Zhong-Yang Huo

Difference of Root Morphological and Several Physiological Characteristics between Indica and Japonica Super Rice Varieties

The objective of this study was to reveal the difference of dry matter accumulation and its distribution, and the main morphological and physiological characteristics in roots between indica and japonica super rice, and their relationship with yield formation. A field experiment was conducted using two main representative super hybrid indica combinations and two conventional japonica super rice varieties in wheat-rice double cropping regions. Dry weight of root, total root length, root number, root volume, root absorbing area, root germination ability and root bleeding intensity after heading for both single stem and population, root-shoot ratio, single root length, root diameter, root density, root bleeding per spikelet, root distribution in the soil at heading and yield components were analyzed systematically. Results showed 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 and 1000-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 during 0–35 d 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 the 0–10 cm layer to total root dry weight was lower in japonica rice than in indica rice significantly, with an opposite trend for the 10 cm 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.

Photosynthetic Characteristics of Flag Leaf in Rice Genotypes with Different Nitrogen Use Efficiency

Abstract To identify the photosynthetic mechanism of nitrogen (N) absorption and utilization in different rice (Oryza sativa L.) genotypes, relationships between photosynthetic characteristics of flag leaf and N use efficiency were investigated in 6 N-efficient and 6 N-inefficient rice genotypes with variable N use efficiency. The abilities of seed setting of the genotypes were also analyzed. The N application rate was 225 kg ha−1 for all genotypes. During grain filling, chlorophyll content, N content, net photosynthetic rate, photosynthetic function duration, maximum photochemical efficiency (Fv/Fm), potential photochemical efficiency of photosystem II (Fv/Fo), actual photochemical efficiency of photosystem II (ΦPSII), photochemical quenching coefficient (qP), and nonphotochemical quenching coefficient (qN) of flag leaf were obviously higher in the N-efficient genotypes than those in the N-inefficient genotypes. All these indexes were positively correlated with N use efficiency and seed-setting ability. Compared with the N-inefficient genotypes, the N-efficient genotypes had more favorable characteristics of photosynthesis and longer photosynthetic function duration. Besides, their PSII was steady for the large potential of converting light energy into electrochemical energy, and nonphotochemical quenching could also protect the photosynthetic apparatus. The accumulation of photosynthate and the seed-setting ability were enhanced in the N-efficient genotypes compared to the N-inefficient genotypes. Simultaneously, the N absorption and utilization of N efficient genotypes were improved through feedback regulation of roots and shoots.

Comparison of Culm Characteristics with Different Nitrogen Use Efficiencies for Rice Cultivars: Comparison of Culm Characteristics with Different Nitrogen Use Efficiencies for Rice Cultivars

The morphological and physiological characteristics of low-yielding and low N-efficiency,high-yielding and medium N-efficiency,high-yielding and high N-efficiency of rice cultivars were investigated using six representative japonica varieties under their respective optimal N application levels.The results showed that compared with low-yielding varieties,high-yielding varieties showed shorter basal 1st internodes,longer basal 6th internodes,increased plant height,larger culm diameter and wall thickness,significantly higher dry weight of stem and sheath,obviously increased K and Si content in culm and sheath,and a higher ratio of Si to N.As a result of their improved stalk physical characteristics and the different chemical compositions,the comprehensive breaking resistance of the culm of high-yielding cultivars was improved evidently,and the lodging index reduced as well.The cultivars with different N-efficiencies displayed diverse culm morphological and physiological characteristics even though they were all in one high-yielding level.Comparing with medium N-efficiency genotypes,the high N-efficiency ones had longer 4th and 5th internode lengths,increased culm wall thickness,in spite of slightly decreased culm diameter,resulted in higher dry weight and strengthened plumpness status of culm,significantly decreased content of Si in stem and sheath,decreased N content,and remarkably unchanged K content.Given these results,for the purpose of further increasing the nitrogen fertilizer use efficiency of the high-yielding varieties,it would be favorable to properly increase 4th and 5th internode length,thus improving top three leaves configuration,to appropriately reduce the culm diameter while increasing wall thickness and filling degree for the sake of stalk breaking resistance and transporting capability,and to properly reduce the content of Si in culm and sheath tofacilitate the translocation of nitrogen.

