Enhancement of Floral Initiation and Bud Development by Chilling of Root Cuttings in Primocane-fruiting Blackberries

Abstract

In previous studies we found that primocane-fruiting blackberries (PFB) form flower buds soon after the plants start suckering from root cuttings collected in winter or early spring. Research was carried out to test if the same phenomenon holds true in summer-collected plant material. Root cuttings of A-1836, APF-13 and NC194 PFB were dug from the field on 31 July 1997 and stored in plastic bags at 2 °C for 32 days. On 1 Sept., freshly dug root cuttings along with the cold-treated ones were stuck in 3.8-L plastic pots, which were kept in a lath house for 4 weeks and then moved to a greenhouse under natural daylength. Significant differences occurred for plant emergence between chilled and non-chilled plants (16 days vs. 31 days, respectively). Transition from vegetative to floral phase was first observed in cold-treated A-1836 and APF-13 at five-node growth stage, with floral structures clearly evident in both selections at seven nodes of growth 45 days after planting. Chilled APF-13 and A-1836 started to bloom on 26 Nov. and 5 Dec., respectively. The first fruit of APF-13 were picked on 10 Jan. 1998. By this date, cold-treated NC194 and all non-cold-treated plants remained stunted with rosetted leaves, showing no signs of floral initiation. These findings present evidence that low-temperature exposure prior to shoot emergence greatly promotes flowering and fruiting in PFB. The results might have applicability in blackberry culture under greenhouse conditions.