Effects of uniconazole rate on agronomic traits and physiological indexes of rapeseed blanket seedling

Mechanized transplanting of rapeseed (Brassica napus L.) blanket seedling is an innovative cultivation technology. Cultivating high quality blanket seedling to ensure high survival rate of seedling after transplanting is the key of the technology. The effects of different uniconazole rates of 0, 0.5, 1.0, 1.5 and 2.0 mg/tray, spraying at one leaf and one heart stage, on selected agronomic traits, physiological indexes and survival rate of two rapeseed cultivars (‘Qinyou 10′ and ’Yangyou 9′) were investigated in 2018 and 2019. Our results showed that the plant height decreased significantly with the increase of uniconazole rate. However, the collar diameter increased significantly with the increase of uniconazole rate up to 1.5 mg/tray, and the leaf area, dry weights of root and shoot increased with increased uniconazole rate up to 1.0 mg/tray. The root to shoot ratios, N concentrations of root and shoot with the uniconazole rates of 1.0 and 1.5 mg/tray were higher than those with other treatments. As uniconazole rate increasing, gibberellin (GA) and auxin (IAA) concentrations of root and shoot decreased, while abscisic acid (ABA) concentrations increased, and cytokinin (CTK) concentrations topped at uniconazole rate of 1.0 mg/tray and decreased thereafter. The seedling survival rates with 1.0 and 1.5 mg/tray were greatly higher than those in other treatments. Regression analysis suggested plant survival rate was positively related to CTK concentrations and negatively to GA concentrations of root and shoot. To achieve high survival rate after mechanized transplanting, our study revealed that the uniconazole applied at a rate of 1.0 mg/tray was recommended as the best, followed by 1.5 mg/tray. The findings would help to enhance qualities of rapeseed blanket seedling and to promote popularization of mechanized transplanting of rapeseed production.