These initiate flowers in long-days at summer temperatures and so can produce fruit in the autumn of their first season. In the experiments reported here, the performance of 'Autumn Bliss', 'Autumn Treasure', 'Erika', 'Marcela', 'Polka' and 'Sugana' was compared.
After propagation, the plants were transferred on 19 May to heated greenhouses under natural long-day conditions in central Norway. The heating set-points were 15, 20 and 25 degsC, but the actual average temperatures achieved were 20.1, 21.7 and 26 degsC.
After five weeks, plants were transplanted to 7.5-litre pots and moved to a plastic tunnel. Fruit yield was positively related to the initial greenhouse temperature for all cultivars except 'Autumn Treasure'. The highest yields were obtained from 'Autumn Bliss' and 'Polka', although the highest temperature reduced the weight per berry.
The fruit of 'Polka' had an attractive glossy appearance and was of very high quality. However, the fruit was relatively dark coloured and some markets may prefer the fruit of 'Erika', which was also of high quality but redder in colour.
Earliness and Fruit Yield and Quality of Annual-Fruiting Red Raspberry (Rubus Idaeus L.): Effects of Temperature and Genotype by Sonsteby and Heide (2010). Journal of Horticultural Science & Biotechnology 85 (4): 341-349. The authors' abstract of their manuscript can be seen in full at www.jhortscib.com
Dr Ken Cockshull is emeritus fellow at Warwick HRI