Effect of EOD-FR Treatment on the Growth and Morphology of Japanese Mustard Spinach and Pak-choi

Abstract

The effect of irradiation with far-red (FR) light at the end of the day (EOD) on the yield and traits of 4 varieties of Japanese mustard spinach (Brassica rapa var. perviridis) and 3 cultivars of pak-choi (B. rapa var. chinensis) were investigated. When the ‘Maruba-komatsuna’ of Japanese mustard spinach was exposed to FR light under high irradiation (96.0 mW・m^–2) by EOD treatment, all investigated traits tended to increase more than in plants without treatment. On the other hand, for other varieties, ‘Hakkei’, ‘Nanasa’, and ‘Nanane’ receiving low irradiation (34.3 or 13.4 mW・m^–2) were compared with those receiving strong irradiation (96.0 or 56.7 mW・m^–2). Depending on cultivars, they are different reactions under low or high irradiation for Japanese mustard spinach. Also, in ‘Okinawa-Chingensai’ of pak-choi, stem elongation on receiving EOD-FR treatment was promoted by more than 2 times in comparison with no treatment, but this was not observed with ‘Mini-chingensai’ or ‘Choyo’. The results showed that EOD-FR treatment promoted the effect of stem elongation in some cultivars, but it had no effect on pak-choi.