Effect of climatic factors, gibberellic acid, mineral ‎nutrients concentration on fruit splitting of ‎Washington Navel orange and pomegranate (Punica ‎granatum L.) in Egypt

A field experiment was conducted during the 2019–2020 and 2020–2021 seasons in private orchards of Washington Navel orange (C. sinensis) budded on sour orange (C. aurantium) rootstocks (20 years old) in Al-Dakahlia Governorate and Wonderful pomegranate (10 years old) in Al-Behera Governorate, Egypt. At the start of the study, the percentage of fruit splitting was assessed in four directions (north, east, west, and south) and at three canopy positions (upper, middle, and lower). Samples of Washington Navel orange and Wonderful pomegranate fruits, with and without splitting symptoms, were collected to determine calcium (Ca) and boron (B) content in the fruit peels. The experiment aimed to evaluate the effects of calcium chloride, boric acid and gibberellic acid on fruit splitting and fruit quality. Twenty-five trees of each fruit species were divided into five groups, and each group was sprayed three times at full bloom, 30 days and 60 days after full bloom with one of the following treatments: 150 ppm GA₃, 2.0% calcium chloride (CaCl₂·2H₂O), 0.3% boric acid (H₃BO₃) and 150 ppm GA₃ + 2.0% CaCl₂·2H₂O + 0.3% boric acid. The results revealed that the highest rates of fruit splitting occurred in July, coinciding with high temperatures, intense solar radiation, and low relative humidity. Fruit splitting was more prevalent on the southern side and the lower canopy portion. Higher concentrations of calcium and boron were detected in the peels of non-split fruits compared to split ones. The combined treatment of 150 ppm GA₃, 2.0% CaCl₂·2H₂O, and 0.3% boric acid was the most effective in reducing fruit splitting and enhancing yield and fruit quality of Washington Navel oranges and Wonderful pomegranates. Therefore, this treatment is recommended to reduce fruit splitting and improve yield and quality parameters of Washington Navel orange and Wonderful pomegranate under experiment conditions.