Counter-Intuitive Increase in Yield From Film Antitranspirant Applied to Droughted Wheat.

Film antitranspirants are materials of low permeability to water vapour which can be applied to the leaf surface to limit water lost through transpiration and therefore delay the detrimental effects of desiccation. Since they are also of low permeability to carbon dioxide, photosynthesis to produce the assimilate for crop yield is also reduced. Thus the conventional reductionist view, based on extensive research on the physiology of transpiration and photosynthesis in the mid to late 20^th century, is that these materials are of limited utility, mainly on ornamentals in situations where photosynthesis is not important. In our research we have used a more holistic approach which recognises the varying sensitivity of yield-forming processes in small-grain cereals to water loss depending on the development stage of the crop. Thus we propose the hypothesis that the most sensitive stage of yield formation may respond positively to antitranspirant  application through reduced water loss irrespective of reduced assimilate availability from photosynthesis. Here we show that film antitranspirant applied at more-sensitive stages increases yield, whereas applied at less-sensitive stages it reduces yield. Field experiments were conducted with wheat grown in drought conditions over three years. Yield response to film antitranspirant application was linearly related to crop development stage at the time of application. Yield was reduced when antitranspirant was applied between half inflorescence emerged to anthesis complete, as expected from the paradigm developed from the previous research. In contrast, when antitranspirant was applied between flag leaf visible to boots swollen stages yield increased in contradiction of the prevailing paradigm, but consistent with our hypothesis. These results show that in small-grain cereal crops, which are major contributors to global food supply, film antitranspirants have potential for mitigating effects of drought on yield.