Influence of kaolin, calcium oxide, and boron trioxide sprays to reduce sunburn and enhance fruit productivity and quality in Murcott mandarin

Climate change has increasingly disrupted the growth and development of many fruit crops. Among the associated challenges, sunburn caused by excessive light and solar radiation is a major physiological disorder affecting citrus and other fruit species. This study evaluated the potential of kaolin (KL), calcium oxide (CaO), and boric acid (B2O3) to mitigate sunburn and improve fruit set, yield, and quality in Murcott mandarin. Foliar sprays were applied at concentrations of 2000, 3000, and 4000 ppm KL, either alone or in combination with CaO and B2O3 at 0 CaO + 0 B2O3, 500 ppm CaO + 50 ppm B2O3, and 1000 ppm CaO + 100 ppm B2O3. Applications were performed four times during each season (mid-March, early July, early August, and early September) in 2023 and 2024. The results demonstrated that foliar application of KL, CaO, and B2O3 significantly increased fruit set, yield, and both physical and chemical quality attributes by reducing sunburn incidence across both study seasons. The most effective treatments were 4000 ppm KL + 500 ppm CaO + 50 ppm B2O3 and 4000 ppm KL + 1000 ppm CaO + 100 ppm B2O3.