Effects of Rootstock on Water Stress, Physiological Parameters, and Growth of the Pistachio Tree

In Spain, almost all pistachios are grown under water-stress conditions. Pistachio plants have sophisticated mechanisms to avoid or tolerate stress. It is known that the rootstock affects responses to water stress in the cultivar grafted onto it. The traditional belief is that Pistacia terebinthus L. is the rootstock best adapted to rainfed conditions. This study examined the effect of rootstock on stress traits, photosynthetic rate, transpiration, stomatal conductance, chlorophyll, polyphenol concentrations, and growth in plants of Pistacia vera L. cv. Kerman grafted onto P. terebinthus, P. atlantica, and UCB-1. These responses were classified into constituent traits and characteristics of the plant's adaptation to water stress. The latter was induced by adding PEG 6000 to the nutrient solution. Plants grafted onto P. terebinthus showed more constituent traits, while plants grafted onto UCB-1 showed a greater number of drought-responsive traits. Plants grafted onto P. atlantica showed similar adaptative traits to those observed in UCB-1 but lower values of transpiration and net photosynthesis. Although it is likely that plants grafted onto P. terebinthus survive longer under extreme drought conditions, under moderate stress conditions, their yield is probably lower than that of plants grafted onto UCB-1 under the same moderate stress conditions.