Metabolic and film antitranspirants both reduce drought damage to wheat yield despite having contrasting effects on leaf ABA

Film antitranspirants (e.g. di-1-p-menthene) and metabolic antitranspirants (e.g. exogenous ABA) can be used to protect grain crops from drought, particularly during reproductive development. Here, we compared effects of di-1-p-menthene (1.0 L/ha) and exogenous ABA (100 µM) on well-watered and droughted spring wheat in two glasshouse experiments. Progressive drought was imposed in the first experiment, controlled drought in the second, both from flag leaf emergence. Antitranspirants were applied at flag leaf emergence, except in the controlled drought experiment where additional ABA applications were made at four further stages up to anthesis-complete. Measurements were taken for endogenous ABA, stomatal conductance and photosynthesis during reproductive development, and yield components at maturity. Both progressive and controlled drought elevated leaf ABA, less so in di-1-p-menthene-treated plants, whereas in exogenous ABA-treated plants leaf ABA was elevated further. Overall, both antitranspirants improved yield under reproductive-stage drought, more so for controlled drought. Grain yield was negatively associated with reproductive-stage leaf ABA concentration except that raising leaf ABA concentration with multiple exogenous ABA applications was associated with high yield. In conclusion, both antitranspirants generally reduced effects of reproductive-stage drought on yield despite having contrary effects on leaf ABA