Techniques for manipulation of the annual growth cycle in raspberry

I n the accompanying paper we described how the growth cycles of biennial and primocane fruiting raspberry cultivars are controlled by the environment, the genotype and cultural practices (Carew et al., 2000). For plants to fruit outside their normal season, these growth cycles need to be manipulated and optimized for fruit production at speci®c times of the year. Techniques to achieve this are discussed in this paper and areas are identi®ed which are less well understood and in need of further investigation. Raspberries can be produced under protection to exploit the high prices of an early or late season, fresh market crop; during week 21 in 1998 prices were as much as four times greater than during the main cropping season (week 26 onwards) (Figure 1). Despite this, it is estimated that in 1997, of the 1280 ha of raspberries grown in the UK, just 3% were protected (Janet Allen, ADAS, pers. comm.). A number of factors currently limit protected raspberry production. For example, for biennial cultivars poor and uneven bud break can result not only in a reduction in yield, but also in an irregular picking season (Jennings, 1988). In the autumn, when the prices are again high, primocane fruiting cultivars could be used to extend the season. However, this potential is often not realised because cropping is terminated by frosts. These and other associated problems with out-of-season raspberry production need to be addressed to guarantee productivity and pro®tability and to allow UK growers to compete with imports.