ENHANCING STRAWBERRY PRODUCTION AT HIGH LATITUDES

Finland is situated between 60 and 70° north latitude. Growing conditions are characterized by hard winters with variable snow cover, springs with frequent frosts at bloom, and short growing seasons with long-day conditions extending until end of summer. In these conditions, the occurrence of winter injury is the major factor limiting strawberry cultivation. Flower initiation begins in September, in several areas only one month before the end of the growing season. Strawberry production in Finland is primarily based on perennial cultivation of short-day cultivars in open field. The harvesting period is usually no more than one month. Strawberry production under protection is a minimally used method, although cultivation in polyethylene-covered tunnels advances the start of fruiting season to early June and extend it up to the end of September. Everbearing cultivars are not yet commercially cultivated. MTT Agrifood Research Finland has a strawberry breeding programme underway with an aim of broadening the supply of cultivars adapted to northern conditions. The main targets of the breeding programme are resistance to strawberry mildew and improved fruit firmness and climatic fitness. The ongoing breeding programme has introduced the cultivars ‘Kaunotar’, ‘Suvetar’, ‘Valotar’ and ‘Lumotar’. In order to develop an everbearing cultivar fit for northern conditions, seedling populations were created by hybridizing everbearing and short-day strawberries. The everbearing parents included cultivars of different origin of the perpetual flowering trait. Some crossing combinations produced offsprings of high percentage (up to 100%) of seedlings flowering in long-day conditions. To test the feasibility of everbearing cultivars for protected cultivation in Finland, several cultivars were tested in a production system set up in a polyethylene tunnel. In the trial, the best cropping cultivars produced 600 to 800 g/plant when spring propagated plants were used. In comparison, the crop of larger, winter-stored, two-year-old plants was twice that of spring-propagated plants. For the most productive cultivars, the seasonal yield totalled approximately 1,200 g/plant.