Investigation of the Effect of Tree Trunk Girdling Time on Severity of Splitting and Quantitative and Qualitative Characteristics of Two Pomegranate Fruit Cultivars

 Major problems of pomegranate production, which is common in almost all of the world's pomegranate growing areas, especially in warm and dry regions, is the splitting of fruit, which is the most damaging to gardeners after pomegranate fruit moth. On the other hand, different studies indicate that girdling affects the quantitative and qualitative characteristics of different fruit trees. In the gird, the trunk skin must be completely removed so that the upper to lower skin relationship is completely cut off. The raw material that is absorbed by the root and rising through the xylem is transformed into a sap in the leaf, and in the return path through the phloem, it hits the barrier and accumulated above the wound site. Due to this process, sugar and plant hormones and starch reach the upper part of the wound girdling in trees for various purposes, such as raising the percentage of fruition of the plant, increasing size and increasing the quality and accelerating the fruition is done.

 An experiment was conducted to investigate the effect of girdling time on quantitative and qualitative properties of two red peel sweet and tart varieties in the Mahdi Shahr city, Semnan province. The girdling was taken at three full bloom days, two months after full bloom and four months after full bloom. To do a girdling, a double-edged knife was plunged into the trunk, and the ring-like cutting was done around the trunk. So that the layer of bark was cut from the trunk with a diameter of less than 2 to 3 mm continuously and separated from the trunk completely, so that the relationship between the top and the bottom was cut off. To evaluate qualitative and quantitative traits, 3 fruits were selected from the northern, southern and middle parts of each tree and transferred to the laboratory for measuring morphological and physiological traits. Physiochemical traits including pH, titratable acidity content, total soluble solids and morphological traits including weight, volume, average weight of 100 aryls and percentage of fruit juice, Ariel seed weight percentage, and split percentage were investigated.

 The results indicated that girdling at full bloom and two months after full bloom significantly reduced the percentage of fruit blooming in both cultivars compared to the control (non-girdling) treatment. Also, among the studied cultivars, percentage of splitting in red peel was higher than that of sour-sweet. In addition, girdling at full bloom and four months after bloom was able to increase weight, volume, and average weight of 100 aryls. Among two studied cultivars, sour-sweet showed higher soluble solids content and titratable acid percentage than red peel. It can be stated that photosynthetic materials in the crown of the tree are blocked by conducting a loop on the branch of the plant and prevent the transfer of these materials to the root. This allows the carbohydrates from photosynthesis to be transferred to fruits that are growing. As a result, the fruit grows more and subsequently increases its weight, volume, and number of aryls. In addition, the growth of root is reduced as a result of girdling and water, mineral salts, as well as growth regulators to the canopy and terminal meristem of the plant are slowed down, thereby significantly decreasing vegetative growth to be seen in the tree. Subsequently, with decreasing vegetative growth in the tree, the carbohydrate which is produced in the leaves is allocated to the growing fruits. This also increases the weight and volume of fruit in the tree. Since the girdling treatments are associated with meiosis (in full blooming stage) and in the stage of the growing of fruits cells (4 months after full bloom), it can be justified to enhancement of the weight and reduction of splitting percentage in the fruits of trees which is girdled. The main reason for this difference is the tension entered into the girdled trees at the interval between the application of the treatment and the wound healing.

 According to the results of this study, it was found that the process of girdling results in weight and volume enhancement of the fruit. In addition, the quantitative and qualitative traits investigated in the experiment were different in the two cultivars of red peel sweet and sour-sweet. In addition, girdling was effective on the pomegranate splitting, which is one of the important issues in the plantation of this fruit. However, the timing of the girdling at the full bloom and the four months after full blooming had the greatest effect on reduction of the severity of this complication.