with increase of N fertilizer levels. However, the lodging-related morphology mechanism was different with genotypes. Culm wall thickness and diameter in basal internodes of indica super rice and culm and leaf sheath plumpness status of japonica super rice influenced breaking strength, as well as lodging index, respectively.

Effects of Alternate Wetting and Drying Irrigation during Grain Filling on the Seed-Setting Rate and Grain Weight of Two Super Rice Cultivars

Effects of Alternate Wetting and Drying Irrigation during Grain Filling on the Seed-Setting Rate and Grain Weight of Two Super Rice Cultivars

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.

Dynamic Characteristics of Matter Population in Two Super Hybrid Rice Cultivars

In order to find foundations of high-yield cultivation in super hybrid rice(SHR), we modeled on dynamics of population indices. A field experiment with two super hybrid rice cultivars(Zhunliangyou 527, Q you 6) and control(II you 838) was conducted in 2011 and 2012, and dry matter accumulation(DMA) and leaf area index(LAI) were measured. The dynamic equations of DMA and relative leaf area index(RLAI) were established and the dynamic characteristics of crop growth rate(CGR),relative growth rate(RGR), leaf area duration(LAD), net assimilation rate(NAR), and specific leaf area(LAR) were analyzed based on the equations. The DMA and its proportion to the total biomass at rapid growth stage were significantly higher than those of Control. In the process of time after transplanting, the tendency of CGR was expressed in a single peak curve, and CGR of two SHR was higher than that of control in rapid growth stage. The RGR of Zhunliangyou 527 was higher than that of control from 23d after transplanting to mature period. As compared with the RGR of control, the RGR of Q you 6 was lower before 43 d after transplanting, higher from 43 d to 113 d after transplanting, and not much difference from 113 d after transplanting to maturity. A significant correlation was observed between gross LAD and LAD at rapid growth stage, and also between gross LAD and duration of LAI at rapid growth stage. Compared with Control, the RGR of SHR showed faster increasing and decreasing, and its peak value was higher. A single peak curve was available for the dynamic changes of NAR with its most high value from 43 d to 53 d after transplanting. The LAR of two SHR decreased fast from 23 d to 43 d after transplanting, moderately from 73 d to mature stage, and slowly from 43 d to 73 d after transplanting stage. The LAR of two SHR was higher in rapid growth stage than that of control.

Performance in Grain Yield and Physiological Traits of Rice in the Yangtze River Basin of China During the Last 60 yr

Knowledge on the performance in grain yield and physiological traits is essential to understand the main yield-limiting factor and make strategies for breeding and crop management in rice (Oryza sativa L.). This study investigated the changes in grain yield and associated physiological traits of rice in the Yangtze River Basin of China during the last 60 yr. Thirteen mid-season indica and 12 japonica rice cultivars that were popularly used were grown in the field in 2008 and 2009. The grain yield and yield components, biomass, leaf area, leaf photosynthesis, root oxidation activity, and harvest index were examined. The results showed that grain yield and grain yield per day have progressively increased during the years and such increases are mainly attributed to the expanded sink size as a result of more spikelets per panicle, especially for the case of super rice. Both biomass and harvest index were increased with the improvement of cultivars. Increase in biomass for modern rice cultivars was associated with an enhancement of leaf area and photosynthesis, root dry weight, and root oxidation activity, although the indica super rice cultivars showed a lower leaf photosynthetic rate and root oxidation activity than the semi-dwarf cultivars during the grain filling period. Both indica and japonica super rice cultivars exhibited a low percentage of filled grains, which may limit their great yield potential. All the data suggested that grain yield have been substantially improved during the 60 yr of rice breeding in the Yangtze River Basin. Expanded sink size, increased dry matter production and harvest index, and enhanced leaf area and photosynthesis, root dry weight, and root oxidation activity contribute to the improvement in grain yield. Increase in filling efficiency could realize the great yield potential in super rice.

