Effect of end-of-day far-red light from a movable LED fixture on squash rootstock hypocotyl elongation

Effects of end-of-day far-red (EOD-FR) light on hypocotyl elongation of a commercial cucurbit rootstock were investigated using movable and stationary light fixtures, since adequate hypocotyl length is required in vegetable grafting. Seedlings of an interspecific squash 'Tetsukabuto' (Cucurbita maxima x Cucurbita moschata) were grown in greenhouse and subject to daily EOD-FR light treatments with various application methods. The response of seedling hypocotyl length was well described using a Michaelis-Menten-type saturation curve over the range of 0-8.8mmolm ^-2d ^-1 FR light doses, as we previously reported for tomato rootstocks. Using a near saturating dose of 4.0mmolm ^-2d ^-1 FR light, efficacy of a movable FR light fixture for EOD-FR light treatment was compared with that of a stationary FR light fixture. The movable light fixture was a 120-cm metal bar equipped with FR light emitting diodes (LEDs) and the application was tested at two different traveling speeds (0.78 and 3.13mms ^-1) with one and four repeated applications per day, respectively, to reach the same target FR light dose (4.0mmolm ^-2d ^-1). Regardless of traveling speed, the extent of hypocotyl elongation under the moving FR LED fixture was statistically the same as that under stationary LED fixture and was 55-69% greater than non-treated control, suggesting that EOD-FR light applications can be designed flexibly. As far as we are aware, this is the first paper demonstrating the effect of EOD light quality treatment using moving light fixtures.