Growth and cropping of primocane and biennial raspberry cultivars grown under a film absorbing far-red light

In an attempt to control vegetative growth in raspberry (Rubus idaeus L.) in protected cultivation, we studied the effect of a far-red (FR)-absorbing greenhouse film on growth, cropping, and fruit quality in four raspberry cultivars. The primocane cultivars 'Autumn Bliss' and 'Polka' were grown in tunnels covered either with a clear film or a FR-absorbing film until the end of their first-year-harvest season. The biennial cultivars 'Glen Ample' and 'Tulameen' were treated similarly during their period of primocane growth. The FR-absorbing film increased the numbers of flowers in the primocane cultivars, whereas the numbers of flowers were reduced in the biennial cultivars during forcing in the following year. The numbers of flowers per plant were 185 in 'Autumn Bliss' and 171 in 'Polka' under the clear film; but 202 and 203, respectively, under the FR-absorbing film. The number of berries per plant was also increased in 'Polka'. The FR-absorbing film reduced cane growth in 'Polka', due to a reduced number of internodes, and in 'Tulameen', due to reduced internode length. The modified light spectrum had no effect on the berry contents of total anthocyanins, sugars, most mineral components, or on fruit colour in the primocane cultivars. However, levels of ellagic acid were increased by the FR-absorbing film, while the soluble solids content:titratable acidity ratio was slightly reduced. FR-absorbing films may therefore be useful when growing primocane raspberry cultivars in order to increase their yield potential, the contents of bioactive compounds in their fruit, and to decrease vegetative growth. However, such films may not be recommended for growing primocanes of biennial-type raspberry cultivars due to impaired flower development.