Effects of overnight illumination with green or yellow lights on flowering and growth in some strawberry cultivars

The effects of overnight illumination with a green light on flower bud emergence and growth in strawberry plants were investigated while comparing the effects of overnight illumination with yellow light, which is usually used as an illuminator for moth control. Five cultivars of strawberry runner plants whose terminal flower buds had been artificially induced were subjected to overnight illumination for 73 days using either green or yellow light of varying irradiance (0.02-0.10 micro mol/square m/s), and the subsequent flower bud emergence were observed. The results showed no delay in flower bud emergence under green light in comparison with the control (non-illuminated) up to 0.06 micro mol/square m/s for 'Akihime', 'Sagahonoka' and 'Benihoppe'. Under yellow light, on the other hand, there was no delay in flower bud emergence up to 0.06 micro mol/square m/s for 'Sagahonoka', and up to 0.04 or 0.02 micro mol/square m/s for 'Benihoppe' or 'Akihime' respectively. Although 'Sachinoka' showed no delay in the emergence of the primary axillary inflorescence under green light up to 0.04 micro mol/square m/s, the flower bud emergence was already delayed under yellow light at 0.02 micro mol/square m/s. 'Tochiotome' showed no delay in flower bud emergence under green or yellow light, but under yellow light, the number of leaves in axillary branches for 'Tochiotome' increased. In addition, in all cultivars under yellow light, there was a tendency for the petiole and leaf lengths to increase spindly, and for the leaf color to become paler with increasing irradiance. These results indicate that even at higher irradiance, green light has little effect on flower bud emergence and on leaf growth in comparison to yellow light. We conclude that the use of green light for moth control is highly beneficial to strawberries, which have photoperiodic responses and show high sensitivity to light, in comparison with that of yellow light.