Mirjana Sadojevic
Engineer
Abstract
The chilling requirements of ‘Junifer’, ‘Rovada’ and ‘Red Dutch’ red currants and ‘Mucurines’ and ‘Pax’ gooseberries were studied under controlled environment conditions. Field grown single-stem potted plants were chilled at 0°C from October 15 for 0 to 20 weeks and forced in a lighted greenhouse at 20°C and 18 h photoperiod for 60 days for recording of budbreak and flowering. None of the red currant plants were able to break without chilling, while the number of breaking buds increased linearly with more than four weeks of chilling, and fastest so in ‘Junifer’. ‘Red Dutch’ proved to have a particularly deep and stable dormancy. Comparable but markedly lower chilling requirements were found in the two gooseberry cultivars. While more than 20 weeks of chilling were required for full dormancy release in the red currant cultivars, 16 to 20 weeks were adequate for the ‘Mucurines’ and ‘Pax’ gooseberries, respectively. This compares with a chilling need of 14 weeks at 0°C previously found for most commercial black currant cultivars under the same conditions. The results also confirm that, as previously demonstrated for black currants, flower development requires more chilling than bud break itself also in red currants and gooseberries. This highlights the need for extended chilling of the plants before the plants are set to forcing in modern tunnel production. We also conclude that the red currant cultivar ‘Rovada’ with its large berry trusses seems particularly well suited for tunnel production.
Abstract
We studied the environmental control of shoot growth and floral initiation in annual shoot plants of four red currant cultivars under phytotron conditions. Under natural day length conditions at Ås, Norway (69°40’N), the cultivars ‘Junifer’, ‘Red Dutch’, and ‘Rosetta’ ceased growing and initiated irregular flower formation at 24 and 18°C in late August, indicating a critical photoperiod of approximately 15 h. At 12°C and under outdoor conditions, the processes were delayed by 3-6 weeks depending on the cultivar, indicating a critical photoperiod of approximately 14 h under Nordic field conditions. In 10-h short day (SD), the cultivars ‘Junifer’, ‘Red Dutch’ and ‘Rovada’ ceased growing within 2-3 weeks at 18 and 24°C and within 2-4 weeks at 12°C, followed by irregular floral initiation. However, in 20-h long day (LD), flower initiation was generally scarce, and with contrasting temperature responses among the cultivars, flower initiation was advanced by low temperature in ‘Red Dutch’ and by high temperature in ‘Rovada’ and ‘Junifer’. Flowering performance in the following spring confirmed these results, which demonstrate that red currants are quantitative SD plants with diverse temperature and photoperiod interactions.
Authors
Mirjana SadojevicAbstract
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.