Yield improvement with antitranspirant application in droughted wheat associated with both reduced transpiration and reduced abscisic acid

In Mediterranean-type climates, terminal drought induces grain yield losses in wheat. Antitranspirants can reduce the impacts of terminal drought and improve yield, but the mechanisms involved are not fully understood. Among other impacts, drought elevates endogenous abscisic acid (ABA) concentration. Here, the effectiveness of a film antitranspirant (di-1-p-menthene) was studied in relation to plant water status and spike ABA. The objective was to determine whether drought amelioration with di-1-p-menthene was solely mediated through a reduction in ABA by comparing its effects to that of fluridone (an ABA inhibitor). The treatments were assessed in a randomized complete block design in two field experiments in spring and summer of 2020, with six and eight replicate blocks, respectively, at Harper Adams University, UK, to compare their effects on spike ABA, gas exchange and agronomic traits under progressive drought conditions. Di-1-p-menthene was applied at 1 l/ha; and fluridone at 10, 20 and 50 μM concentrations, at flag leaf emergence, growth stage 37 (GS37). Drought increased spike ABA and downregulated photosynthesis. Di-1-p-menthene and fluridone at some concentrations, reduced spike ABA and photosynthesis. Di-1-p-menthene suppressed transpiration and spike ABA, each by 21% but increased grain yield by 27%. In contrast, although fluridone (at 10 and 50 μM) also reduced spike ABA (by 16%), overall, it did not alter transpiration or grain yield. The results suggest that yield improvement with di-1-p-methene is mediated through mechanisms that involve conservation of plant water linked to reduced transpiration, with inhibition of spike ABA playing a secondary role.