Growth and Fruit Characteristics of Seedless Watermelon Plants under Different Light Intensity Levels

This study was conducted to investigate the effects of different light environments on the vegetative and reproductive growth of seedless watermelon (Citrullus lanatus Thunb.), particularly on female flower initiation and fruit characteristics.The experiment was carried out in an unheated multi-span greenhouse at the Watermelon Research Station, Jeollabuk-do Agricultural Research and Extension Services, using the small-fruited seedless cultivar 'Black Boy'.Five light treatments were applied: natural light (NL), 70% and 30% shading of NL, and supplemental lighting (SL) at 120 and 240 PPFD.Air temperature and light intensity inside and outside the greenhouse were automatically recorded every 30 minutes from the first pollination to the pre-harvest period.Plant growth parameters and female flower occurrence were monitored weekly.The number of female flowers was most stable under the natural light condition and significantly decreased under shaded conditions.In particular, the 70% shading treatment resulted in the lowest number of female flowers throughout the experiment, whereas under the 240 PPFD supplemental lighting treatment, more than 3.5 female flowers per plant were observed around 40 days after transplanting.Under the greenhouse conditions of this study, fruit enlargement was markedly reduced under shading compared with the control, while no significant differences were observed among the supplemental lighting treatments.These results suggest that basic light conditions strongly influence reproductive growth and female flower differentiation.Therefore, in the cultivation of small and medium sized seedless watermelon under low light conditions, supplemental lighting can be effective in improving fruit set rate and subsequent fruit enlargement.