| As Chinese multiple cropping system is fundamentally different from developed countries’ single cropping system, we need early maturing rapeseed to deal with the seasonal conflict between rape and rice in practical production. Additionally, it is easy to cause heat forced maturity by the temperature booming from April to May in southern China and both thousand seed weight and oil content are decreased. Early maturing rapeseed can not only completely solve the seasonal contradiction and the problem of making full use of the fallow fields, but also can avoid or reduce the harm from heat forced maturity and the dry hot wind at the late growth stage. At the same time, it is easy to get the ideal plant type and population with characteristics of dwarf, lodging resistance and less branching through optimization of cultivation and management measures. The research on early-maturing rapeseed varieties currently mainly focuses on the inheritance of earliness and early maturing variety breeding, whereas the research on physiological and biochemical characteristics, organ formation mechanism and yield potential are fewer. Therefore, it has a great significance to guide early maturing rapeseed breeding and high yield cultivation practice to ascertain rape early mechanism, put forward the effective regulate and control measures and form matched high-yielding cultivation techniques. In this study, we selected three varieties(early-maturing variety 1358, mid-maturing variety Zhongshuang 11 and late-maturing variety Zheshuang 8) and designed three different sowing dates(15th September, 30 th September and 15 th October) to research the early-maturing rapeseed growth process, dynamic changes of nutritional organs, quantity changes of flowers, yield and its component factors changes and changes of endogenous hormones in late seedling stage, the main results are as follows:1. Growth period: the result showed that growth period of early-maturing rapeseed was shorter than mid and late maturing rapeseed. Seedling stage of early-maturing rapeseed was shorter while flowering and pod periods were longer than the mid and late maturing rapeseed. With delay of sowing date, seedling stage of early-maturing rapeseed prolonged, but flowering and pod periods were shorter, and whole growth period of each variety was shorter. The time of budding, bolting, initial bloom and full bloom of early-maturing rapeseed were seriously influenced by sowing date, and delayed with the delay of sowing date.Therefore, it is suggested that early early-maturing rapeseed 1358 is suitable to be sowed in mid-October to avoid yield decrease caused by early flowering, while mid and late maturing variety should be early sowed to form higher nutritional organs.2. Flower bud differentiation period: duration of flower bud differentiation of early-maturing variety in each sowing date was shorter than the mid and late maturing varieties and prolonged by delay of rapeseed sowing, accumulated temperature of early-maturing variety in flower bud differentiation, budding and bolting were shorter than mid and late maturing varieties, so early maturing variety blossoms early, and grows much faster than mid and late maturing varieties before winter. Mid and late maturing varieties in whole sowing date and early-maturing variety in late sowing were influenced by the low temperature between 17 th December to 20 th February, so bolting time of them was significantly prolonged to avoid the phenomenon of early flowering.3. Nutritional organs: early-maturing variety vegetative organs, such as leaf and stem grows faster than mid and late maturing varieties, but flowering too early lead vegetative organs dry matter accumulation was lower, plant height, total leaf number, leaf weight and leaf area of early-maturing variety were generally lower than mid and late maturing varieties. Late sowing lead total leaf number of early-maturing variety increase but leaf weight and leaf area decrease. The time of stem rapid growth period, highest leaf weight and highest leaf area of early-maturing variety was delayed by delay of sowing date, indicates that late sowing can lead nutrients accumulation of early-maturing variety decreased and grow slowly.4. Quantity changes of flowers: early-maturing variety bloomed earlier and the duration of it was longer than mid and late maturing varieties sowed in mid and late September, and the quantity of flowers in first sowing date was significantly lower than in second sowing date and the same sowing date of mid and late maturing variety. The time of early-maturing variety flowering was delayed sowed in mid October, the duration of it was shorter and quantity of flowers decreased but not significantly. due to the low temperature before winter, early sowing often lead to slow growth and low quantity of early-maturing variety flowering, late sowing just can let the initial bloom stage of early-maturing variety avoid this low temperature.5. Yield and its component factors changes: yield and seeds per silique of early-maturing variety were generally lower but 1000 grains weight was higher than mid and late maturing varieties, pod number in main stem and branches of early-maturing variety were lower than mid and late maturing varieties in mid and late September, but higher in mid October. Properly late sowing can increase yield, main stem pod number and seeds per silique of early-maturing variety, but branches pod number and 1000 grain weight decrease.6. Endogenous hormones: in the late seedling stage, the levels of endogenous gibberellin(GA3) and zeatin riboside(ZR) in early-maturing variety were significantly higher than mid-maturing and late-maturing in each sowing date, but it was reverse to endogenous abscisic acid(ABA) and indoly lacetic acid(IAA). Late sowing led levels of endogenous GA3 and ZR decrese, but levels of endogenous ABA and IAA increase in early-maturing variety late seedling stage. To each sowing date of early-maturing variety, the level of GA3 reached the top in the middle of flower bud differentiation, the level of ZR reached peak in the early and late of flower bud differentiation, levels of ABA and IAA were very low in the early of flower bud differentiation but reached peak in the late of flower bud differentiation, and the level of GA3 in the whole late seedling stage was very high which sowed in mid and late September. To each sowing date of early-maturing variety, ratios of GA3/ABA and ZR/IAA were general higher but IAA/ABA were general lower than mid and late maturing variety; the ratio of GA3/ABA was very high and ZR/IAA reached peak in the early of flower bud differentiation, the ratio of GA3/ABA and IAA/ABA was very low and ZR/GA3 reached peak in the late of flower bud differentiation. |
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