Some effects of light intensity, daylength and temperature on growth of fruiting and non fruiting watermelon (Citrullus lanatus)
1978
Buttrose, M.S. | Sedgley, M.
Plants of watermelon [Citrullus lanatus(Thunb.) Matsum. & Nakai, cv. Early Yates] were grown for up to 3 months after germination in controlled environment cabinets, and various aspects of vegetative growth and fruit development were measured. Effects of light intensity were studied by comparing growth at 8, 16 and 32 klx at constant temperature and daylength (25 °C, 14 h). Effects of daylength were studied by comparing 8, 14 and 24 h at constant light intensity and temperature (32 klx, 25 °C), and effects of tem perature were studied by comparing 20°, 25°, 30°, 35° and 40 °C at constant light intensity and day- length (32 klx, 14 h). With increasing light intensity and daylength lateral growth was promoted whereas main shoots were less affected. Increase in temperature above 25 °C resulted in longer main shoots and prolific lateral growth, due both to more and to longer laterals. Environmental differences had little effect on internode length but did affect the size of basal leaves. However, an increase in total leaf area at higher temperatures or with Continuous light was mainly due to more leaves rather than larger leaves. The presence of developing fruit greatly reduced vegetative growth of plants. Main shoot length, lateral growth, number of leaves, and even size of individual leaves, were all reduced. This reduction did not apply to d. wt of whole plants. Fruiting plants were very efficient, on a leaf area basis, in accumulating d. wt. At 25 °C at the two higher light intensities with 14 h days the presence of one developing fruit was inhibitory to the setting of any subsequent fruit. With short days or low light, more fruits were set but they were small. With continuous light or high temperature more than one fruit could develop and they were large.
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