Effect of paclobutrazol and calcium on increasing of chilling tolerance of pistachio seedlings and trees

To investigate the effects of paclobutrazol, calcium (Ca), and temperature treatment (cold) on resistance to chilling of pistachios seedlings (Akbari cultivar), a factorial greenhouse experiment was carried out in a completely randomized design with three replications. The treatments included paclobutrazol (0, 75, and 150 mg.-1), Ca (0, 3, and 6 g.l-1 of calcium chelate source) and temperature (0,-2, and -4 in the greenhouse and 0, -2, and +4 °C in the garden). The results showed that with decreasing temperature, total chlorophyll, carotenoids decreased, but the combined use of paclobutrazol and Ca increased the amount of these parameters compared to the control. Also, with decreasing temperature, the amount of electrolyte leakage increased, while using of paclobutrazol and Ca reduced the amount of this parameter compared to control seedlings. Measurement of osmotic regulatory parameters showed that the concentration of starch and soluble protein in leaves decreased with decreasing temperature. However, with the combined use of paclobutrazol (150 mg.l-1) and Ca (6 g.l-1) at -4 ° C, the concentration of proline, total phenol, soluble sugars, starch and soluble protein were increased compared to the control by 112, 28, 20, 80, and 196% respectively. The results of the garden experiment also showed that with decreasing temperature, the amount of ion leakage, in the control fruits increased. Application of paclobutrazol and Ca treatments reduced electrolyte leakage, so that the lowest percentage of electrolyte leakage was observed at -4, 0, and -2 °C when paclobutrazol and Ca were used simultaneously and at the highest levels and the electrolyte leakage rate decreased by 27, 12, and 38% compared to control fruits, respectively. Finally, the results of this study showed that the combined use of Ca and paclobutrazol can reduce the damage caused by chilling in seedlings and pistachio trees.