Long-Day Flowering Response of Everbearing Strawberries

Octoploid strawberry (Fragaria x ananassa Duch.) cultivars can be classified into mono-flowering (single-cropping or June-bearing) and perpetual-flowering (everbearing) types according to their horticultural performance. Whereas floral induction in mono-flowering cultivars is well-documented, the literature on the control of flowering of perpetual-flowering cultivars is rather inconsistent. Photoperiod and temperature control of flowering in several perpetual-flowering strawberry cultivars of widely varying pedigree were therefore studied in controlled environments. Flower bud initiation in all cultivars was significantly advanced by long day (LD) conditions at temperatures of 15 degrees C and 21 degrees C; while, at 27 degrees C, flowering took place under LD Conditions only. When vegetative plants growing in short day (SD) at 27 degrees C were transferred to LD conditions at the same temperature, they consistently initiated flower buds and started flowering after about 4 weeks. At such a high temperature, flowering could thus be turned on and off by switching between SD and LD conditions. At 9 degrees C, flowering was substantially delayed, and, at this temperature, flowering was unaffected by photoperiod. Runner formation was generally promoted by high temperature and SD conditions, but the photoperiodic effect varied between experiments. We conclude that everbearing strawberry cultivars, in general, whether of the older European type or the modern Californian type, are qualitative (obligatory) LD plants at high temperature (27 degrees C), and quantitative LD plants at intermediate temperatures. Only at temperatures below 10 degrees C these cultivars are day-neutral.