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Abstract: This paper deals with the effect of spring climatic condition on the spikelet differentiation of winter wheat in the district Beijing The optimum temperature indexes for spikelet differentiation were found out. In early spring the more the number of days with daily vaerage temperature≤7.5℃ between single ridge and glume and≤10.5℃ from glume to the formation of terminal spikelet, the more farourable to spikelet differentiation.The indexes of accumulated temperature≥0℃ at the apperence of differentiation stages are 245 degree day for glume and 575 degree day for tetrad stage etc. This paper also discussed the relationship among the rate of spikclet differentiation and temperature or duration of differentiation and suggested three agroclimate year typesworm, cooland normal in spring, according to the effect of spring climatic condition on the spikelet differentiation of winter wheat

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