A laboratory procedure was used to evaluate saline tolerance of pistachio rootstock species. Results were compared to those from a 2-year, outdoor lysimeter study to test reliability of the method. Excised root tips from seedlings of Pistacia atlantica Desf., P. terebinthus L. (two selections), and P. integerrima Stewart × atlantica (Pioneer Gold II, or PG II), were exposed to laboratory solutions that simulated soil solution electrical conductivity (EC) and Na: Ca ratios in the lysimeters. Following 24 hours of incubation, the efflux of ultraviolet (UV)-absorbing solutes was measured, providing an indication of cell membrane permeability. Leakage occurred with saline solutions comparable to lysimeter soil water salinity that increased leaf Na concentrations and decreased average root growth (175 mm NaCl with 12.5 mm Ca, or EC of 18.1 dS·m-l). Cell injury increased linearly with salinity (R2 = 0.81) and was highest in root tips of a P. terebinthus selection having least Na exclusion capability in the lysimeters. On average, these excised roots lost 38% more solutes than roots of a stronger Na-excluding genotype. There were no differences in leakage responses of the other species and selections. Leakage intensity was independent of various stress media, including isosmotic CaC12, mannitol, and the simulated Na/Ca mixtures in molar ratios of 10:1 to 20:1. With no Ca, however, damage caused by isosmotic NaCl was 76% to 87% higher, indicating that for these species, the Na: Ca ratio can alter root cell membrane permeability. Correlation between long-term observations in the lysimeters and leakage occurrence in the laboratory indicates that solute leakage tests with roots may aid in characterizing Pistacia spp. rootstocks for saline condition.
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