This study represents the first paper of the effects of growth regulators on the physiochemical and phytochemical properties of the wax apple fruit, a widely cultivated fruit tree in southeast Asia. Net photosynthesis, sucrose phosphate synthase (SPS) activity, peel color, fruit firmness, juice content, pH value, total soluble solids (TSSs), and the sugar acid ratio were all significantly increased in growth regulators (PGRs) treated fruits. The application of gibberellin (GA(3)), naphthalene acetic acid (NAA), and 2,4-dichlorophenoxy acetic acid (2,4-D) significantly reduced titratable acidity and increased total sugar and carbohydrate content compared to the control. The 50 mg/L GA₃, 10 mg/L NAA, and 5 mg/L 2,4-D treatments produced the greatest increases in phenol and flavonoid content; vitamin C content was also higher for these treatments. PGR treatment significantly affected chlorophyll, anthocyanin, and carotene content and produced higher phenylalanine ammonia lyase (PAL) and antioxidant activity levels. There was a positive correlation between peel color and TSS and antioxidant activity and both phenol and flavonoid content and PAL activity and anthocyanin formation. A taste panel assessment was also performed, and the highest scores were given to fruits that had been treated with GA₃ or auxin. The study showed that application of 50 mg/L GA₃, 10 mg/L NAA, and 5 mg/L 2,4-D once a week from bud development to fruit maturation increased the physiochemical and phytochemical properties of wax apple fruits.
The present study represents the first report of the effect of hydrogen peroxide (H(2)O(2)) on the growth, development and quality of the wax apple fruit, a widely cultivated fruit tree in South East Asia. The wax apple trees were spray treated with 0, 5, 20 and 50 mM H(2)O(2) under field conditions. Photosynthetic rates, stomatal conductance, transpiration, chlorophyll and dry matter content of the leaves and total soluble solids and total sugar content of the fruits of wax apple (Syzygium samarangense, var. jambu madu) were significantly increased after treatment with 5 mM H(2)O(2). The application of 20 mM H(2)O(2) significantly reduced bud drop and enhanced fruit growth, resulting in larger fruit size, increased fruit set, fruit number, fruit biomass and yield compared to the control. In addition, the endogenous level of H(2)O(2) in wax apple leaves increased significantly with H(2)O(2) treatments. With regard to fruit quality, 20 mM H(2)O(2) treatment increased the K(+), anthocyanin and carotene contents of the fruits by 65%, 67%, and 41%, respectively. In addition, higher flavonoid, phenol and soluble protein content, sucrose phosphate synthase (SPS), phenylalanine ammonia lyase (PAL) and antioxidant activities were recorded in the treated fruits. There was a positive correlation between peel colour (hue) and TSS, between net photosynthesis and SPS activity and between phenol and flavonoid content with antioxidant activity in H(2)O(2)-treated fruits. It is concluded that spraying with 5 and 20 mM H(2)O(2) once a week produced better fruit growth, maximising the yield and quality of wax apple fruits under field conditions.