Increasing the concentration of film antitranspirant increases yields of rapeseed under terminal drought by improving plant water status

Film antitranspirant (AT) can effectively reduce yield losses of rapeseed crops under drought by blocking stomata if applied at the critical stage. However, the physiological mechanism by which film AT mitigates drought damage remains unclear. To investigate the effect of different concentrations of AT from 1% to 3% on rapeseed yields and its components of rapeseed under terminal drought, we carried out two field experiments at two locations in the year 2021, using rain shelters to simulate terminal drought at Bird's Nest (BN) and Flat Nook (FN). The study was conducted in a randomised complete block design with different concentrations of film AT (Vapor Gard, a.i., di-1-p-menthene) from 0% to 3% applied at the flowering stage of water-stressed rapeseed. Soil and plant water status, leaf gas exchange, seed yield and yield components, etc., were examined. Drought depressed leaf gas exchange and resulted in large yield losses. Aboveground biomass, seed yield, pod number and oil yield showed linear increases with AT concentrations consistently from both sites. With every 1% increase in concentration, seed yield was predicted to increase by 0.61 and 0.23 t ha-1 at BN and FN, respectively. The improvement in seed yield was strongly associated with pod number (R2 = 0.97 and 0.76, respectively; p < 0.001). Further, pod number and leaf relative water content were positively correlated, albeit with differences between the two sites. It was concluded that increasing concentrations can enhance yield benefits of film AT on rapeseed subjected to drought, and the greater yield from film AT appeared to be mediated through the improvement in leaf water status. As high concentrations of film AT are less cost-effective and conventional spraying methods only cover the adaxial surface, improving leaf coverage considering both sides of the leaf surface would help lower the cost and extend the commercial use of film AT.