Influence of Planting Methods on Root System Morphological and Physiologi-cal Characteristics of Super Rice under High-yielding Cultivation Condition

A field experiment was conducted to compare the root system morphological and physiological characteristics of two super rice cultivars(Huaidao9 and Xudao3) using three planting methods,i.e.,precision artificial transplanting with dry nursery middle and strong seedlings(AT),mechanical transplanting with small seedlings(MT) and direct seeding(DS).Results were as follows.(1) Yields of super rice under different planting methods were very significantly different.Compared with AT,yields of MT and DS reduced by 5.05% and 13.68%,respectively.(2) The population root number was DSMTAT,while the difference was decreasing with the growing process.Total population root length was shown to be DSMTAT at jointing and MTATDS at heading and maturity.Root number per stem showed no significant difference among different planting methods,and total root length per stem was ATMTDS with generally significant difference.Length of single root was of no significant difference be-tween AT and MT,though both were significantly higher than DS.As for root diameter,the result was ATMTDS and the dif-ference among different planting methods was significant.(3) Population root dry weight showed no significant difference be-tween MT and DS at jointing,that both had the extremely significantly higher value than AT.There was no significant difference among different planting methods at heading,but when at maturity it was ATMTDS and the difference was very significant.As for decreasing rate of population root dry weight after heading,it was DSMTAT with significant difference.Root dry weight per stem was ATMTDS through jointing,heading and maturity,and the difference among different planting methods was mostly very significant.Decreasing rate of root dry weight per stem after heading displayed no significant difference between DS and MT,but both of them had the significantly higher value than AT.Shoot dry weight reduced in order for AT,MT,and DS,but root-shoot ratio increased in the same order.(4) Compared with AT,roots of MT and DS were mainly distributed within the soil layer of 0-10 cm underground,especially for DS,the root proportion in 0-5 cm soil layer could sum up to 65%.Ratio of root dry weight in 0-5 cm soil layer to total root weight increased in order for AT,MT,and DS,while the ratios in the soil layers of 5-10 cm,10-15 cm and 15 cm reduced in that order.(5) Population root absorption area showed no significant difference among dif-ferent planting methods at jointing,performed as ATMTDS at heading with very significant difference,and,at maturity,showed no significant difference between MT and AT,both of which had the very significantly higher value than DS.Root ab-sorption area per stem was of no significant difference between AT and MT at jointing and maturity while both had the very sig-nificantly higher value than DS,and was ATMTDS at heading with very significant difference.(6) Population root bleeding intensity after heading increased in order for AT,MT,and DS,but root bleeding intensity per stem reduced in the same order.The results suggested that planting methods have significant influence on root morphological and physiological characteristics of super rice.The different single root length and diameter and the difference in root distribution pattern in soil layer are two most signifi-cant characteristics of rice roots under different planting methods.Compared with AT and MT,the DS method develops roots of shallower distribution,smaller single root length and diameter and higher population root number,though with shorter total root length per stem,lower root dry weight,and less absorption area and bleeding intensity after heading.Compared with AT,root diameter of MT was smaller,distribution shallower,after heading root dry weight of plant population and of single stem both lower and declining faster,and total root length and bleeding intensity per stem inferior.

Effects of Soil Fertility and Nitrogen Application Rates on Super Rice Yield, Quality, and Nitrogen Use Efficiency

Xudao 3 is a japonica super rice cultivar widely used in mid-maturing rice production in the North Huai River area. Using this cultivar, the effects of nitrogen (N) application (0, 148.5, 223.5, 297.0, 372.0, and 445.5 kg ha 1) on yield, yield components, grain quality, and N use efficiency were studied under different soil fertility levels. The yield of Xudao 3 in response to soil basic fertility showed the trend of high fertility medium fertility low fertility. The optimal N application rates for the highest yield were 260.8 kg ha 1 in the high-fertility field, 290.5 kg ha 1 in the medium-fertility field, and 345.5 kg ha 1 in the low-fertility field. There were significant quadratic relationships between apparent N recovery efficiency (ANRE) and N application; and the optimal N application rates for the highest ANRE were 268.6 kg ha 1 in the high-fertility field, 293.4 kg ha 1 in the medium-fertility field, and 335.2 kg ha 1 in the low-fertility field. Optimization of soil fertility was able to improve nutritional, processing, and cooking-eating qualities, and N application rate should vary with the soil basic fertility. In a comprehensive consideration of high-yield, good quality, and high N use efficiency, we suggested that the reasonable N application rates were 240-270 kg ha 1 for soil with high fertility, 285-315 kg ha 1 for soil with medium fertility, and 330-360 kg ha 1 for soil with low fertility in super rice production in the North Huai River area.

