Spring frost harm to blossoms has been a serious problem in pistachio harvesting lands of Iran. Using mineral nutrients has been offered as a measure to alleviate or prevent frost harm. The objective of the present study was to investigate the effects of potassium and zinc application on the spring frost damage of pistachio flowers. Treatments were three levels of K2SO4 (0, 1 and 2 %) and three levels of ZnSO4 (0, 0.5 and 1 %). The nutrition solutions were sprayed on trees at two times (bud swell stage and green tip stage) in 2017–2018. The excised 1-year old twigs were collected during full blooming stage. The shoot segments were exposed to three different freeze test temperatures (0, −2 and −4 °C) and some relevant physiological and biochemical changes were evaluated. Compared with control, the application of K2SO4 and ZnSO4 decreased freezing injury, electrolyte leakage percentage, hydrogen peroxide (H2O2) and malondialdehyde (MDA) concentrations of flowers after freezing tests. The most nutrient treatments especially 1% K2SO4+1% ZnSO4 increased significantly soluble proteins, soluble carbohydrates, total phenolic compounds, proline, guaiacol peroxidase and catalase enzyme activity of flowers. The results of the present study could have implications for improving the freezing tolerance of temperate fruit trees cultivated in cold regions by the use of potassium and zinc.
