Influence of photoperiod and duration of short-day treatment on vegetative growth and flowering of strawberry (Fragaria x ananassa Duch.)

In Junebearing strawberry cultivars, flowering is induced by short photoperiod, which also reduces vegetative growth. The loss in vigour can lower yield if plants are not cold treated to restore vegetative growth. The aim of this study was to find a photoperiod treatment that induces flowering but does not reduce vegetative growth in strawberry 'Korona'. Plants were subjected to different photoperiods (12, 13.5 or 15 h) for varying durations (21, 35 or 49 d). After treatments, effects on plant development were recorded during forcing at 18 h daylength. Floral induction was comparably successful in 12 and 13.5 h photoperiods and the number of flowers and yield were increased by lengthening the treatment. Induction failed in many plants treated in a 15 h photoperiod and flowering was poor regardless of duration of treatment. Shorter photoperiod increased the number of branch crowns and reduced runner production, and these effects were enhanced by lengthening the treatment duration. Reduction in vegetative growth measured by petiole length was most obvious in 12 h photoperiod in ail treatment durations, although the differences between treatments rapidly disappeared during forcing. Twelve and 13.5 h photoperiods were equally efficient in producing yield, but more vigorous vegetative growth was maintained during treatment in a 13.5 h photoperiod.