The Potential of Zinc and Boron Fertilization to Reduce Longan Peel Reddening Disorder

Abstract

Since potassium chlorate (KClO₃) has been found to reliably induce longan flowering, Thai farmers are able to sustain longan production all year round. However, the continuous use of KClO₃ is affecting longan trees by causing disorders during certain phonological stages. Among those is the longan peel reddening disorder (PRD). When affected by PRD the skin of the fruit turns red and hard, preventing it from growing. Meanwhile, in Northern Thailand PRD has a considerable economic impact on longan farming and method for remediation are sought. The aim of this study was to identify ways of combatting PRD through improving the micro nutritional status of the longan trees. Therefore, boron (B) and Zinc (Zn) were applied by foliar sprays and the effect on longan fruit growth was compared to non-treated trees. The experiment was organized following a completely randomized design (CRD) with 7 treatments and 5 replications. The treatments were as follows; 1) control (no micronutrient spray), 2) 0.1% B, 3) 0.2% B, 4) 0.1 Zn, 5) 0.2% Zn, 6) 0.1% B + 0.1% Zn, 7) 0.2% B + 0.2% Zn.  As a result, in the first month, the control had a higher significantly fruit set per bunch as compared to the foliar application of Zn and B. Analyzing fruit quality at harvest, was found that the foliar application of Zn and B resulted in a significantly higher flesh and fruit weight per bunch as compared to the control and the treatments with only one micro-nutrient applied. With respect to width and length of fruit, total soluble solids, peel weight and seed weight no significant differences were found. However, the skin color differed significantly among the treatments: After zinc and boron 0.2 concentration foliar application fruits developed from light green into bright yellow at the harvesting stage. Leaves treated with Zn and B foliar sprays showed higher concentrations of both micro-nutrients as compared to non-treated. This showed that the Zn and B foliar application can be absorbed by the leaves and accumulated in the plant tissue in order to ensure the sufficient supply in every growth stage. While the experimental set-up was not appropriate to prove that PRD was the effect of micro-nutrient deficiency, it was shown that the foliar application of Zn and B can reduce the occurrence of PRD in longan. In order to ensure sufficient supply of Zn and B foliar spray applications can be recommended.