Response of major restore lines for hybrid rice to nitrogen rate in Sichuan Province

Objectives Nitrogen is one of the most important factor in rice growth that significantly affects the formation of rice quality. To make clear the effect of different nitrogen levels on rice quality and understand the sensitivity to nitrogen of different varieties can provide a basis for high quality breeding and scientific fertilization of rice.

Methods A two factors’ split plot experiment was designed to assess the effect of nitrogen rates (N 0, 90 kg/hm² and 180 kg/hm²) on milling, appearance, cooking and eating qualities of 15 restore lines and one hybrid rice variety (Yixiangyou 2115), and investigated the sensitivity of nitrogen in the test by clustering analysis.

Results 1) The nitrogen rates had significant effect on milling and appearance qualities of rice restore lines. No significant differences in the milled rice rate and length/width ratio were observed with the increase of nitrogen rate. However, the brown rice rate and head rice rate were obviously increased, compared to the N0 treatment, 0.8% and 1.4% increases in brown rice rate, and 5.7% and 7.9% increases in head rice rate were observed by N90 and N180, but the chalky area ratio and chalkiness grain rate were decreased with more nitrogen. Compared to the N0 treatment, 26.1% and 55.0% falling in the chalky area ratio, and 12.6% and 32.8% falling in chalkiness grain rate were observed by N90 and N180. 2) Starch RVA characteristics were significantly influenced by the nitrogen rates. The peak viscosity, hot paste viscosity, cool viscosity, consistence viscosity and amylose content were obviously decreased with the increase of nitrogen rate. 3) Cluster analysis showed that the sensitivity of restore lines varied to the nitrogen rate. At N90, the restore lines were classified into three classes, nitrogen sensitive type including Lehui188, Chenghui727 and Huhui602; nitrogen middle type including Mianhui725, Huhui17, Mianhui523 and Xikehui768; and nitrogen slow type including Minghui63,Duohui1, Chenghui838 (718, 3203), Yahui2115, Shuhui498 (527) and Yixiangyou2115. At N180, the restore lines were classified into three classes, nitrogen sensitive type including Lehui188, Mianhui725, Huhui17 and Xikehui768; Nitrogen middle type including Minghui63, Duohui1, Shuhui498 (527) and Yixiangyou2115, and nitrogen slow type including Yahui2115, Chenghui3203 (838, 718, 727), Mianhui523 and Huhui602.

Conclusions The increase of nitrogen rate can effectively improve the rice milling and external quality, and regulate the RVA profile characteristics of rice starch of restore lines in Sichuan province. Yahui2115, Chenghui3203 (838, 718, 727), Mianhui523 and Huhui602 had better quality, and their quality was changed by nitrogen rate change in sensitive nitrogen species. And there were litter changes in rice quality under the low nitrogen condition. Sensitive nitrogen species include Lehui188, Mianhui725, Huhui17 and Xikehui768 whose rice quality could be improved by increasing nitrogen levels. Nitrogen intermediate species include Minghui63, Duohui1, Shuhui498 (527) and Yixiangyou2115.