Stomatal response and intrinsic water use efficiency of three pistachio cultivars grown in Central Spain: a relevant criterion for plant selection

There is little information describing varietal responses of pistachio trees to water stress, as previous works have been focused on rootstocks disregarding scion influences on tree water relations. Nevertheless, the evaluation of the mechanisms adopted by pistachio cultivars to deal with drought is essential for efficient cultivar selection. This study assessed, over 2 years, the relationship between midday stem water potential (Ψ<inf>s</inf>) and leaf stomatal conductance (g<inf>s</inf>) of three pistachio cultivars (Golden Hills, Lost Hills, and Kerman) grown in Central Spain under the same conditions. Soil water content, leaf osmotic potential at full turgor (Ψ<inf>os</inf>), net photosynthesis rate (P<inf>n</inf>), and intrinsic water use efficiency (WUE<inf>i</inf>) were measured. The lowest Ψ<inf>s</inf>, Ψ<inf>os</inf>, g<inf>s</inf> and P<inf>n</inf> values were observed in Kerman; however, this cultivar registered the highest WUE<inf>i</inf> values. In general, g<inf>s</inf> values were greater than 200 mmol m⁻² s⁻¹ when Ψ<inf>s</inf> was greater than −0.8 MPa in Kerman, −1.3 MPa in Golden Hills, and −1.4 MPa in Lost Hills. The relationships between Ψ<inf>s</inf> and g<inf>s</inf> were significant for the three cultivars, but the slopes of the regression lines differed among them. These findings reflected the distinct stomatal response of these pistachio cultivars and suggest that Kerman has stricter stomatal control.