Abstract: 【Objective】The objective of the study is to investigate the effect of wheat straw-residue with field and nitrogen applications on the formation of branches and spikelets of hybrid japonica rice with large panicle.【Method】 A field experiment was conducted with the two applications of wheat straw to field (no wheat straw residue applied to field, T0; all wheat straw residue applied to field, T1) and three nitrogen (N) rates ( 225 kg·hm^-2, N1; 300 kg·hm^-2 , N2; 375 kg·hm^-2 , N3) by using the hybrid japonica rice cultivar, Yongyou 1540 as material. 【Result】 All wheat straw residues applied to field could increase the yield, but not significantly. N rates significantly influenced the yield, and at the N rate of 300 kg·hm^-2 the yield was significantly higher than at the N rate of 225 and 375 kg·hm^-2. The branch and spikelet formation of large panicle hybrid rice varied with their position at a whole rice panicle. The wheat straw and N rates significantly influenced the formation of the branches and spikelets. Compared with T0, the number of differentiated and retrograded total branches and spikelets were all significantly decreased under T1, and the retrograded number decreased more than the differentiated, resulting in the survived number being higher than those under T0. The wheat straw did not significantly affect the formation of the primary branches, but significantly affected the formation of the secondary branches and spikelets. N rates significantly affected the primary and secondary branches and spikelets. The number of differentiated and survived total branches and spikelets at the N rate of 300 kg·hm^-2 were highest among three N rates, while the retrograded number and percentage were lowest. Under the treatment of T0N2, the number of differentiated branches and spikelets were highest, but the number of retrograded branches and spikelets under T1N2 treatment were significantly higher than other treatments, which indicated that the survived number were highest. The wheat straw and N rates did not significantly affect the primary and secondary branches and spikelets at the upper part of a panicle, but significantly affected the formation of the branches and spikelets at the middle and basal part. It is worth noting that the differentiation and degradation of secondary spikelets at the basal part greatly affected the formation of the total spikelets. The survived primary or secondary branches and spikelets were significantly positively correlated with the yield and grain number per panicle. The differentiated and survived branches and spikelets were negatively correlated with the productive panicle number and seed setting rate, but significantly positively correlated with  1 000- grain weight.【Conclusion】There was a difference on the formation rules of branches and spikelets at the different parts of a panicle of the hybrid japonica rice with large panicle. The wheat straw and N rates significantly affected the formation of the branches and spikelets, especially the secondary branches and spikelets at the middle and basal part. The interaction effects existed between the wheat straw-residue applied to field and N rates. All wheat straw-residues applied to field and optimum nitrogen rates were conducive to the formation of branches and spikelets.

Key words: large panicle hybrid japonica rice, wheat straw-residue applied to field, nitrogen application, branches and spikelets formation, difference of parts in a rice panicle