Fruit splitting occurrence of Shogun mandarin (Citrus reticulata Blanco cv. Shogun) in southern Thailand and alleviation by calcium and boron sprays

Abstract

Fruit splitting is a serious problem of Shogun mandarin in southern Thailand. To alleviate this impact, the applications of calcium and boron by spraying were investigated. An experiment was established in a farmer orchard (at Amphur Sadao, Songkhla province) where four-year plants were grown at 6 m x 6 m spacing. The experiment was arranged as a completely randomized design, and 16 trees were used. There were 4 treatments (1. control or water spray, 2. 1% CaCl2 spray or C treatment, 3. 0.8% boric acid spray or B treatment and 4. 1% CaCl2+ 0.8% boric acid spray or C+B treatment) with 4 replicates. The application was started at 4 months after fruit-setting, the sprays were done at 1 month intervals. It was found that the occurrence of fruit-splitting started at 3 months after fruit-setting, and there were 4 causes of fruit-splitting: 1. scab (28.33%), 2. sun scald (11.11%), 3. sun burn (7.78%) and 4. no primary peel damage (52.78%). Various patterns of fruit splitting were found: vertical, horizontal, oblique and informal shape. The treatments of calcium and boron sprays did not affect on fruit growth or fruit size compared with the control, but they significantly enhanced fruit firmness, total soluble solid (TSS) and total acidity (TA). The treatments of C, B, and C + B can reduce the percentages of fruit splitting to 5.56, 8.89 and 6.67%, respectively, and they were significantly different from that of the control (52.22%). It is suggested that calcium and boron sprays can alleviate fruit splitting in Shogun mandarin, and fruit quality is also enhanced.

Keywords

• fruit splitting
• calcium
• boron
• Shogun mandarin