Effects of chilling and night-break treatment on greenhouse production of 'Elsanta'

'Elsanta' strawberry plants were overwintered from 10 December until 23 January in several greenhouses under natural daylength conditions. The plants were divided into 8 groups. One received no chilling, the other groups received respectively 311, 343, 494, 571, 669, 719 and 749 hours chilling below 6 degrees C. After the chilling treatment plants were placed in a heated greenhouse and divided into 4 subgroups each of which was subjected to a night break treatment for 25, 35, 45 and 55 days, an additional group served as a control. The natural dark period was interrupted by low level incandescent lighting (10 W m(-2)) for 15 minutes every hour from 23.00 am until 7.00 pm. In the absence of chilling and night-break lighting plants remained very compact and produced short weak flower trusses with smaller and more misshapen fruits. Both chilling and night-break lighting could increase vegetative vigour, petiole and infloresence length, yield, fruit weight and fruit set. Insufficient winter chilling (0-343 hours) could be substituted in part by night interruption and was maximized by 45-55 days treatment. With chilling greater than 494 hours additive exposure to night-break lighting longer than 35 days did not further increase elongation of petioles and inflorescences. With plants receiving 571 hours of chilling followed by a night interruption treatment of 35 days yield and fruit set were maximized. With accumulated chilling length of petioles and flower trusses, fruit set, fruit weight and subsequent yield were not further increased.