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BREEDING RASPBERRIES FOR TOLERANCE TO ADVERSE CLIMATIC CONDITIONS
For example, the purple ‘Amethyst’ cultivar is intermediate between its red parent ‘Cuthbert’ and its black parent ‘Robertson’.
The cultivar ‘Robertson’ is a selection from the wild discovered in the Black Hills area of South Dakota and ‘Cuthbert’ is of New York origin (12). The observation that ‘Robertson’ was a shinier black raspberry than most other cultivars was the primary reason for its use as a parent since a shiny purple was the desired objective. ‘Amethyst’ has shown sufficient hardiness for Iowa conditions as noted from its performance in cultivar trials and observation notes taken during its period of testing and propagation(2). Thus, the evidence that purple raspberries generally are hardier than their black parents.
In general, most blacks and purples grown in Iowa utilize a competing cover crop as a means of hardening.
In the wild native black raspberries generally have conditions requiring either a higher tolerance of cold or sufficient competitive growth for increasing hardiness by increasing soluble solids in the cell sap.
Among the red raspberries, Latham has frequently been the hardiest cultivar; yet it, too, winterkills especially when there are fluctuating temperatures during the dormant season.
One of the most recent innovations in raspberry breeding is the production of summer bearing types which produce fruit on new wood.
They have also been termed everbearing raspberries because of this trait although the "summer fruiting" term seems more appropriate.
Because these cultivars produce berries on current season’s growth or primacanes, the fruit buds escape or evade the winterkill of regular summer fruiting cultivars. ‘Pathfinder’ and ‘Trailblazer’ (4) are typical of these types.
Earlier introductions of fall bearing types include ‘St.
Regis’, ‘Indian Summer’, ‘September’, ‘Durham’, and ‘Fallred’. ‘Heritage’ is one of the more popular recent cultivars (10) of the late summer or fall fruiting types.
It appears to be a successful means of escaping winter-kill of fruit buds.
Thus, breeding combined with innovative cultural practices of hardening and selection have resulted in more hardy raspberries for the mid-west and upper Great Plains areas (4). Further development of techniques and breeding practices are needed for hardier cultivars of red, black, and purple raspberries for the mid-west and high plains area of the U.S.A.