Photoperiod extension effect on nursery tray-plants of everbearing strawberry

Photoperiod affects everbearing strawberry (Fragaria × ananassa Duch.) flowering and consequently the architectural structure of the plant: flowers, inflorescence, crowns and their position. Plant architecture represents an essential requirement to obtain programmed plants suitable for planned production. A photoperiod extension experiment was carried out in a high altitude (985 m a.s.l.) north Italian tray-plant nursery as an attempt to overcome the environmental limits, which are the main cause of low flower load. Runner tips of the strawberry 'Capri' were rooted in tray-pots in two tunnels in July 2012. From August to September, one of the two tunnels was exposed to a 24-h photoperiod extension. From November, the tray-plants were cold stored at -1.5°C before they were transplanted in April 2013. Until September 2012, no significant differences were observed on vegetative growth pattern. During spring 2013, the photoperiod treatment determined a significant increase in the total flower number plant-1 (30.5 vs. 14.3), caused by a higher number of trusses per plant (4.4 vs. 2.2) especially related to secondary inflorescences (2.2 vs. 0.5). Furthermore, the BBCH (Biologische Bundesanstalt, Bundessortenamt und CHemische Industrie) phenological growth stages showed that the extended photoperiod treatment reached a significant more advanced stage (median value: 'Seeds clearly visible on receptacle tissue' (BBCH 73) vs. 'First flowers open' (BBCH 60)). These results were confirmed by the maturation curves. The experiment proved the effectiveness of the technique. The light influence, derived from the extended photoperiod, clearly affected the flower induction, initiation and differentiation processes. The more advanced phenological stage suggests an advance and/or an acceleration of these processes, allowing the production of more secondary inflorescences