Study On The Super High Yield Plant Type And The Photosynthetic Characteristic Of Yongyou 2640

Studies were conducted in the experimental farm of Yangzhou University in 2016 and 2017 using the indica-japonica hybrid rice Yongyou 2640 as the test material,and the conventional japonica rice Wuyunjing 24 and Nanjing 9108 as the CK.A split-plot design was adopted in this study with nitrogen application as the main plot and rice varieties as the split plot,with three repetitions.Three plant-types such as spike-cover type,middle type,and grass-cover type of rice varieties were formed through different nitrogen application rates under the same nitrogen amount 300 kg·hm-2.This study was conducted to study the high-yielding charatceristics and its photosynthetic physiology of Yongyou 2640,and to reveal the high-yield pathway and mechanism of Yongyou 2640.Our study would provide theoretical and practical basis for the super-high-yield breeding and cultivation of Yongyou 2640 and other indica-japonica hybrid rice.The main results were as follows:(1)The average yield of Yongyou 2640 was 11.25 t·hm-2 in year 2016 and 2017,which was 20.52%and 34.83%higher than Wuyunjing 24 and Nanjing 9108 respectively,reaching an extremely significant level.Yongyou 2640 had lower 1000-grain weight and panicle number per unit area,but the grain number per panicle was significantly more than that of conventional japonica rice,and the number of grains on the secondary branches of yongyou 2640 contributed as much as 60%to the total grain number,the total spikelets was significantly higher than that of conventional japonica rice,and the seed setting rate was 85.83%.The high yield of Yongyou 2640 was obtained by the more spikelets per panicle.Among the three plant types of Yongyou 2640,the middle type had the highest yield,the average yield of middle type were 11.88 t·hm-2 in year 2016 and 2017,which was 11.69%and 5.25%higher than that of spike cover type and grass cover type respectively.Compared with the conventional japonica rice,the middle type increased the yield of Yongyou 2640 more significantly.The number of panicle per unit area of middle type was lower than grass cover type,and the grain number per panicle was the highest,and the seed-setting rate and 1000-grain weight of middle type did not decrease significantly.The number of grains on the secondary branches of the middle type accounted for the highest proportion to the total grain number.(2)The plant height and stem thickness of Yongyou 2640 were higher than those of conventional japonica rice.The leaf average length and width of upper fifth leaves were the largest,and drooping angle of upper three leaves of Yongyou 2640 was smaller,and that of upper canopy leaves was larger,compared with the CK,the drooping angle from bottom first leaf to bottom fifth leaf increased gradually.At flowering stage,the LAI and high-efficiency leaf area ratio of the Yongyou 2640 were the highest,which ensureed the quantity and quality of the leaf source during the filling stage.Among the three plant types of Yongyou 2640,the optimal plant type structure is middle type in all three.the plant height of middle type was medium,which around 132 cm to 136 cm,middle type increased the stem thickness,which around 0.75 cm to 0.95 cm,and middle type increased the length and width of flag leaf of Yongyou 2640.The lower sag of the upper leaves of Yongyou 2640 canopy was maintained for middle type,which increased the overall photosynthetic utilization of the canopy.the high leaf area ratio were the highest of middle type at heading stage,and after heading,the LAI was medium of middle type(no significant difference from the grass cover type).(3)The canopy leaves photosynthetic capacity of Yongyou 2640 was the best.The nitrogen content,SPAD value,and photooxidation resistance of the leaves were higher than those of Wuyunjing 24 and Nanjing 9108,The SPAD value of the leaves had a slower attenuation and a long functional period.During 30 days after anthesis,the net photosynthetic rate,stomatal conductance,and transpiration rate of the upper canopy were the highest,the decline was the slowest,there was no significant difference between the value of Fv/Fm and Y(?)of Yongyou 2640 and conventional japonica rice,Fv/Fm value was in range of 0.8-0.85 and Y(?)value was in range of 0.7-0.8,and the decline was slowest.The activities of SPS,FBP and Rubisco in the flag leaves of each growth stage were higher than those of conventional japonica rice,and the PEPC activity was the lowest among the three varieties.Among the three plant types of Yongyou 2640,the photosynthetic capacity of middle type was the best.the total leaf nitrogen content and SPAD value of the middle type were medium,the nitrogen transported to the grain was the highest,and the SPAD value of the canopy leaves had a slowest attenuation,and the ability of photooxidation resistance of upper canopy leaves,especially the flag leaf,was the strongest;the photosynthetic parameters of upper canopy leaves of middle type are optimal,and the chlorophyll fluorescence parameter value were also in the optimal physiological range;the middle type increased the activity of Rubisco,FBP and PEPC in the flag leaf of Yongyou 2640,The SPS activity of the flag leaf was second only to that of grass cover type,the photosynthetic characteristic of middle type is optimal.(4)At maturity,Yongyou 2640 had the largest aboveground biomass,and the translocation capacity of dry matter in stems and leaves and NSC in stem-sheaths,but the dry matter contributed the lowest to the grain,and the NSC contributed the highest rate to the grain,Yongyou 2640 had sufficient source and fluent flow during filling period,Yongyou2640 had more advantages than conventional japonica rice.Among the three plant types of Yongyou2640,the above-ground biomass,the NSC transport,transport rate,and contribution rate in the stem and sheath of middle type were the highest,but the dry matter transport,the transport rate and the contribution rate to the grain in the stem and leaf were the lowest.