Growth and flowering were studied in six black currant cultivars grown under natural photoperiodic conditions at angstrom s, Norway (59 degrees 40'N) at constant temperatures of 9 degrees C, 15 degrees C, or 21 degrees C during an entire growing season (May to late-September). Growth cessation and floral initiation were advanced and promoted by increasing temperature in the cultivars 'Ojebyn', 'Ben Tron', 'Kristin', 'Ben Hope', and 'Narve Viking', while early cessation of growth was advanced by low temperatures in 'Murmanschanka', a cultivar originating from the Kola Peninsula. In all cultivars, flowering was significantly increased by warm temperatures during the preceding growing season. A decline in growth preceded floral initiation by 2 3 weeks, indicating critical photoperiods of approx. 17 h and 16 h at 21 degrees C for the two processes, respectively, for all cultivars except 'Murmanschanka', which initiated floral primordia shortly after mid-Summer. Warm summer temperatures also affected flowering indirectly by the promotion of growth and advancement of the transition from the juvenile stage. Although the cessation of growth was normally associated with floral initiation, small plants with less than 20 nodes ceased growing under natural short-day conditions, but were unable to undergo floral initiation. It is concluded that summer temperatures influence flowering both directly, by enhancing short-day floral induction, and indirectly, by the enhancement of growth and, thereby, advancement of the transition from the juvenile stage.
