Extreme short-day induction requirements for flowering in the late-flowering strawberry cultivar ?Malwina?

We studied short-day induction of the strawberry (Fragaria x ananassa Duch.) cultivar ?Malwina? under both phytotron and field conditions. Flowering was assessed by crown dissection of treated plants and subsequent flowering performance. Serial dissections revealed no visible changes in crown apices during the first 4 weeks of short day (SD) at 18?C in the phytotron, while after 6 weeks, all plants had formed rudimentary flower primordia with visible sepals. At 9?C, the same stages were reached after 8 and 10 weeks of SD, respectively. When subsequently forced in long day (LD) at 20?C, no substantial flowering took place after less than 6-week SD treatment at 18?C, while full flowering required 10 weeks of SD induction. At 9?C, full flowering was not obtained even after 10 weeks of SD treatment. Under field conditions, the ?Malwina? plants did not reach floral development stage 2 before 22 October, approximately a month after ?Frida? and ?Sonata? which reached this stage on 21 September, and 3 weeks after ?Florence?. SD exposure resulted in repeated crown branching in ?Malwina? and we suggest that early spontaneous abortion of the emerging floral primordium takes place under unsaturated SD induction conditions, thus causing crown branching and hence, delayed floral initiation and development.