Study On Yield Formation Of Double-Cropping High-Quality Late Indica Rice

With the rapid development of China’s economy and the continuous improvement of people’s living standards,the demand for high-quality rice is increasing.At present,great progress has been made in the breeding and promotion of high-quality rice varieties in China.In the double cropping rice area in the middle and lower reaches of the Yangtze River,the planting area of high-quality rice accounts for 63.6%of the total planting area of rice,of which about 97.6%of the high-quality rice varieties are indica rice.Due to the suitable climatic conditions for the late rice season in the double-cropping rice area are very conducive to the formation of high-quality rice yield and quality,high-quality late indica rice occupies an absolute position in the production of high-quality rice.However,due to the relatively lagging research on the growth characteristics and supporting cultivation techniques of high-quality late indica rice,the stability and high yield of high-quality rice are poor,and the quality is easy to decline.Therefore,in this study,20high-quality late indica rice varieties widely planted in the double-cropping rice areas in the middle and lower reaches of the Yangtze River were selected as the test materials.From the three dimensions of taste quality grade（special high-quality,ordinary high-quality）,yield level（low-yield,medium-yield,high-yield）,and variety type（conventional rice,hybrid rice）,the characteristics of plant panicle type,yield formation and dry matter accumulation of different types of high-quality late indica rice varieties were clarified.On this basis,two high-quality and high-yield synergistic varieties and two ordinary high-yield varieties were selected as materials,and different nitrogen fertilizer treatment levels were set up to clarify the yield formation law and physiological characteristics of high-quality late indica rice,aiming to provide a theoretical basis for the synergistic improvement of high-quality,high-yield and high-efficiency of high-quality late indica rice in double-cropping rice areas.The main conclusions are as follows:1.Compared with ordinary high-quality varieties,high-yield varieties and hybrid rice varieties,the plant types of special high-quality varieties,low-yield（or medium-yield）varieties and conventional rice varieties showed high plant height,fine stem,long and narrow leaves in the second leaf from the top,and no difference in leaf base angle and leaf area index in the third leaf from the top.The spike type showed that the number of primary branches and secondary branches was less,the grain density was low,and the spike length was not different.The dry matter accumulation and translocation showed that the dry matter translocation before anthesis and its contribution rate to grain were high,the dry matter quality after anthesis,dry matter quality at maturity stage and harvest index were low,and there was no difference in dry matter quality at heading stage.The source-sink relationship showed that spikelet number/leaf area,filled grain number/leaf area,grain weight/leaf area ratio were low.The yield and composition showed that the number of effective panicles was more,the number of grains per panicle and the number of spikelets per unit area were less,the yield level was low,and the panicle rate,filling percentage and1000-grain weight were not different.It can be seen that the high-quality varieties,low-yield（or medium-yield）varieties,and conventional rice varieties mainly restrict the yield increase due to insufficient spikelets per m^-2,low grain-leaf ratio,and low dry matter accumulation after flowering.2.The panicles per m²of high-quality and high-yield varieties was more,while the number of spikelets per panicle was less,resulting in a significant decrease of7.88%-11.32%in the number of spikelets per m²,a significant decrease of2.88%-4.54%percentage points in seed setting rate(N₂₂₅),and a significant decrease of10.08%-12.69%in 1000-grain weight（only Yexiangyoulisi）.The dry matter weight at heading stage and its contribution rate to grain were significantly increased by8.77%-16.77%and 18.76%-34.67%,respectively,while the dry matter accumulation after flowering,dry matter production at maturity and harvest index were significantly decreased by 25.44%-51.89%,2.12%-11.25%and 4.68%-15.17%,respectively.The initial filling rate,maximum filling rate and average filling rate of upper,middle,lower and all grains were significantly lower than those of common high-yield varieties,while the time to reach the maximum filling rate and active filling time were significantly lower than those of the latter.It can be seen that the number of spikelets per unit area,relative growth rate after flowering,dry matter quality after flowering and filling rate of high-quality and high-yield varieties were lower than those of ordinary high-yield varieties,resulting in a significant decrease of 7.70%-19.24%in yield.3.The leaf area index of high-quality and high-yield varieties was significantly higher than that of ordinary high-yield varieties,while the SPAD value of flag leaf,net photosynthetic rate and grain leaf ratio（spikelet number/leaf area,filled grain number/leaf area,grain weight/leaf area）at young panicle differentiation stage,heading stage and15 days after heading were significantly lower than those of the latter.Solar radiation interception and interception rate were significantly higher than those of common high-yield varieties,while solar radiation utilization efficiency（RUE）was significantly lower than that of the latter.The anti-aging characteristics of flag leaves during grain filling stage were significantly better than those of common high-yield varieties.4.The root biomass,root length,root surface area and root volume of high-quality and high-yield varieties at 0-10 cm and 0-25 cm soil depth were significantly lower than those of ordinary high-yield varieties,while the root biomass,root length,root surface area and root volume at 10-25 cm soil depth were significantly higher than those of the latter.The root activity at heading stage was lower than that of common high-yield varieties,while the root activity at late filling stage was higher than that of the latter.The absorption and utilization efficiency of nitrogen,phosphorus and potassium in pre-anthesis plants were significantly higher than those in common high-yield varieties,while the accumulation and utilization efficiency of nitrogen,phosphorus and potassium in post-anthesis and whole growth period were significantly lower than those in the latter.The yield of high-quality and high-yield varieties under high nitrogen treatment(N₂₂₅)was 2.24%-3.71%lower than that under medium nitrogen treatment(N₁₆₅),while the yield of ordinary high-yield varieties increased by 6.60%-10.15%.The main reason was that the sink-source relationship of high-quality and high-yield varieties deteriorated under high nitrogen treatment,and the transport of carbohydrates and nitrogen in stems and leaves was hindered,resulting in a significant decrease in seed setting rate and nitrogen use efficiency.It can be seen that increasing nitrogen fertilizer input is not conducive to the improvement of yield of high-quality and high-yield late indica rice varieties.Due to the high yield and high quality of late indica rice varieties under high nitrogen treatment(N₂₂₅)still showed a significant increasing trend,while the middle and low yield and high quality of late indica rice showed a decrease or no significant difference.Therefore,it is necessary to adopt different nitrogen fertilizer application strategies for high-yield and medium-low-yield high-quality late indica rice.High-yield high-quality late indica rice can be applied with appropriate panicle fertilizer on the basis of conventional nitrogen fertilizer application,while medium-low-yield high-quality late indica rice is not necessary.In addition,in view of the slow senescence of high-quality late indica rice in the late filling stage,the water management strategy of high-quality late indica rice should be:it is not appropriate to cut off water too early in the late growth stage.