Influence of Planting Methods on Grain-filling Properties of Super Rice

To explore grain-filling properties of high-yielding rice under different planting methods,we studied the grain-filling processes of superior and inferior grains of two super rice cultivars(Huaidao 9 and III you 98) with Richards equation W=A/(1+Be-Kt)1/N and three planting methods,i.e.precision artificial transplanting with dry nursery middle and strong seedlings(ATR),mechanical transplanting with small seedlings(MTR) and direct seeding(DSR).The results were as follows:(1) The super rice yields under different planting methods were significantly different,ATR was the highest,followed by the MTR,and the lowest was the DSR.Compared with ATR and MTR,the 1000-grain weight and seed-setting rate of DSR were significantly lower,but the changes between ATR and MTR were different due to different types of cultivar.(2) The grain-filling processes of superior and inferior grains of super rice under different planting methods were obviously asynchronous type.The time reaching the maximum grain-filling rate(Tmax) of superior grains was early,maximum grain-filling rate(GRmax),mean grain-filling rate(GRmean),the final weight of a kernel(A) and initial grain-filling potential(R0) were significantly greater than those of inferior grains.However,the active grain-filling period(D) and effective grain-filling time(T99) of the superior grains were significantly less than those of inferior grains.(3) Compared with ATR and MTR,the GRmax and GRmean of superior grains of DSR were significantly lower,Tmax was obviously delayed,D and T99 significantly increased.The GRmax and GRmean of inferior grains of MTR were the highest,and ATR was slightly lower than DSR.For Tmax,DSR was the earliest,MTR was the second,and the latest was ATR.D and T99 reduced in order for ATR,MTR,and DSR.(4) For grain-filling characteristics of different stages,the maximum of mean grain-filling rate and contribution rate was present at the middle stage,and the contribution rates of superior and inferior grains were up to 60.53% and 50.78%,respectively.The grain-filling days,mean grain-filling rate and contribution rate of the early,middle and late stages among different planting methods were different due to grain positions.(5) 1000-grain weight was positively correlated with maximum grain-filling rate,mean grain-filling rate and active grain-filling period of superior and inferior grains,and the correlations with maximum grain-filling rate and mean grain-filling rate of inferior grains were significant.Seed-setting rate had in a degree of positive or negative correlations with the grain-filling parameters of the superior and inferior grains,however,except the active grain-filling period of superior grains,all of the correlations were not significant.The results suggested that planting methods have significant influence on grain-filling properties of super rice.Although the grain-filling processes are all asynchronous types,the grain-filling parameters such as maximum grain-filling rate and the time reaching the maximum grain-filling rate of superior and inferior grains have great difference among different planting methods.It would play an important role in improving 1000-grain weight and grain-filling rate,especially the grain-filling rate of inferior grains under the conditions maintaining the final weight of a kernel and seed-setting rate stable.

Effects of Non-flooded Mulching Cultivation on the Yield and Quality of Rice

Plastic film or straw mulching cultivation under non-flooded condition has been considered as a new water-saving technique in rice production. This study aimed to investigate the yield performance in terms of quality and quantity under such practices. Two super rice cultivars, Wujing 15 (a japonica cultivar) and Liangyoupeijiu (an indica hybrid cultivar) were used with four cultivation treatments from transplanting to maturity: traditional flooding as control (TF), no-flooded plastic film mulching (PM), non-flooded wheat straw mulching (SM), and no flooding and no mulching (NM). Compared with that under TF, grain yield showed some reduction under all the non-flooded cultivations but differed largely among the treatments. The reduction in yield was 38.7-46.5% under NM, 9.8-17.4% under PM, and 1.7-7.0% under SM. The difference in grain yield was significant between NM and TF or between PM and TF, and was not significant between SM and TF. SM significantly improved milling, appearance, and cooking qualities, whereas PM or NM decreased these qualities. SM also significantly increased the peak visco- sity and breakdown value, and reduced setback value, and PM or NM had the opposite effect. The two cultivars showed similar trends in quality and quantity of rice yield. SM significantly increased root oxidation activity, leaf photosynthetic rate, and activities of key enzymes in sucrose-to-starch conversion in grains during the grain filling period, whereas PM and NM significantly reduced these parameters. The results indicate that SM could not only maintain a high grain yield, but also improve quality of rice. Increases in leaf photosynthetic rate, root activity, and activities of the key enzymes involved in the sucrose-starch metabolic pathway in grains under SM contributed to a higher grain yield and better quality of rice.

