Effects of Postponing N Application on Metabolism,Absorption and Utilization of Nitrogen of Summer Maize in SuperHigh Yield Region

[Objective] The aim was to explore effects of application postponing of N fertilizer and the mechanism of yield increase in order to provide references for N fertilizer application in a rational way. [Method] In a super-high yielded region of summer maize, field experiment was conducted to research effects of N fertilizer postponing on key enzymes of N metabolism, yield of maize and N fertilizer use. [Result] After application of N fertilizer was postponed, NR, SPS and GS activities of ear-leaf of summer maize increased by 11.99%-34.87%, 8.25%-10.64% and 10.00%- 16.81% on the 28^th d of silking; content of soluble sugar in leaves enhanced signifi- cantly and accumulated nitrogen increased by 5.00%-9.74% in mature stage. The postponing fertilization of ＂30% of fertilizer in seedling stage＋30% of fertilizer in flare- opening stage＋40% of fertilizer in silking stage meets N demands of summer maize in late growth period. Compared with conventional fertilization, the maize yield, agro- nomic efficiency and use of N fertilizer all improved by 5.05%, 1.75 kg/kg and 6.87%, respectively, after application postponed. [Conclusion] Application postponing of N fertilizer maintains activity of NR, GS and SPS higher and coordinates metabolism of C and N in late growth period, to further improve yield of maize.

Photosynthetic Characteristics of a Super High Yield Cultivar of Winter Wheat During Late Growth Period

The mechanism of high yield of winter wheat in the field at late growth period was investigated by measuring the photosynthetic characteristics of photosystem Ⅱ （PSⅡ） and xanthophylls cycle, which could provide physiological reference for breeding. Weimai 8 （W8）, a super high yield cultivar, and Lumai 14 （L14）, a control cultivar were object. The photosynthetic rate （Pn）, parameters of chlorophyll fluorescence and chlorophyll content were measured. The Pn, maximum photochemical efficiency of PSII （Fv/Fm）, quantum yield of PSII electron transport （ΦPSⅡ）, efficiency of excitation energy capture by open PSII reaction centers （Fv＇/Fm＇）, and photochemical quenching coefficient （qP） were higher in Weimai 8 compared to that in Lumai 14, a commercial high yield cultivar. Furthermore, Weirnai 8 showed a lower non- photochemical quenching coefficient and a lower de-epoxidized ratio of the xanthophyll cycle pigments than of Lumai 14 at late growth period. At mature stage, chlorophyll content of different leaves decreased both in Weimai 8 and Lumai 14. Chlorophyll content in flag, second and third leaf from the top of plant decreased more in Lumai 14 than in Weimai 8. These results suggested that Weimai 8 had more antenna pigments to absorb light energy, and had higher photosynthetic capability and photochemical efficiency of PSⅡ. The yield of Weimai 8 was also higher than that of Lumai 14.

Hybrid rice achievements, development and prospect in China

This article reviews the history and progress of hybrid rice development. Hybrid rice research was initiated back in 1964, and commercialized in 1976. Three-line and two-line system hybrid rice were developed in 1974 and 1995, respectively. Research on super hybrid rice, which was first launched by Ministry of Agriculture, China in 1996, is discussed, and the great progress of super hybrid rice had been achieved with a new yield record by 15.4 t ha^-1 in the 6.84 ha demonstration location in Xupu, Hunan Province, China in 2014. And the mechanism of heterosis, the techniques of hybrid seed production and the modern field managements in hybrid rice over the past decades are also discussed. Additionally, this article dealt with the intellectual property protection（IPR） and development of hybrid rice seed industry in China. Major factors that constrain hybrid rice development are analyzed and possible solutions to this problems are proposed. Finally, the authors present methods to further increase production yield, and propose an improvement for breeding super high-yielding hybrid rice based on these methods.

Experimental and genomic evidence for the indica-type cytoplasmic effect in Oryza sativa L.ssp.japonica

Cytoplasmic effects are important agronomical phenomena that have generated widespread interest in both theory and application. In the present study, five high yield rice cultivars（Oryza sativa L. ssp. japonica） in large-scale cultivation in northeast China were determined to possess Oryza sativa L. ssp. indica-type cytoplasm using cytoplasmic subspecies-specific molecular markers. This was confirmed by cytoplasmic genome-wide single nucleotide polymorphisms（SNPs） and functional gene sequencing. Two of these five japonica cultivars were core breeding parents with high yield and the other three were super-high-yield varieties registered by the Ministry of Agriculture of China. We constructed nuclear substitution lines to further demonstrate whether and how this indica-type cytoplasm contributed to yield improvement by comparing yield components. The results showed that under the same japonica nuclear background, the lines with indica-type cytoplasm had a significant decrease in tillers in exchange for increased grain number per panicle compared with their recurrent parents. Our results implied that botanical basis of this cytoplasmic effect was to reduce the plant＇s branching differentiation to produce more floral organs under the constant nutrition. Our findings open another door for the utilization of inter-subspecific hybridization for the improvement of rice cultivar.