Effect of Foliar Application of Potassium Nitrate, Calcium Nitrate, and Boric Acid on Reduction of Pre-harvest Fruit Splitting of Page Mandarin

Pre-harvest citrus fruit splitting is a physiological disorder that causes significant damage to producers of susceptible cultivars by reducing the amount of crop available on the market. Proper management of tree nutrition and paying special attention to the three key elements of potassium, calcium, and boron, which are involved in the strength of cell walls and fruit peel flexibility, can be effective in reducing the fruit splitting severity. Therefore, an experiment has been carried out in the Ramsar (Citrus and Subtropical Fruits Research Center) during 2018 and 2019 to investigate the effects of foliar application of 1.0% potassium nitrate, 1.0% calcium nitrate, and 0.5% boric acid at the end of June drop on reducing the severity of splitting and some fruit traits of Page mandarin. This study is performed according to a combined analysis in time with two factors including years of experimentation and different treatments of foliar application of nutrients, based on randomized complete block design with three replications. The results show that the treatments especially 1.0% potassium nitrate have reduced pre-harvest fruit splitting, increased the yield, and improved the quantitative and qualitative fruit traits. However, they have had no significant effect on the activity of polygalacturonase enzyme, cell density of blossom-end, and navel diameter. Overall, foliar application of nutrients, especially 1.0% potassium nitrate, could be suggested as an effective approach to control pre-harvest fruit splitting and boost the quantity and quality of page mandarin fruit.