Changes in Grain Yield and Morphological and Physiological Characteristics During 60-Year Evolution of Japonica Rice Cultivars in Jiangsu

Twelve typical japonica cultivars from rice ( Oryza sativa L.) production in Jiangsu Province, China since the 1950s were chosen to study the evolution of plant type and grain yield. Cultivars in each decade were represented with 2 cultivars and investigated with morphological traits, source-sink related traits, grain yield, and yield components. During the cultivar alternation, grain yield was progressively increased with the main attribution of total number of spikelets, which resulted from large panicle. From the 1950s to the 1970s, the percentage of filled grains of cultivars showed an increase trend. However, it was declined since the 1980s, especially in super rice developed after the 1990s. There was no significant difference in 1000-grain weight among cultivars from different decades. Biomass and harvest index were improved with cultivar replacement, especially biomass after heading. Besides, root dry weight, root-to-shoot ratio, root oxidation activity, and photosynthetic rate of leaves at main growth stages were enhanced significantly, except that root oxidation activity and photosynthetic rate of leaves were reduced rapidly in super rice during grain filing. In the recent 60 years, japonica rice cultivars in Jiangsu Province have been obviously improved in total leaf area, effective leaf area, high-effective leaf area, ratio of total spikelet number to leaf area at heading stage, panicle length, and number of primary and secondary panicle branches. Plant height was shortened from the 1950s to the 1990s, but increased to approximately 120 cm in super rice that were mainly planted since 2000. Leaf angle of the top 3 leaves at heading stage was significantly reduced with the improvement of rice cultivar. These results indicate that agronomical traits and physiological characteristics of japonica cultivars in Jiangsu Province have been improved during the cultivar evolution, and low percentage of filled grain is a critical restraint for super rice cultivar to access its grain yield potential.

Post-Anthesis Changes in Concentrations of Polyamines in Superior and Inferior Spikelets and Their Relation with Grain Filling of Super Rice

Success in super rice breeding has been considered a great progress in rice production in China. However, many un-filled inferior spikelets limit the realization of great yield. As polyamines have been frequently described as endogenous plant growth regulators or intracellular messengers mediating physiological processes, this study investigated whether and how poly-amines are involved in the regulating post-anthesis development of rice spikelets. Four super rice cultivars, Liangyoupeijiu and II you 084 (indica hybrids), Huaidao 9 and Wujing 15 (japonica), and two high-yielding check cultivars, Shanyou 63 (indica hybrid) and Yangfujing 8 (japonica), were field grown. Concentrations of putrescine (Put), spermidine (Spd) and spermine (Spm) in both inferior and superior spikelets during the grain filling period and grain filling rate were determined. The relationship between polyamine concentrations and grain filling rate were analyzed, and chemical regulators were applied to verify the roles of poly-amines in grain filling. The results showed that the maximum grain filling rate, mean grain filling rate, and brown rice weight for superior spikelets showed small difference between the super rice and check rice, but those of inferior spikelets were significantly lower for super rice than for check rice cultivars. Changes in concentrations of polyamines in grains exhibited single peak during the grain filling period. The peak and mean concentrations of Put were greater in inferior than in superior spikelets. The peak and mean concentrations of Spd and Spm were greater in the superior than in the inferior, and greater in the check rice than in the su-per rice. The mean grain filling rate and brown rice weight were negatively and very significantly correlated with the Put concen-trations, and positively and very significantly correlated with Spd and Spm concentrations, Spd/Put, and Spm/Put. Application of Spd or Spm to panicle at the early grain filling stage significantly enhanced activities of sucrose synthetase, adenine di-phosphoglucose pyrophosphorylase, and soluble starch synthetase in inferior spikelets, and significantly increased grain filling rate, seed setting rate and grain weight of inferior spikelets. Application of Put or methylglyoxal-bis (guanylhydrazone) (MGBG, an inhibitor of S-adenosyl-L-methionine decarboxylase) exhibited an opposite effect. The results suggest that polyamines play a role in regulating grain filling. Low concentrations of Spd and Spm and low Spd/Put and Spm/Put may be an important physiological reason for the small grain filling rate and low grain weight of inferior spikelets in super rice.

