Nitrogen Application Rate Affects the Accumulation of Carbohydrates in Functional Leaves and Grains to Improve Grain Filling and Reduce the Occurrence of Chalkiness

Changchun Guo; Xiaojuan Yuan; Fengjun Yan; Kaihong Xiang; Yunxia Wu; Qiao Zhang; Zhonglin Wang; Limei He; Ping Fan; Zhiyuan Yang; Zongkui Chen; Yongjian Sun; Jun Ma

doi:10.3389/fpls.2022.921130

Nitrogen Application Rate Affects the Accumulation of Carbohydrates in Functional Leaves and Grains to Improve Grain Filling and Reduce the Occurrence of Chalkiness

Front Plant Sci. 2022 Jun 24:13:921130. doi: 10.3389/fpls.2022.921130. eCollection 2022.

Authors

Changchun Guo^{1

2}, Xiaojuan Yuan^{1

2}, Fengjun Yan^{1

2}, Kaihong Xiang^{1

2}, Yunxia Wu^{1

2}, Qiao Zhang^{1

2}, Zhonglin Wang^{1

2}, Limei He^{1

2}, Ping Fan^{1

2}, Zhiyuan Yang^{1

2}, Zongkui Chen^{1

2}, Yongjian Sun^{1

2}, Jun Ma^{1

2}

Affiliations

¹ Rice Research Institute, Sichuan Agricultural University, Chengdu, China.
² Crop Ecophysiology and Cultivation Key Laboratory of Sichuan Province, Chengdu, China.

Abstract

Chalkiness, which is highly affected by nitrogen (N) management during grain filling, is critical in determining rice appearance quality and consumer acceptability. We investigated the effects of N application rates 75 (N₁), 150 (N₂), and 225 (N₃) kg ha^-1 on the source-sink carbohydrate accumulation and grain filling characteristics of two indica hybrid rice cultivars with different chalkiness levels in 2019 and 2020. We further explored the relationship between grain filling and formation of chalkiness in superior and inferior grains. In this study, carbohydrates in the functional leaves and grains of the two varieties, and grain filling parameters, could explain 66.2%, 68.0%, 88.7%, and 91.6% of the total variation of total chalky grain rate and whole chalkiness degree, respectively. They were primarily concentrated in the inferior grains. As the N fertilizer application rate increased, the chalky grain rate and chalkiness degree of both the superior and inferior grains decreased significantly. This interfered with the increase in total chalky grain rate and chalkiness. Moreover, the carbohydrate content in the functional leaves increased significantly in N₂ and N₃ compared with that in N₁. The transfer of soluble sugar from the leaves to the grains decreased the soluble sugar and increased total starch contents, accelerated the development of grain length and width, increased grain water content, and effectively alleviated the contradiction between source and sink. These changes promoted the carbohydrate partition in superior and inferior grains, improved their average filling rate in the middle and later stages, optimized the uniformity of inferior grain fillings, and finally led to the overall reduction in rice chalkiness.

Keywords: carbohydrate; chalkiness; dynamic accumulation; grain-filling; nitrogen.