A drought screening experiment focusing on intrinsic water use efficiency (WUEi) was carried out among 132 clones belonging to a dihaploid potato mapping population. The clones were exposed to progressive soil drying during a five-day period in a greenhouse pot experiment. Analysis of the underlying variables was done based on a multivariate data analysis strategy. The strategy successfully divided the clones into WUEi performance categories. Differences between clonal WUEi responses were traced back to differences in the net photosynthetic rate. Stomatal conductance (g(s)) did not vary significantly between the clones. Leaf abscisic acid (ABA) concentration and leaf water potential were found to reflect known isohydric behaviour for potato, and a non-linear relationship could be established for g(s) and leaf ABA concentration across the WUEi groups. Similarly, a common non-linear relationship between leaf ABA concentration and soil water potential was found. The latter findings suggest that the investigated population did not harbour significant genetic variation as to ABA production as function of soil desiccation level or with respect to the sensitivity of stomatal aperture vis-a-vis leaf ABA concentration and soil water potential.