Coordination between Source and Sink in Super Early and Late Rice

In order to clarify the super higher yield mechanism of super early and late rice,we studied the source and sink characteristics under field conditions.Compared with non-super rice cultivars(control cultivar),the total sink capacity,ratio of grain-leaf area and ratio of grain-vascular bundle of super rice were higher,and positively and significantly correlated with grain yield.During filling stage,the ratio of source increase to sink of super early and late rice was slightly higher than that of control cultivars,but in the mid-late filling stage(10-25 d after heading) of early rice and the early filling stage(0-10 d after heading) of late rice,the ratio was significantly larger than that of control cultivars.The initial grain-filling rate and mean grain-filling rate of super early,and late rice were higher than those of control cultivars,and positively and significantly correlated with filled grain rate and yield,respectively.The degradation rates of root activity of super early and late rice after heading were lower than those of control cultivars,while the temperature depression(difference between air temperature and leaf temperature) was higher than that of control cultivars except early rice Zhuliangyou 819 and late rice Ganxin 688.The degradation rate of root activity and the temperature depression were negatively and positively,correlated with grain yield,respectively.The results suggested that larger total sink capacity and better coordination between source and sink should be the important mechanism for super higher yield in super early and late rice cultivars.

Post-Anthesis Changes in Concentration of Polyamine in Superior and Inferior Spikelets and Their Relationship with Grain Filling of Super Rice

To reveal the physiological role of polyamines and the mechanism involved in grain-filling of rice ( Oryza sativa L.) superior and inferior spikelets, the relationship between grain-filling rate and polyamine concentrations was analyzed and verified using 4 super rice cultivars and 2 high-yielding cultivars (controls). Compared with the controls, super rice had similar maximum grain-filling rate, mean grain-filling rate, and brown rice weight in superior spikelets and significantly lower values in inferior spikelets. The concentrations of putrescine (Put), spermidine (Spd), and spermine (Spm) varied in single-peak curves in both inferior and superior spikelets during grain-filling period. The peak and mean concentrations of Put were greater in inferior spikelets than in superior spikelets. However, the peak and mean concentrations of Spd and Spm were greater in superior spikelets than in inferior spikelets. The control cultivars had higher concentrations of polyamines than super rice. The mean grain-filling rate and brown rice weight were negatively correlated with Put concentration, and positively correlated with Spd and Spm concentrations and the ratios of Spd/Put and Spm/Put. Spraying of Spd or Spm to panicle at early grain-filling stage significantly enhanced activities of sucrose synthetase, adenine diphosphoglucose pyrophosphorylase, and soluble starch synthetase in inferior spikelets, resulting in improvement of grain-filling rate, seed-setting rate, and grain weight. Application of Put or methylglyoxal-bis (guanylhydrazone) (MGBG, an inhibitor of S-adenosyl- L-methioninedecarboxylase) exhibited an opposite effect. These results indicated a regulative function of polyamines during grain filling. The low grain-filling rate and grain weight in inferior spikelets of super rice are probably in relation to the low concentrations of Spd and Spm and the small ratios of Spd/Put and Spm/Put in inferior spikelets.

Variation of grain Cd and Zn concentrations of 110 hybrid rice cultivars grown in a low-Cd paddy soil

Enhanced Cd uptake and Zn depletion in rice grains and high potential for food Cd exposure by the high-yielding hybrid cultivars of China had been addressed. A field experiment was conducted in 2006 to determine the difference in grain Cd and Zn between cultivars. Total 110 cultivars including super rice and common hybrid rice cultivars were grown on a single paddy soil (Entic Haplaquept) with a neutral reaction and low total Cd content. Grain Cd and Zn concentrations were determined with graphite atomic adsorption spectrophotometer (GFAAS) and flame atomic adsorption spectrophotometer (AAS) respectively. Wide variation of Cd content in grain was found in a range of 0.004-0.057 mg/kg, while the Zn content in a range of 10.25-30.06 mg/kg among the cultivars. Higher Cd but lower Zn concentration in grains of super rice cultivars was observed compared to the common hybrid ones. A highly significant positive linear correlation of grain Cd/Zn with grain Cd was found for super rice and common hybrid cultivars, meanwhile much higher slope for these hybrid cultivars than the reported non-hybrid cultivars was also observed. Using the limit value of the Chinese chemical guidelines for foods (MOHC and SSC, 2005), calculated potential risk of food Cd exposure with "Zn hungry" through diet intake was prominent with all the studied 110 hybrid rice cultivars, possessing high potential health problems for rice production in South China using the super rice cultivars. Breeding of genotypes of rice cultivars with low grain Cd and low Cd/Zn ratio is needed for rice production in acidic red soils where Cd bioavailability is prevalently high.