Sensitivity of shoots and roots of young watermelon plants to end-of-day red and far-red light

The sensitivity of shoots and roots to end-of-day (EOD) red (R) or far-red (FR) light on growth of 'Sugar Baby' watermelon [Citrullus lanatus (Thunb.) Matsum amd Nakai] was investigated. Plants were grown in full-strength Hoagland solution and treated for 14 days to 15 minutes EOD light in trial 1 and in half-strength Hoagland solution and treated for 10 days to EOD light in trial 2. Exposing shoots to EOD FR resulted in elongated petioles of leaves 1 to 3 (as counted from the cotyledons), internodes 1 to 3, and total stem length in both trials. Exposure to EOD FR resulted in increased stem and petiole dry mass in trial 1, whereas EOD FR resulted in increased root and leaf dry mass in trial 2. EOD FR exposure of roots increased the length of petiole 4 in trial 1. In general, shoots were more responsive than roots to the growth-regulating effects of EOD FR.