Relationship between Panicle and Stem Growth and Spikelets per Panicle in Late-Maturing Medium Japonica Rice

Because spikelets per panicle is determined by the process of panicle differentiation,it is necessary to investigate their relationship.In this research,we employed two japonica rice cultivars(Wuyujing 3 and 86 you 8) to explore the relationships between both panicle and stem growth and spikelets number per panicle during rice panicle differentiation period by performing three panicle fertilizer treatments(NH,NM,and NL) in pot experiment.Samplings were made one time every 4 days.The results were as follows: The younger panicle grew slowly at the early stage of panicle differentiation(i.e.bud and branch differentiation stage) as compare with the base internodes of stem,which syncing with young panicle in growth.The competitive ability of younger panicle for assimilation was weaker than that of stem at the early stage.The growth rate of younger panicle of 86 you 8(with more spikelets per panicle,MP) at the early stage was lower than that of Wuyujing 3(with few spikelets per panicle,FP).From the meiosis phase on,panicle grew rapidly,and the third internode from top elongated at the same time,the weight ratio of spike/stem increased gradually,panicle got more nutrient than internodes,and compared with the FP cultivar,the MP cultivar had lager weight ratio of panicle to internodes.The time of younger panicle differentiation in 86 you 8 at early stage was 4 days lengthen than that in Wuyujing 3.Younger panicle grew rapidly from 16 days before heading.The weight ratio of panicle/stem for 86 you 8 was larger than that of Wuyujing 3.The fresh weight of panicle and stem at heading stage was correlated positively to spikelet number per panicle;and the weight ratio of diurnal increases of panicle/stem from 4 to 16 days before heading was correlated to the spikelet number per panicle significantly.The more rapidly the panicle weight increased under enough N,the more spikelet number increased during this stage.