Density-Tolerant Rapeseed Increased Population Yield by Enhancing Post-Anthesis Nonstructural Carbohydrate Translocation Efficiency in Stem

The stem nonstructural carbohydrate translocation efficiency could affect crop yield and lodging. However, the relationship between yield, lodging, and nonstructural carbohydrate transportation under high-density planting in rapeseed remains unclear. Therefore, field experiments with six varieties and two densities were conducted in 2020-2022 to investigate the effects of planting density on rapeseed yield, the limiting factors for yield increase under high-density planting, and the photosynthetic carbon metabolism characteristics of typical dense-tolerant materials. Results showed that: (1) As density increased, the yield of C31 (tall plant) significantly increased while that of N91 (short plant) significantly decreased with the largest decrease rate during the two growing seasons. The lodging index significantly increased as well under high density. Among the six varieties, the lowest lodging angle and stem lodging index of the upper parts were C31. (2) High-density planting reduced chloroplast density and chloroplast size, net photosynthetic rate, and enzyme activities of photosynthetic carbon metabolism. It also decreased starch content in leaves, stems, and siliques as well as the nonstructural carbohydrates (NSC) transport amount and rate in stems. The NSC transport volume and transport rate in stems were significantly positively correlated with yield per plant and negatively correlated with the lodging index. (3) Under high-density planting, the NSC translocation rate and translocation amount in stems for C31 were significantly greater than those for N91. The density-tolerant material C31 had greater individual yield and lodging resistance as greater above-ground dry matter accumulation, stronger photosynthetic carbon metabolism, and NSC transport abilities under high-density planting.