Studies On The Yield Formation, Leaf Senescence And Root Morphology Under Different Planting Densities Of Oilseed Rape

Winter oilseed rape(Brassica napus L.), an important edible oil crop worldwide,which represents approximately 19.9% of the total oilseed production worldwide and89% of the oilseed yield in China. However, the seed yield has lagged behind the increasing demands driven by population growth. Moreover, oilseed rape must compete economically with cereal crops and meet this challenge. Increasing the seed yield per unit area was an effective approach to promote the fourth leap in the Chinese rapeseed industry. Thus, it is necessary to develop strategies to improve the expression of yield potential. Productivity at varying plant densities(27.0, 37.5, 48.0,58.5 and 69.0 plants hm-2) was studied by employing a conventional variety Zhongshuang 11(ZS 11) and a hybrid variety Zhongyouza 12(ZYZ 12). The main results are listed as follows:1. With the increase of plant density, seed yield and pod numbers per unit area presented an increase first, followed by a decrease. The treatments of five different plant densities(27.0~69.0 plants hm-2) were aimed to clarify the mechanism of productivity at varying plant densities in ZS11 and ZYZ12. The results indicated that the seed yield can be increased significantly by increasing the plant density to a certain extent. With the increase of the plant density, the seeds per pod significantly decreased.2. HD(planting density at 58.5 plants hm-2) showed a higher value than LD(planting density at 27.0 plants hm-2) in terms of green leaf area index, pod area index,pod photosynthetic rate, root length, root tips, root surface area and root volume per unit area at peak anthesis, suggesting that HD has better canopy structure and root morphology to achieve a high pods number per unit area.3. HD exhibited rapid decrease than LD in GLAI and green leaf numbers per plant and leaf photosynthetic rate. HD also showed higher MDA accumulation and chlorophyll contents than LD. The most important was that the accelerated leaf senescence accompanying with the high PAI and pod wall photosynthesis, whichcontributed to the high seed yield in HD.4. HD had a huge root system at peak anthesis and produced a larger reduction in all root characteristics to make full use of the population dominance.5. The present results also showed that higher dry matter accumulation and nitrogen utilization efficiency after peak anthesis in HD were partially responsible for the high seed yield.It can be concluded that the seed yield of winter oilseed rape can be increased significantly by increasing plant density to a certain extent(27.0~58.5 plants hm-2),mainly due to the increased pod numbers per unit area, and there is still much room for improvement for seeds per pod at high plant densities. Thus, the high yield in HD might reflect the harmonious alteration between leaf senescence and better radiation distribution in the pod canopy with a moderate number of pods from main inflorescences and branches. Higher NHI and nitrogen utilization efficiency in HD were mainly attributed to the lower leaf area duration after peak anthesis. These results suggested that increasing the plant density within a certain range was effective for high seed yield in winter rapeseed in China in the modern cultivation system.