Growth and Development of Blackberry Cultivars

Abstract

Environmental control of growth and flowering is generally well understood in raspberries, but a complete understanding of the processes is missing in blackberries. To get a better understanding of growth and flowering in blackberries, five cultivars, ‘Loch Ness’, ‘Loch Tay’, ‘Natchez’, ‘Ouachita’, and ‘Sweet Royalla’, were studied in the phytotron at 16°C and 12, 13, 14 and 15h photoperiod, and under natural temperature and daylength conditions at Apelsvoll, Norway (60.7° N). The results demonstrate that origin and genetic background of cultivars play a crucial role in how they respond to environmental signals. ‘Natchez’ had a critical photoperiod of 14h for cessation of growth at 16°C, while ‘Loch Ness’ continued to grow independently of photoperiod treatment. Photoperiod in the 12-15h range was not critical for flower bud initiation in ‘Natchez’ and ‘Loch Ness’. All five cultivars initiated flower buds before cessation of growth under out-door conditions. In both experiments, the cultivars that reached growth cessation first, also had the most advanced flower buds, except for ‘Ouachita’. Flower bud initiation in ‘Loch Ness’ and ‘Natchez’ began in the mid-section of the cane and continued in both basipetal and acropetal directions. Three ‘Loch Ness’ plants from each photoperiod treatment were forced in the greenhouse after sufficient chilling to examine the flowering performance of the buds that were initiated before growth cessation. Plants at 15h photoperiod, had the highest percentage of flowering nodes, most flowers per plant and fewest days to anthesis at forcing, but all plants from all treatments developed flowers. The position of the flowering nodes along the cane corresponded to the position of the initiated flower buds dissected in ‘Loch Ness’ prior to chilling. The results suggest that temperature, rather than photoperiod, may be the main factor affecting both growth cessation and flower bud initiation in blackberries.