Characteristics of Dry Matter Accumulation and Translocation in Rice Cultivars with High Yield and High Nitrogen Use Efficiency

The difference of dry matter production and translocation characteristics in low-yielding and low N-efficiency, high-yielding and medium N-efficiency, high-yielding and high N-efficiency rice cultivars was investigated using six representative japonica varieties under their optimum N supply levels, respectively. The results indicated that: with the increase of rice productivity, the total dry matter production amount significantly increased by 20.29% on average, and the dry matter accumulation amount and population growth rate increased on average by 15.05%, 27.04%, 24.75% and 15.05%, 28.38%, 23.00%, during the period before N-n (critical stage of productive tillering), from jointing to heading, and from heading to maturing, respectively, and decreased during the period from N-n to the jointing. Among the high-yielding varieties, with the nitrogen use efficiency increased, the tiller number per unit area at each growth stage showed a downward trend, and significantly reduced on average by 5.76%, 11.61%, 7.01%, and 5.70% at N-n, jointing, heading and maturing, respectively, but ratio of productive tillers to total tillers significantly increased. At each growth stage, the dry matter accumulation amount showed a declined tendency, and reduced on average by 12.18%, 10.54%, 8.29%, and 5.01% at N-n, jointing, heading and maturity, respectively, but harvest indexsignificantly increased. During the period from heading to maturing, dry matter accumulation rate increased on average by 5.40%, the population growth rate increased on average by 5.19%. The results above showed that proper control for population growth before heading, maintaining a high growth rate after heading and a higher harvest index were the important dry matter accumulation characteristics of the cultivars with high-yielding and high nitrogen use efficiency.

Characteristics of Super-high Yield Population in Yongyou Series of Hybrid Rice

A field experiment was conducted using the representative indica-japonica hybrid rice Yongyou 11, Yongyou 12,Yongyou 13, Yongyou 15, and Yongyou 17 to compare between super-high and high yield populations formed by the regulation of cultivation measures. The results showed that the spikelets of the super-high yield population was higher than that of high yield population, with difference very significant, but the seed-setting rate and 1000-grain weight of the super-high yield population were lower than those of high yield population. The average spikelets per panicle was significantly higher than that of high yield population, meanwhile the number of the primary and secondary branches and total grains were higher than those of high yield population, showing a significant or very significant difference. The dry matter accumulation of the super-high yield population was a little lower than that of the high yield population at the jointing stage, but higher at heading and maturity stages. From the critical leaf-age for productive tillers to jointing stage, the super-high yield population had a steady growth with less ineffective tillers and lower peak number of tillers after jointing stage, the super-high yield population had a steady decline in number of tillers and had higher productive tillers rate, leaf area index, photosynthetic potential and dry matter accumulation, compared with the high yield population. The super-high yield population had higher culm diameter and culm wall thickness in the basal first, second and third internodes, as well as higher bender moment and anti-broken strength, and lower lodging index than the high yield population.

Effect of Ordered Transplanting and Optimized Broadcasting on Super High Yield and Photosynthetic Productivity and Exploration of Rice Super High Yield Model

Rice seedling broadcasting is a technique of light and simple cultivation method in China and the stable super high yield from using the method relies on the ordered plantation of rice.Three planting methods including ordered transplanting(OT),optimized broadcasting(OB) and cast transplanting(CT) using dry-raising seedlings in plastic plates were compared with mechanical transplanting(MT) to investigate the photosynthetic productivity and matter accumulation characteristics during the formation of super high yield in respect of seedling establishment,tillering,LAI,grain-leaf ratio,photosynthetic potential,matter production,accumulation and translocation in late stages.Using methods of ordered transplanting and optimized broadcasting rice seedlings had the better population quality with earlier seedling establishment at the beginning,and their LAI,leaf area duration,grain-leaf ratio,matter production,accumulation in each growing stage,and net photosynthetic rate and matter translocation in later growing stages were all significantly or very significantly superior to those of cast transplanting.Moreover,in late growing stages,they showed comparatively better population light transmittance and ventilation,slower senescence,and higher matter production and lodging resistance as well.The transplanting hill number for of 3-and 2-hole closely gathered plates were 30–60 percent less than that for single-hole ones,which improved transplanting speed.Although 3-hole seedlings had earlier seedling establishment in early growing stage,2-hole seedlings kept higher matter production and lodging resistance in middle and late growing stages.Eventually,two hole seedings had higher yield than 3-hole seedlings and 1-hole seedlings.With their higher population starting point,earlier seedling establishment,proper matter accumulation in early growing stage as well as higher matter production,accumulation and translocation ability in later growing stages,ordered transplanting and optimized broadcasting methods were capable of leading to the stable super high yielding cultivation of super rice.Two-hole plate transplanting seedlings showed better matter production and obvious growth superiority during the whole growth stage,and 3-hole one also showed growth superiority in some aspects,which could lead us to the conclusion that 2-and 3-hole plate seedlings ordered transplanting are new-typed cultivation patterns of super high yielding in super rice.