Hormonal Changes Associated with Growth and Development of Red Raspberries

Analysis for gibberellin-like substances (GA) and cytokinins in cold and non-cold treated fall-bearing and cold treated June-bearing cultivars of red raspberries (Rubus idaeus L.) was made at the 10 and 20 node stages of growth (at 10 nodes, all plants were vegetative; at 20 nodes, only cold treated plants of fall-bearing cultivars were flower induced). Quantitative changes in GAs, as analyzed by the lettuce hypocotyl bioassay, were observed only in flower induced plants. In fall-bearing cultivars at the 20 node stage of growth, there was a 100% greater activity in cold than non-cold treated plants. Likewise, cold treated plants had a 60% greater activity at the 20 than at the 10 node stage of growth. Major qualitative differences in GAs were observed between the 10 and 20 node stage of growth in cold treated fall-bearing cultivars but not in cold treated plants of June-bearing cultivars. Changes in compounds at R_f 0.3 and 0.5 accounted for 35 to 54% of the total increase in GA activity between flower induced and non-induced stages of growth. Cytokinin activity tested by the tobacco callus bioassay was greater at the 20 than at the 10 node stage of growth in all cultivars and treatments. However, cold treated plants of the fall-bearing type had 70% greater cytokinin activity than non-cold treated plants at both stages of growth. It is suggested that gibberellins, possibly acting synergistically with cytokinins, are involved inflower induction in red raspberries.