Soil Calcium Application and Pre-Harvest Calcium and Boron Sprays on Mangosteen Fruit Quality Attributes

Mangosteen (Garcinia mangostana L.) is susceptible to translucent flesh disorder (TFD) and gamboge disorder (GD). Both are apparent only on the fruit's flesh making external visual inspection impossible. The influence of soil calcium (Ca) application and pre-harvest Ca and boron (B) sprays on these disorders was investigated in an experimental plot in Chantaburi, Eastern Thailand. The soil was Typic Paleudults with sandy clay loam texture. Five treatments were applied to the mangosteen to investigate the relationship between nutrient concentration and incidence of TFD and GD. These treatments are 1) no treatment (control), 2) soil Ca only, 3) soil Ca and Ca spray, 4) soil Ca and Ca + B spray, and 5) soil Ca and B spray. Soil Ca was applied once as gypsum at 4 kg/tree in September 2004. The Ca spray was applied six times in 2005 and three times in 2007 using 2% CaCl2 center dot 7H(2)O. The B spray was applied three times each in 2005 and 2007 using 0.25% solubor. The fruit samples were harvested in the middle of May of 2005 and 2007. At harvest, the fruits were separated into three groups based on their size: small (<60 g), medium (60-90 g) and large (>90 g). Then, they were classified as normal fruits, TFD fruits, or GD fruits. The concentrations of K, Ca, and B in the flesh, rind and peduncle were analyzed. It was found that the soil Ca application - with or without foliar sprays - significantly reduced the number of TFD. However, the Ca concentration in the flesh did not differ significantly between normal fruits and TFD fruits. Instead, we found that the ratio of K/Ca in the flesh is a good indicator of TFD. The study revealed that high K/Ca ratio led to more TFD in mangosteen. In general, flesh Ca decreased with fruit size while flesh K increased. As a result, larger fruits tend to have more TFD than smaller ones. When soil Ca was applied, the number of GD was significantly lower than the control. The soil Ca treatment became even more effective when combined with B spray or Ca + B spray, particularly the latter. However, treatment of soil Ca together with Ca spray did not reduce GD considerably. Furthermore, it was found that the nutrient concentrations in all parts of GD fruits were not measurably different from normal or TFD fruit. However, it was clear that Ca + B spray along with soil Ca treatment effectively reduced the number of GD. On the other hand, an excessive amount of Ca treatment without the complement of B did not lower the amount of GD fruit. We recommend that soil Ca together with pre-harvest spray of Ca + B is useful for reducing the number of TFD and GD fruits.