Effects of temperature around the fruit on sugar accumulation in watermelon (Citrullus lanatus (Thunb.) Matsum. & Nakai) during the latter half of fruit developmental period

Abstract

Nursery plants of watermelon (Citrullus lanatus (Thunb.) Matsum. & Nakai) were planted in the field on April 19, 2006. To examine the correlation between temperatures around fruit during the latter half of the fruit developmental period and sugar accumulation in fruit, fruits were covered with polyethylene (PE) film, infrared- ray-blocking (IRB) film, and black nylon mesh (BNM) from 20 to 48 days after anthesis (DAA). Relative to the untreated control, higher fruit temperatures were detected by PE film-covering, but the temperatures remained low by IRB and/or BNM film-covering. Fruit growth was significantly accelerated by PE film-covering, but IRB and BNM film-covering resulted in a reduction of fruit growth. Cell enlargement at the intermediate and outer regions of fruit progressively intensified in the former as compared with the latter. Higher fructose and sucrose contents were detected in the intermediate and outer regions of fruit by IRB film-covering, while PE film-covering decreased glucose and fructose contents in all regions of fruit. These results suggest that the active cell enlargement caused by higher temperature during the latter half of the fruit developmental period is closely correlated with the reduction of sugar content in fruit, and that higher sugar content can be produced by lowering temperature with IRB film-covering in this period. JSHS © 2009.