| The pursuit of high yield is the eternal theme of rice research and development. Presently, rice planting area had basically reached the top limit because of the serious shortage of resources of land and water. Therefore, to improve the grain yield per unit area was one of the main approaches of increasing rice productivity. To achieve this goal, all sorts of tentative ideas and approaches were proposed by government and researchers, such as "High Yield Founding","Food High-yielding Project","Super Rice", etc. Under the concerted collaboration of administrative, research and promotion units, a multitude of major breakthroughs occurred in super rice in China. To2013, China’s super rice varieties had reached as many as101. Among them, indica super rice was mainly hybrid rice, while all of japonica super rice were conventional rice. Therefore, to study population productivity between super hybrid indica combinations and conventional japonica super rice and their forming ecological and physiological characteristics under the high-yielding cultivation conditions, was of important theoretical significance and production practices. With indica or japonica rice planting simultaneously under the condition of rice-wheat double cropping rotation, partial late-maturing high-yielding indica and japonica super rice varieties (medium-maturing medium indica rice and early-maturing late japonica rice) on the premise of full heading and maturity being accomplished and making full use of temperature and solar radiation were chosen as materials in Suzhong region in2011-2012, and then supporting high-yielding cultivation and management measures, to bring their yield potential into play. On this basis, difference of yield formation mechanisms and ecological and physiological characteristics between the two typed-varieties was analyzed, and growth advantages and high-yielding mechanisms of japonica rice were illustrated, to provide evidences for the rational use of super rice and its excavation of high yield potential. The main results were as follows:1. Grain yield, panicle numbers, total spikelets, setting percentage, storage capacity, total filling, ratio of productive tillers, grain density, ratio of No. of branches of primary branches to No. of branches of secondary branches, ratio of total grains of primary branches to total grains of secondary branches, No. of branches of primary branches per panicle, grains per branch of primary branches, total grains of primary branches per panicle, seed-setting rate of primary branches, seed-setting rate of secondary branches, the final weight of a kernel, the time reaching the maximum grain-filling rate, the weight of a kernel at the time of maximum grain-filling rate, active grain-filling period and effective grain-filling period of japonica rice were higher than indica rice, while spikelets per panicle,1000-grain weight, panicle length, grain weight per panicle, No. of branches of secondary branches per panicle, grains per branch of secondary branches, total grains of secondary branches per panicle, initial grain-filling potential, maximum grain-filling rate and mean grain-filling rate followed an opposite tendency accordingly. However, no significant trend was observed for the ratio of the weight of a kernel at the time of maximum grain-filling rate to the final weight of a kernel between indica and japonica rice. Although the grain-filling processes of indica and japonica super rice were all asynchronous types, the phenomenon of two-stage grain-filling was more illustrious in indica rice. The grain-filling of indica rice started quickly and accumulated rapidly with short duration, declined fast in the end. The grain filling at the early, middle and late stage for inferior grains of japonica rice were higher than indica rice with the increasing range of0.73%,2.59%,3.43%, respectively, which suggested that the advantages of japonica rice would go larger and larger with the advancement of grain-filling. The stable-increasing-stable-decreasing tendency of population stems and tillers, multi-panicles, rational panicle structure, high seed-setting rate, stable and long duration grain-filling and high quality grain-filling for the inferior grains at the later period of grain-filling were the key points of enlarging sink, promoting the enrichment, stable yield and high yield of japonica rice.2. Dry matter accumulation, LAD, CGR and NAR at the early growth stage (from transplanting to jointing), leaf length, leaf base angle, angle between stem and leaf and drooping angle in top three leaves, leaf area decreasing per day after heading and harvest index of japonica rice were less than those of indica rice significantly, while dry matter accumulation, LAD, CGR and NAR at the middle and later growth stages (from jointing to maturity), ratio of leaf area of productive tillers, ratio of leaf area of top three leaves, grain-leaf ratio (spikelets per cm2leaf area, filled grains per cm2leaf area and grain weight per cm2leaf area), maximum leaf area index, total filling, grain yield, biological yield, maximum output and apparent output and their ratio were larger than those of indica rice significantly. Although dry matter weight per stem of japonica rice at the main growth stages was lower than that of indica rice, the superiority of population quantity suggested that japonica rice would possess higher dry matter accumulation and leaf area. With the advancement of growth and development, the superiority of photosynthesis and matter production of japonica rice was increasing, with a higher dry matter accumulation more than that of indica rice25d after heading approximately. The growth potential of japonica rice remained strong at the late period of grain-filling (from milky stage to maturity), while stored matter kept in the stem and sheath exported appropriately at the early period of grain-filling (from heading to milky stage), ensuring the security of efficient photosynthetic layer and the enrichment of