Solving yellow sap contamination problem in mangosteen ( Garcinia mangostana ) with Ca²⁺ application based on fruit growth stage

摘要

Yellow sap contamination causes poor quality of mangosteen fruits. Yellow sap is an issue when the sap contaminates the surface of the fruit or aryl. It is caused by the break of yellow sap duct in fruit rind. The break of yellow sap duct is connected with low concentration of Ca²⁺ in the fruit pericarp. Source of calcium and stage of fruit development affect uptake and translocation of Ca²⁺ to the fruit pericarp. This study aims to determine: (1) the best time for Ca application, (2) the frequently of Ca application, and (3) the effects of the presence of xylem and casparian strips on Ca²⁺ translocation in mangosteen plants. The study was conducted in Lampung (Sumatra) and Bogor (West Java), Indonesia between January 2011 to April 2013. Ca source is calcite (CaCO₃) at 17 kg calcite per tree for the experiments conducted in Lampung and 10 kg Calcite per tree in Bogor. The results showed that the blooming time was the best period for Ca application in both study location. The critical time of Ca uptake was between the first and the fourth weeks after blooming. Application of Ca twice could reduce yellow sap contamination on aril and pericarp. In Bogor, Ca²⁺ application at 4.5 kg year^-1 tree^-1 at anthesis stage reduced the percentage of yellow sap contaminated fruit on the aryl to 33% and 30% respectively. In Lampung, twice application of Ca at anthesis and 4 weeks after anthesis (WAA) reduced the percentage of yellow sap contaminated fruit on the aryl to 10% compared to 50% of that of control.