| Time of floral initiation largely determined the number of floral buds,and the amount of effective flower buds determined the number of pod and seed yield to a large extent.In the present study,three different maturing cultivars “1358”,“Zhongshuang No.11” and“Zheshuang No.8” were selected to conduct a series of comparison experiments,including sowing dates,fertilizer application and planting density.Floral initiation time were investigated systematically to reveal its relationship with climate change and agronomic managements.Furthermore,we studied the dynamic variation of flower bud number and its relationship with pod number and yield formation.We varied the nitrogen application rate and proportion allocated to pre-sowing,floral initiation and budding stages for earlyand medium-maturing varieties of rapeseed to estimate the optimal nitrogen application to obtain high seed yield of rapeseed through multiple regression.Meanwhile,rapeseed cultivars suffering terminal drought stress or not were carried out in glasshouse or field in Australia to figure out the temporal and spatial distribution of yield derived from flowers.Pooling all of the floral initiation date with historical climate,we constructed a multiplicative phenology model to distinguish and quantify the effects of photoperiod and temperature on pre-floral initiation phase for different maturing varieties.We also use this data to validate the APSIM＿Canola model to provide technical support for matching cultivar with suitable sowing dates to achieve optimum yield.The main results are as follows:1.Late-maturing varieties are more sensitive to low temperature,and early-maturing varieties are more sensitive to photoperiod.The results showed that the optimum temperature for the maximum developmental rate to switch into floral initiation quickly was about 23.9 °C,11.1 °C and 10.6 °C for “1358”,“Zhongshuang No.11” and“Zheshuang No.8”,respectively.The physiological developmental time(PDT)at prefloral initiation phase were 10.8d,23.9d and 25.1d for “1358”,“Zhongshuang No.11”and “Zheshuang No.8”,respectively.The critical day length of “1358” was longer than that of “Zhongshuang 11” and “Zheshuang 8”.The model showed that the relative vernalization effect driven by low temperature was significantly different among different maturing varieties.The medium-and late-maturing varieties “Zhongshuang No.11” and “Zheshuang No.8” had longer physiological vernalization time and needed lower temperature to fulfill vernalization requirement.2.The genes expression involved in floral initiation differed between early-and mediummaturing varieties.The floral initiation time of early-maturing variety “1358” have no difference between normal and low temperature treatments,and expression levels of most genes involved in flowering regulation network were not significantly differed.The low temperature significantly advanced the floral initiation time of mediummaturing variety “Zhongshuang No.11”,and this case could attribute to the regulation of FLC,SOC1 and LFY signaling pathways.Gibberellin signaling pathway may also be involved in the floral initiation under low temperature condition.3.Delaying sowing date increased the degeneration rate of floral bud,and increasing nitrogen fertilizer appropriately will reduce the degeneration rate.With the delay of sowing date,the ratio of fertile flower buds to total flower buds tended to decrease.The rate of flower bud degeneration could be reduced by 4%-9% by applying more nitrogen fertilizer.Averaged across growing seasons,sowing dates and genotypes,degeneration rate on raceme was 33% and,that on seven primary branches counted from apical to basal position of stem were 60%,58%,59%,68%,79%,93% and 99%,respectively.The bud degeneration was much more serious on branches than on raceme,especially the basal branches.4.Yield of rapeseed mainly derived from the flowers formed in 3.5 weeks after first flowering.The flowers that opened before 3.5 weeks after first flowering contributed to more than 98% of the seed yield,and the accumulated temperature at this stage was about 300 ℃d to 450 ℃d.Terminal drought occurred at the beginning of flowering shortened the effective flowering period to about 3 weeks.Increasing drought severity seriously reduced the final seed setting rate,resulting in a large reduction of yield.Drought occurred at pod stage has little effect on the number of pod,but it will hinder the grain filling process,resulting in the decrease of thousand seed weight and yield.5.Nitrogen application rate had no effect on the time of floral initiation,but nitrogen application at this stage have great benefit to yield.Coordinating application of nitrogen fertilizer is one of the important managements to coordinate the growth of vegetative stage and reproductive stage,and achieve high and stable yield.The results showed that the yield of “Huayouza No.9” could reach 3200 kg/ha under nitrogen application of 125kg/ha as base fertlilizer,75 kg/ha at floral initiation and 135 kg/ha at budding stage,respectively.For “Shengguang 127”,the nitrogen application should be about 120 kg/ha,45 kg/ha and 195 kg/ha at each stage to gain yield above 3200 kg/ha.6.The APSIM＿Canola model was calibrated based on our observed data to provide scientific guidance for rapeseed cultivation and management.The suitable sowing date of different maturity rapeseed varieties is mainly determined by the difference in vernalization requirement,and their response to photoperiod is negligible compared with that of temperature.The early-maturing variety “1358” is not suitable for early sowing in the Yangtze River Basin,and the suitable sowing time could be in the early October.the medium-and late-maturing varieties can achieve its yield potential under the condition of early sowing,and the suitable sowing time could advance to in the middle of September.Due to the high harvest index of early-maturing variety,the yield performance was better than that of medium-and late-maturing varieties under late sowing conditions.Therefore,in order to improve the yield,it is necessary to match suitable varieties and planting density under different sowing dates.Taking together,floral initiation of rapeseed was mainly regulated by the temperature and photoperiod in growth environment,and nitrogen fertilizer had no effect on it’s begining.Low temperature promoted the floral initiation of mid-and late-maturing genotypes through FLC,SOC1 and LFY signaling pathways.The growth and development model corrected by floral initiation data could quantify the thermal effect factor,vernalization effect factor and photoperiod effect factor of different maturing varieties,and combine historical meteorological data to accurately predict the yield.Matching different photothermal characteristics genotypes and sowing dates could provide guidance for decision-making in rapeseed production.The number of floral buds and flowers were significantly related to the yield of rapeseed.Exploring how to increase the number and reduce the degradation of reproductive organs is one of the important managements to increase the yield of rapeseed in the future. |
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