Varietal differences in stem assimilate translocation and lodging resistance of rice under reduced nitrogen input

The low translocation rate of stem assimilates and lodging under high nitrogen conditions are major factors limiting the realization of the yield potential of rice. The objectives of this study were to (1) determine the characteristics of stem nonstructural carbohydrates (NSCs) translocation and lodging resistance in different types of rice varieties and (2) elucidate the responses of stem NSCs translocation and lodging resistance to reduced nitrogen (RN) input. Field experiments were conducted using four types of rice varieties with two nitrogen levels, including normal nitrogen (NN, namely, farmer's practice, 225 kg N ha⁻¹ for indica conventional and indica hybrid rice and 300 kg N ha⁻¹ for japonica conventional and indica–japonica hybrid rice in Jiangsu Province, China) and 20% RN (180 and 240 kg N ha⁻¹, respectively). The results showed that there were significant differences in the stem NSCs translocation and lodging index of the basal stem among different types of varieties; indica hybrid rice was the highest, followed by indica conventional rice and indica–japonica hybrid rice, while japonica conventional rice was the lowest. The high activities of α-amylase, β-amylase, and sucrose phosphate synthase may contribute to high stem NSCs translocation. Correlation analysis revealed that NSCs translocation was significantly positively correlated with 1000-grain weight, grain yield, and lodging index, while it was significantly negatively correlated with dry weight/length, dry weight/volume, and bending stress of the basal stem. Compared with NN, RN significantly improved NSCs translocation and had no significant effect on the lodging resistance-related traits of the basal stem or grain yield. Therefore, this research indicates that a 20% reduction in nitrogen input can maintain grain yield by enhancing stem assimilate translocation without lodging resistance reduction and consequently synergizing nitrogen reduction, high yield, and lodging resistance.