Quantitative long-day flowering response in the perpetual-flowering F1 strawberry cultivar Elan

Abstract

SummaryPerpetual-flowering strawberry cultivars are commonly classified as photoperiodically day-neutral, even though early investigations demonstrated long-day (LD) regulation. An important reason for this inconsistency is that these freely flowering plants are difficult to establish in a true vegetative state, and experiments have therefore often been started using runner plants with pre-formed inflorescences. In order to circumvent this problem, we have used the perpetual-flowering F1-hybrid ‘Elan’ that is propagated by seed, and is thus not pre-conditioned by its earlier life history. The results demonstrated a marked quantitative LD response across a range of temperatures from 9° – 27°C. Seedlings were responsive to the LD stimulus at an early stage, and early flowering required LD exposure almost from germination. The critical daylength for the early flowering response was about 15 h at 18°C. Because of this threshold LD response, it is concluded that regulation of flowering is truly photoperiodic in nature, and not merely an effect of additional light. Flower development was also slightly advanced by LD conditions. Stolon formation was strongly enhanced by short-day conditions in combination with high temperature. Thus, not only flowering, but also runnering, was oppositely affected by photoperiod in ‘Elan’ compared with mono-flowering cultivars. The results are discussed in relation to the photoperiodic classification of strawberries.