| China’s Yangtze River drainage area is the main producing areas of rapeseed, where94 rapeseed breeding varieties(or lines) were used as the experimental materials to compare the difference of harvest index(HI) and variation range among varieties, by setting the varieties comparison test, sowing date, density and nitrogen fertilizer trials. To make clear the correlation between the harvest index and phasic development,accumulation and distribution of dry matter, yield; to determine the effect of sowing date,density and nitrogen rate and temperature difference among years on the rapeseed harvest index and its range of variation; to explore the physiological mechanism of formation of rape harvest index that influenced by nitrogen use efficiency and15 N accumulation and translocation. Summarize the variation of harvest index and its formation law, and provide the theoretical basis for rapeseed variety breeding and high-yield cultivation.Harvest index of different cultivars on rapeseed varies. Each growing stage was quite different in different rapeseed varieties(lines), the days of whole growth stage were195-214 d in the early sowing trial and 182-192 d in the late sowing trial. The period of duration didn’t have obvious relevance with HI.Under the condition of different years and different sowing date, harvest index among varieties were very different that can ranged between 0.193-0.449. High harvest index variety of low biomass yield varieties type is difficult to achieve high yield, the high harvest index variety can achieve a high yield only when reached a medium biomass yield.Harvest index and the dry weight of stems organ in mature was significantly negative correlated; With the pod dry matter accumulation and its proportion were significant positive correlated; With seed-pericarp ratio and seed number per pod were both significantly positively related. Therefore, during the development process, by reducing the percentage of dry matter distribution of stem; by Increasing the percentage of dry matter distribution of pod; by Increasing the photosynthate transport capacity from peel of pod to seed; by Improving the ability of forming seed to increase the "library", allof these are conducive to improving rapeseed harvest index. The harvest index and nitrogen harvest index, seed nitrogen production efficiency, all showed a significant positive correlation(r = 0.948**, r = 0.989**, n = 6), nitrogen utilization of high harvest index varieties was also high, and it could transfer more nitrogen to the seed at maturity,15 N tracer tests further confirmed this conclusion. With higher HI, more nitrogen transferd to the seed at maturity stage. In the high HI cultivar, Huaza 10 and Huazao 291, 59.1%15N transferd to the seeds, while only 46.9% in low HI cultivar such as Dadi 95 and Zhongyou 7819.Biological yield and economic yield both reduced, while harvest index increased by delayed sowing date. The different sowing date trails that during 2010--2013 three years with nine rapeseed varieties showed that, with the delay of sowing date, the days of duration stage were shortened from an average of 210.1 days to 191.5 days; The plant height, stem diameter and branch number were reduced from an average of 160.0 cm,13.7 and 6.1 to 148.8 mm, 12.5 mm and 5.3 respectively; The leaf number and maximum number of green leaves were reduced from 28.6 and 18.1 to 22.1 and 13.5 respectively;The maximum photosynthetic area index was reduced from 6.0 to 5.3; Finally the mature per plant dry matter accumulation reduced from an average of 56.0 g to 39.6 g.At the same time, the distribution ratio of stem dry matter reduced from 36.3% to47.6% and of pod dry matter raised from 57.9% to 44.6%; Seed-pericarp ratio raised from1.10 to 1.16; Seed number per pod increased from 15.5 to 17.4; Harvest index of three years increased from 0.298 to 0.342 on average with an increase of 14.6%. Nevertheless,three years average yields of early and late sowing trails were 2967.5 kg/hm2 and 2405.1kg/hm2 respectively with a decrease of 19.0%.With the increase of planting density from 150,000 plants/hectare to 750,000plants/hectare, biological yield and economic yield reached the peak at 60,000plants/hectare, but HI dropped markedly. The days of rape seedling stage and the budding stage were extended, while the days of the flowering stage and podding stage were shortened, thus, the days of whole growing stage of all rapeseed varieties shortened from 203.7- 212.7 days to 212.7-210.7 days.Plant height, stem diameter, main inflorescence length and number of branches per plant were also followed a downward trend with the increase of planting density, the maximum decline respectively were 19.6 cm, 5.8 mm, 13.0 cm and 4.0, ultimately, the plant dry matter accumulation showed from 55.2 g down to 16.8 g. The community biomass was increased first and then decreased, and at 600,000 plants/ hectare density achieve the maximum biomass of 12.2 t/hm2.At the same time, the distribution ratio of stem dry matter rose from 32.0% to 34.1%with the increase of planting density, while the distribution ratio of leaf and pod was a downward trend; Seed-pericarp ratio was decreased from 1.18 to 1.12.As the density increased, rapeseed yield was increased and the maximum yield was average of 3381.1kg / hm2.when the density was 600,000 plants/ hectare.At a certain range, economic yield and harvest index increased at the same time by increasing nitrogen utilization. The early and late sowing trails during showed that with the increase of nitrogen rate, the days of rapeseed seedling stage were shortened, and the days of budding stage, flowering stage and podding stage were prolonged. The whole growth stage of rapeseed were prolonged by 1.6 and 3.9 days respectively.Plant height, stem diameter, main inflorescence length, branch number and leaf number were increased with the increase of nitrogen rate, the difference of treatment N90 and N270 was significant, and the plant dry matter accumulation were increased by 19.1 g and 13.2 g respectively.Increasing nitrogen rate could improve leaf dry matter distribution ratio of flowering stage, Seed-pericarp ratio increased and seed number per pod decreased. From N0 to N270, HI increased. Above N360, cultivar Zhongyou 7819 and Zhongyou 36 declined,whlie Huayouza 62 and Huaza 9 kept growing. Amplitude of variation in different cultivars was 0.143-0.332. The effect and range of harvest index were significant different among different varieties with different nitrogen rate.Yields of two sowing date respectively increased from 1499.9 kg/hm2 and 1282.1kg/hm2 to 2821.6 kg/hm2 and 2409.1 kg/hm2 with increasing nitrogen application. |
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