关键词: 油菜, 播期, 密度, 抗倒性, 产量

Abstract:

【Objective】Stem lodging is an important factor that restricts the increase of rapeseed production efficiency in China. The purpose of this study was to investigate the changing discipline and physiological mechanism of the lodging resistance of rapeseed stem treated with different sowing dates and densities, so as to provide theoretical and technical supports for high-yield and lodging resistance of rapeseed cultivation. 【Method】A split-plot experiment with two canola varieties (Huayouza 62 and Fengyou 520), two sowing dates (September 25, October 25) and four densities (15×10⁴, 30×10⁴, 45×10⁴, and 60×10⁴ plants/hm²)was performed to investigate yield and yield composition, stem mechanical strength, lodging index, microstructure, the main components of stem and key enzyme activities of lignin synthesis. 【Result】(1) At the sowing date of September 25 (T1), yield per plant, effective pods per plant and seeds per pod decreased with the density increased from 15×10⁴ hm^-2 to 60×10⁴ hm^-2, and the highest yield with the lowest lodging index was observed at density of 45×10⁴ hm^-2; Under the delayed the sowing date to October 25 (T2), the population yield, yield per plant, effective pods per plant and seeds per pod decreased significantly compared with those under T1, but the above-ground fresh weight decreased more significantly, resulting in the decrease of lodging index and the increase of lodging resistance under delayed sowing dates; (2)When sowing at the appropriate time, both the plant height and stem dry weight decreased significantly, while the lodging index was with a tendency of increasing firstly and then decreasing with increased densities, and the susceptible lodging part was transferred from the upper part to the base part of rapeseed stem. The parameters such as vascular bundle length/the thickness outside the pith and vascular bundle area/stem cross-sectional area gradually increased, and the content of lignin and cellulose of stem increased first and then decreased. With sowing dates delayed from September 25 to October 25, plant height, stem dry weight, stem lignin and cellulose content decreased significantly, but the above-ground fresh weight decreased more, resulting in the decreased lodging index. Stepwise regression analysis showed that lignin was the key index to improve the structure of the transport tissue, coordinate the lodging index and the population yield. The higher lignin content and the population lignin content of the stem could simultaneously obtain stronger lodging resistance of the stem and a higher population yield. (3) When the density increased from 15×10⁴ hm^-2 to 60×10⁴ hm^-2, the activities of peroxidase (POD), cinnamyl alcohol dehydrogenase (CAD), phenylalanine ammonia lyase (PAL) and 4-coumaryl: CoA ligase (4CL) under T1 increased, and those decreased significantly with sowing date delayed from T1 to T2. 【Conclusion】Optimizing planting density under different sowing dates could significantly increase the population yield, and the decreased yield at the delayed sowing date could be compensated by increasing planting density. The ability of lignin synthesis enhanced, and the lignin content increased under delaying sowing dates with higher plant densities, and coordinated the contradiction between high yield and lodging resistance in rapeseed.

Key words: rapeseed, sowing date, planting density, lodging resistance, yield