Soaking seeds with paclobutrazol enhances winter survival and yield of rapeseed in a rice-rapeseed relay cropping system

Rice-rapeseed relay cropping is an effective way to use winter fallow fields and increase land use efficiency. However, the overlapping period of 10–15 days for rice-rapeseed cultivation results in reduced winter survival and less yields. Therefore, in this study, we investigated if the treatment of oil rape seeds with paclobutrazol (PAC) improves its winter hardiness and yields by altering its crop morphology. First, a pot experiment was conducted to determine the appropriate PAC concentration to soak seeds upon seedling growth and the germination rate. Another pot trial was performed to check the responses of different rapeseed cultivars to the proposed treatment. Rapeseed was cultivated in no-tillage rice fields at an experimental site in Wuhan from 2009 to 2011. In the absence of PAC treatment, rapeseed sown in pots and rice fields showed excessive elongation of the crown, which resulted in low yields and yield-related traits at maturity. Soaking seeds in PAC improved seedling growth, seedling survival and crown diameter, but decreased the crown length during winter. The most effective concentration of PAC was 4 mg/L and higher concentrations significantly reduced seed germination rates. Our results demonstrated that rapeseed sown in rice fields after the seeds had been soaked with PAC improved seedling quality at the wintering stage and yield at maturity.