high accumulation yield sink. Therefore, balanced formation of high biological yield, stable-increasing-slow-decreasing tendency of leaf area, and the large amounts of high efficient photosynthate production from jointing to maturity are the important characteristics and causes for the efficient and sustainable output of photosynthetic systems, more grain-filling and high yield formation in japonica rice.3. The growth processes of japonica rice in the field growth period were later than indica rice, with16.2days delayed for rice maturity and harvest time. No. of days of grain filling of japonica rice was longer than indica rice with the increasing range of25.82%, significantly. Japonica rice had strong adaptability to low temperature, which was beneficial for prolonging heading and grain filling appropriately, lengthening No. of days of grain filling and growth duration, and increasing the utilization of temperature and solar radiation in late autumn. Grain yield, biological yield, grain yield per day, and No. of days, effective accumulated temperature, photosynthetically active radiation and solar energy utilization of the whole growth duration, and No. of days, effective accumulated temperature and photosynthetically active radiation of the major growth duration, and production efficiency of temperature from heading to maturity, and dry matter accumulation and solar energy utilization from jointing to maturity of japonica rice were higher than indica rice significantly, while grain filling rate and production efficiency of temperature of the critical period from sowing to heading and the whole growth duration, and dry matter accumulation and solar energy utilization from sowing to jointing followed an opposite tendency accordingly. Correlation analysis showed that, grain yield of rice was found to be positively associated with No. of days of growth duration, grain yield per day and No. of days of grain filling significantly, while negatively related to grain filling rate significantly. Moreover, biological yield was highly significantly correlated with effective accumulated temperature, photosynthetically active radiation and solar energy utilization of the whole growth duration significantly, while there was a negative correlation between biological yield and production efficiency of temperature of the whole growth duration, though not significantly. Therefore, based on stabilizing and raising the utilization of temperature and solar radiation, grain yield per day and grain filling rate, the increment of effective accumulated temperature and photosynthetically active radiation improved by lengthening growth duration, especially for grain filling, could increase periodic dry matter accumulation and biological yield, which was one of important approaches and characteristics of high productivity of japonica rice.4. There were significant differences in the main quality characteristics between indica and japonica super rice among years, types, cultivars and the interaction effects of two-factors and three-factors. Brown rice rate, milled rice rate, head rice rate, gel consistency, peak viscosity, trough viscosity, final viscosity and peak time of japonica rice were higher (or longer) than indica rice, while chalky grain rate, chalkiness size, chalkiness degree, length-width ratio, amylose content, protein content, breakdown and pasting temperature followed an opposite tendency accordingly. However, no significant trend was observed for setback between indica and japonica super rice. Correlation analysis indicated that, daily mean temperature, daily highest temperature and daily lowest temperature had positive effects on appearance and nutritional quality, while negative effects on milking quality and cooking and eating quality. However, daily mean temperature difference and daily mean sunshine duration were not significantly correlated with rice quality characteristics. Therefore, it was one of important quality characteristics of japonica rice to form higher white rice yield and viscosity as well as lower chalkiness and protein stably and cooking delicious rice.5. Characteristics of nitrogen uptake, utilization and translocation between indica and japonica super rice were as follows.(1) The averages of grain yield, total N accumulation and N uptake per100kg of grain of japonica rice were10.89t/hm2,224.50kg/hm2,2.79kg, significantly higher than indica rice, with the increasing range of13.21%,32.74%,17.45%, respectively. Japonica rice was provided with large N accumulation as well as significant advantages of efficient and effective N absorption.(2) N content of leaf, stem, sheath, panicle at heading and maturity as well as the entire rice plants for the whole growth duration of japonica rice were higher than indica rice significantly.(3) N recovery efficiency and N agronomic efficiency of japonica rice were higher than indica rice, though not significantly, while N physiological efficiency, N using efficiency for grain production, N using efficiency for biomass production and partial factor productivity of applied N followed an opposite tendency accordingly, with all the indicators reaching a significant level with the exception of N physiological efficiency.(4) At maturity stage, ratios of N accumulation in stem-sheath and leaf of japonica rice were higher than indica rice significantly, but with an opposite trend for the ratio of N accumulation in panicle, which promised that N harvest index of indica rice would be higher than japonica rice significantly.(5) N translocation amount, apparent N translocation rate and N translocation conversion rate in stem-sheath and leaf from heading to maturity of japonica rice were lower than indica rice, with all the indicators reaching a significant level except for N translocation conversion rate of sheath.