Effects of Foliar Application of Gibberellic Acid, Copper Sulphate and Potassium Sulphate on Quantitative and Qualitative Characteristics of Pomegranate Fruit

Introduction
Pomegranate (Punica granatum) belongs to the Lytraceae family and is one of the most important fruit trees in Iran. Although pomegranate is considered as a low expectation fruit species and is relatively tolerant to various unfavorable conditions such as hot and dry climate, salty soil, and water deficit, however, commercial production of this fruit crop is faced with various challenges including different physiological disorders and biotic/abiotic stresses that can negatively affect pomegranate fruit yield, quality, and commercial acceptance. Fruit skin sunburn and fruit cracking are among the main physiological disorders that cause serious economic losses to the pomegranate growers all around the world and may account for losses of up to 40-50 % of the total fruit production in different pomegranate production areas.
Materials and methods
To reduce physiological diosorder of fruit cracking in pomegranate cultivar cv. Malase-Saveh, gibberellic acid, potassium sulfate and copper sulfate treatments were utilized as a factorial design in the frame of randomized complete block design with three replications. Gibberellic acid (0 and 100 ppm), potassium sulfate (0 and 5000 ppm) and copper sulfate (0 and 2500 ppm) were sprayed in three stages of fruit development in the late spring and mid-summer. The fruit samples were harvested randomly from different sides of the pomegranate trees at the ripening stage of fruit and some characteristics of fruit were measured.
Results and discussion
Results of analysis of variance has illustrated that most of the evaluated parameters were significantly affected by foliar treatments. The number of fruit cracking was counted for each tree and results showed that fruit cracking was influenced by the application of gibberellic acid, potassium sulfate and copper sulfate, as the percentage of fruit cracking was reduced significantly with application of these compounds. The fruit weight, peel thickness, moisture percentage of peal, TSS and titratable acidity was significantly increased by 100 ppm GA3 compared to the control sample. The highest fruit weight (181.7 gr) was obtained in 100 mg gibberellic acid treatment, while this parameter was 160.75 gr in the control plant. The lowest level of fruit cracking was related to gibberellic acid treatments with levels of 100 mg/l with mean values of 14.10%. The highest amount of fruit cracking was observed in control plant (23.38%). Finally, fruit cracking percentage was reduced by the rise of peel thickness, moisture percentage of peel, and titratable acidity in fruit.
Conclusions
In this study, the effects of gibberellic acid, copper sulfate and potassium sulfate were investigated on the fruit cracking of pomegranate fruit. The overall results showed that the application of gibberellic acid and copper sulfate significantly affected some of the attributes of pomegranate fruit and finally led to the reduced fruit cracking in ‘Malase-Saveh’ cultivar. The results obtained from this research indicate that the fruit cracking of pomegranate is related to many physicochemical characteristics of the fruit and tree. The results of this investigation can enhance our knowledge about the major contributing factors on pomegranate fruit cracking, and will be benefcial for making sound horticultural practices to reduce the detrimental effects of pomegranate physiological diorders.