Control of hyperhydricity of Pistacia khinjuk stocks in vitro shoots.

Hyperhydricity is the most extensive physiological disorder during in vitro propagation. This disturbance can induce anatomical, morphological and physiological problems that cause serious damage. The factors that cause hyperhydricity are the composition of nutrient media and cultures conditions. To reduce the hyperhydricity of Pistacia khinjuk, ammonium nitrate (NH₄NO₃), calcium chloride (CaCl₂·2H₂O), cytokinins of meta-topolin (mT) and 6-benzylaminopurine (BAP) at different concentrations were investigated in Murashige and Skoog (MS) medium. The lowest percentage of hyperhydricity (34.30%) were obtained from the medium containing 1650 mg/L NH₄NO₃, 110 mg/L CaCl₂·2H₂O and1 mg/L mT; the highest percentage of hyperhydricity (68.42%) were obtained from the medium containing 206.25 mg/L NH₄NO₃, 440 mg/L CaCl₂·2H₂O and 0.5 mg/L BAP. The maximum average number of shoots per explant (2.45), average shoots length (18.47 mm) and proliferation rate (85%) were obtained from the medium containing 1650 mg/L NH4NO3, 110 mg/L CaCl2·2H2O of MS and 1 mg/L mT. In addition, when soluble protein (2.12 mg/g) and total chlorophyll a, b (0.96 mg/g) value of normal (non-hyperhydric) shoots were higher than hyperhydric shoots, carotenoid (11.75 µg /g) and water content (78.70%) value of normal shoots were lower than hyperhydric shoots. This study concludes that the hyperhydricity percentage of in vitro P. khinjuk shoots was reduced (12.8%) on modified MS medium with NH₄NO₃, CaCl₂·2H₂O and mT according to standard MS medium.