(6) High N grain of indica rice was almost contributed by export and translocation of store N kept in the source organs at heading, and N high-speed absorption at the middle and later growth period (from jointing to maturity) were the major factors of high total N accumulation for japonica rice. Therefore, on the basis of stabilized N uptake at the early growth stages (transplanting-jointing stage), increasing periodic N uptake rate and periodic N accumulation significantly, especially for the middle and later growth stages (jointing-maturity stage), was the key point of harvesting high total N accumulation and grain yield of japonica rice stably.6. Root morphological and physiological characteristics between indica and japonica super rice were as follows.(1) For the whole growth duration, root-shoot ratio, single root length, root germinating number, root germinating volume, root germinating dry weight, root bleeding per spikelet, number of panicles, total spikelets, seed-setting rate and grain yield of japonica rice were higher than those of indica rice, while root diameter, spikelets per panicle and1000-grain weight followed an opposite tendency, with root-shoot ratio, single root length, root bleeding per spikelet, number of panicles, spikelets per panicle, seed-setting rate and grain yield being a significantly different.(2) Before heading, dry weight of root, total root length, root number, root volume and total absorbing surface area of root per stem and root density of japonica rice were lower than those of indica rice, though not significantly, and higher than those of indica rice significantly at maturity.(3) Before jointing, active absorbing surface area per stem and ratio of active absorbing surface area to total absorbing surface area in japonica rice were less than those in indica rice significantly, which showed an opposite trend after jointing.(4) Population indicators of morphological and physiological characteristics of japonica rice except for population root dry weight at jointing and root number of population at jointing and heading were higher than those of indica rice significantly.(5) Root bleeding intensity during0-35d after heading was higher in japonica rice than in indica rice significantly whether it was based on a single stem or population.(6) Ratio of root dry weight in the0-10cm layer to total root dry weight was lower in japonica rice than in indica rice significantly, with an opposite trend for the>10cm layer, which indicated the deep-rooted characteristic of japonica rice can strengthen its resistance to lodging and premature senescence. Compared with super hybrid indica rice, root growth advantages of conventional japonica super rice after heading were increased, especially for population growth advantages, and all the root morphological and physiological characteristics indicators of japonica rice at maturity were better than those of indica rice, which is the important cause and assurance for high-yielding formation of japonica rice.7. Characteristics of lodging and supporting of culm between indica and japonica super rice were as follows.(1) Grain yield of japonica rice was higher than indica rice significantly, with the increasing range of11.79%. For the culm of0-20cm from the bottom, bending moment of japonica rice was higher than indica rice significantly and lodging index developed an opposite trend as it, no lodging phenomenon, compared to apparent lodging rate in the field of12.35%,13.05%for Yangliangyou6and Liangyoupeijiu, respectively.(2) For all the four basal internodes, breaking resistance and lodging index of japonica rice were less than indica rice significantly, while bending moment followed an opposite tendency.(3) Length of each internode and plant height, outer diameter of basal internode, stalk type index, height of gravity center and ratio of gravity center height to plant height of japonica rice were lower than indica rice significantly, with an opposite trend for ratio of neck internode length to stalk length.(4) Culm diameter and wall thickness for all the six elongated internodes of japonica rice were less than indica rice, with culm diameter from1st internode from the bottom to4th internode from the bottom reaching a significant level.(5) Dry weight of culm of each internode in japonica rice was lower than indica rice and dry weight of leaf sheath of each internode in Liangyoupeijiu was higher than the other three varieties significantly. Dry weight of unit internode for the second internode from the bottom of japonica rice was slightly higher than indica rice, while the opposite trend was presented for the others.(6) Retaining force per hill and buckling resistance of japonica rice were greater than indica rice significantly, while recovery after pushing followed an opposite tendency accordingly. Therefore, japonica rice was provided with strong ability of retaining and lodging, and strong recovering ability was improved by indica rice. Moreover, for japonica rice, high yield and lodging can be achieved at the same time, which may be related to its optimized characteristics, such as little breaking resistance, large bending moment, low plant height, appropriate matched-internode, low height of gravity center, enough enriched-matter of basal internode, and so on.These results can provide references for the new round of "indica rice to japonica rice" in Jiangsu region and similar ecological rice areas and even the whole southern suitable areas for japonica rice. However, local natural and social resources should be taken into account in the course of large-scale extension and production, persisting in "just indica rice if suitable for indica rice and just japonica rice if suitable for japonica rice". Moreover, several questions such as weak heat-resistance of species, large agricultural inputs, heavy environmental pollution, poor resistance to diseases and pests, insufficient storage techniques, mismatched production habits, stick-in-the-mud production facilities in some areas, and so on, were in the way of "indica rice to japonica rice", yet to further study and research. |
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