Effects of Spikelet and Grain Positions on Grain Number,Weight and Protein Content of Wheat Spike

Grain development on wheat spike is asynchronous. The grain number,weight and protein content in different spikelet positions significantly varied with wheat cultivars and nitrogen levels. The experiment with two cultivars and two nitrogen levels was conducted at Nanjing from 2000 to 2001. The results showed that grain number,weight and protein content in different spikelet positions showed parabolic changes. The differences of the 3 parameters were larger in the cultivar with more grains on spike under different nitrogen levels,compared with the cultivar with fewer grains on spike,and the differences between cultivars were reduced with increasing nitrogen application. The effects of spikelet and grain positions on the weight,protein content and protein weight of individual grain varied with the grain number of spikelets. For 2 grain-set spikelets,the grain weight,protein content and protein weight in the first grain (1 st) position were higher than that in the second grain position (2 nd) (Fig.7,13). For the basic 3 grain-set spikelets,grain weight in 2 nd position was the highest,followed by that in 1 st and the third grain (3 rd) positions while grain weight in 1 st position≥that in 2 nd positionthat in 3 rd position for the top 3 grain-set spikelets. The individual grain protein content for 3 grain-set spikelets showed 2 nd position 1 st position 3 rd position (Fig. 8,14,18). For 4 or 5 grain-set spikelets,the grain weight in 2 nd position was the highest,followed by that in 1 st,3 rd and the fourth grain (4 th) positions and grain weight in the fifth grain (5 th) position was the smallest,while the individual grain protein content decreased with the increasing of grain positions (Fig. 9,10,15,16,19,20). In conclusion,the variation of the second grain position was a major factor for determining the effects of spikelet and grain positions on grain set and matter accumulation under different conditions. Grain number of each spike depended on the fecundity of basic spikelets,while grain weight,protein content and protein weight depended on the dry matter accumulation in grains of top spikelets. For different wheat cultivars with similar ear length but different grain number and protein content,the cultivars with more grain number showed more sensitivity to nitrogen application level. Interaction of genotype and nitrogen application determined the variation of grain number and matter accumulation on the wheat spike.