Relationships between total leaf area and fruit weight in vertically and horizontally trained watermelon [Citrullus lanatus (Thunb.) Matsum. et Nakai] plants

Relationships between total leaf area per plant and fruit weight were investigated in vertically and horizontally trained watermelon [Citrullus lanatus (Thunb.) Matsum. et Nakai] plants. Watermelon plants grafted on bottle gourd (Lagenaria siceraria Standl.) were grown in a glasshouse. In the vertically trained system, elongating shoots were initially suspended with polyethylene strings and then draped over horizontally stretched steel wire about 180 cm above the bed. In the horizontally trained system, shoots were spread on the ground. Each plant had one hand-pollinated fruit. In the vertically trained system, fruit was suspended in a cross-tied polyethylene string. In Experiment 1, June-harvest culture, 'Honey-syaruman', 'Yoshino' and 'Wase-tenryu' seedlings were planted at a density of 95.2 plants (.) a(-1) (95.2-190.5 shoots (.) a(-1) with a LAI <1). In Experiment 2, November-harvest culture, one group of 'Wase-tenryu' seedlings was planted at densities of 95.2 and 190.5 plants (.) a(-1) (190.5 to 285.2 shoots (.) a(-1) with LAI of 1.69 to 2.13) and trained vertically. A second group of seedlings was planted at a density of 31.7 plants (.) a(-1) (63.5 shoots (.) a(-1) with a LAI <1) and trained horizontally. 1. In both June-harvest and November- harvest cultures, fruit weight was closely related to total leaf area per plant in the vertical or horizontal trainings. 2. Fruit weight in the vertically trained plants was significantly lighter than that in the horizontally trained ones even when the total leaf area was similar. 3. The training method or the total leaf area per plant had little or no influence on the total soluble solids contents of the fruit. 4. These results indicate that fruit weight of watermelon is basically determined by total leaf area per plant although some other factors (e.g. light interception characteristics) may be also involved.