Diverse responses among wild banana species to vapour pressure deficit, a solution for drought tolerance breeding?

The predicted rise in global temperature is not only affecting plant functioning directly, but is also increasing air vapour pressure deficit (VPD). The yield of banana is heavily affected by water deficit but so far breeding programs have never addressed the issue. A reduction in transpiration at high VPD has been suggested as a key drought tolerance breeding trait to avoid excessive water loss, hydraulic failure and to increase water use efficiency. In this study, stomatal and transpiration responses under increasing VPD at the leaf and whole-plant level of 8 wild banana (sub)species were evaluated, displaying significant differences in stomatal reactivity. Three different groups were identified under increasing VPD. M. acuminata spp. e rrans (group I), M. acuminata spp. zebrina (group II) and M. balbisiana (group II) showed the highest transpiration rate limitations to increasing VPD. In contrast to group I, group II only showed strong reductions at high VPD levels, limiting the cost of reduced photosynthesis and strongly increasing their water use efficiency. Group II genotypes thus show favourable responses for high water use efficiency in regions with high VPDs. This provides a basis for the identification of potential parent material within their wild populations for drought tolerance breeding. Highlight Wild banana species respond significantly different to water deficit caused by VPD increases and differ in the rate of stomatal reduction, revealing opportunities for drought tolerance breeding. ### Competing Interest Statement The authors have declared no competing interest. * A : photosynthetic rate Amax : maximally measured photosynthetic rate Ameas : measured photosynthetic rate ABA : abscisic acid Erate : transpiration rate Emeas : measured transpiration rate Epred : predicted transpiration rate Eq : equation gs : stomatal conductance h : hour ITC : International Transit Centre kPa : kilopascal L : liter LA : leaf area m : meter min : minutes mol : moles m tot : total weight PC : principal component s : seconds se : standard error ssp : subspecies R2 : R-squared t1 : timepoint 1 t2 : timepoint 2 VPD : vapour pressure deficit VPDleaf : leaf-to-air vapour pressure deficit iWUE : intrinsic water use efficiency µmol : micromoles ϕE : transpiration reduction ϕstom : stomatal reduction