Brown rot caused by Monilinia fmcticola is one of most serious postharvest diseases infecting red-flesh dragon fruits. Once infected, the quality of fruits is drastically reduced and the fruits are unlikely to be acceptable within a few days after infection. With the possible mechanism of Ca in controlling the growth of the fungus by reducing the activity of pectolytic enzymes of the causing organism and strengthening the host cell wall, the fruits were treated with four concentration of CaCl2 (0, 1.0, 2.0, 3.0 and 4.0 g L-1) at postharvest stage for 30 min, then inoculated with spore suspensions of M. fmcticola (106 spores ml-1). Results showed that the severity of brown rot was reduced with increasing CaCl2 concentration and this was supported by a strong negative correlation between fruit peel, Ca and disease severity (r=-95). Overall, the beneficial effects of elevated CaCl2 on quality parameters i.e., soluble solids, acidity and firmness were more apparent on severely infected fruits.

Fruits harvested at different maturity possess different biochemical constituents and physiological properties that make the fruits may react somewhat differently to the postharvest treatment. A study to examine the activity of Polygalacturonase (PG) and Pectin Methylesterase (PME) enzymes during storage in dragon fruit (Hylocereus polyrhizus) harvested at 28 days (Index 3) and 34 days (Index 5) after anthesis and postharvest treated with 0, 2.5, 5.0 and 7.5 g L-1 CaCl2 was performed. The PG activity was lower in younger fruit and vice-versa for PME activity. Increasing concentration of CaCl2 effectively reduced the activity of both enzymes. PG activity for fruit treated with 0, 5 and 7.5 g L-1 CaCl2 increased linearly with the time of storage while its activity for the fruit treated with 2.5 g L-1 CaCl2 was lower at the beginning of storage. PG activity of Index 5 fruits increased almost linearly during storage while its activity in Index 3 fruits was low at the early days of storage and later continued to increase until day seven. At both maturity indices, the PME activity was low at the early days of storage and later continued to increase until day seven. Overall, results obtained indicated that CaCl2 postharvest treatment reduced both PME and PG activities thus slowing down the softening process giving an evident that calcium possess a distinguishable role in the reducing softening of fruit, regardless of maturity index. � 2013 Science Publication.