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一、水稻在进化历史上,自交为进化,在进化过程中形成的种子繁殖的遗传系统不依靠风(虫)传粉,是其适应性。杂交稻为异交,属退化,靠风传粉,结实率(全为制种产量)受各年风向和风速的影响而各异。二、杂交稻制种极烦,制种时要分期播种,使花期相遇,剪叶、剥苞、辅助授粉都麻烦。再者不易保纯,常发生异交串粉,三系易发生机械混杂。若三系不纯,则杂交稻必不纯。
First, the evolutionary history of rice, selfing as evolution, the genetic system of seed propagation in the evolutionary process does not rely on wind (insect) pollination, is its adaptability. Hybrid rice is outcrossing, belonging to the degenerate, rely on wind and powder, seed setting rate (all seed production) affected by the wind direction and wind speed in different years. Second, the hybrid rice seedy very annoying, planting seed to be staged, so that the flowering meet, cut the leaves, peel, assisted pollination are troublesome. Moreover not easy to pure, often occur cross-string powder, three-prone machinery mixed. If the three lines impure, the hybrid rice will be impure.