Effect of Foliar Application of Paclobutrazol on Freezing Tolerance of Almond (Prunus dulcis cv. Ferragnes) Plants

Protecting young seedlings from frost damage is an important issue for newly established orchards and nurseries. Paclobutrazol (PBZ) is a plant growth inhibitor that can alleviate some damage caused by environmental stresses. In this study, the effect of PBZ on cold tolerance of almond (Prunus dulicis) saplings of cultivar 'Ferragnes' was investigated. The research was conducted in a randomized complete block design, and treatment consisted of five concentrations of 0 (control), 125, 250, 500 and 1000 mg/l of Cultar (containing 250 grams per liter of PBZ) sprayed on one-year-old almond saplings in September. Stem and bud samples were collected on November 11, March 10, and January 10; and January 15 and March 15, respectively. Stem and bud samples were subjected to low temperatures (0, -5, -10, -15, -20, and -25 degrees Celsius), then exothermic point and electrolyte leakage were evaluated. Application of PBZ, especially at concentration of 500 mg/l, increased free proline, soluble carbohydrates and dry matter, but decreased relative water content and electrolyte leakage. In January, the first exothermic point was on average 4 °C lower in the samples treated with 500 mg/l PBZ than in the control. Considering LT50 temperatures, saplings treated with 500 mg/l PBZ showed 5 °C higher winter hardiness than control plants. The results indicate that PBZ effectively reduces winter frost-induced damage to almond saplings.