Growth Response of Seedlings of Flame Azalea to Manual and Chemical Pinching

Abstract

Abstract Seedlings of flame azalea [Rhododendron calendulaceum (Michx.) Torr] were subjected to the following manual pinching treatments at the 10-,12-,14-,or 16-leaf stage: no pinching, removal of the terminal two nodes [approximately 1.25 cm (0.5 in)] and removal of terminal growth[approximately 2.5-5.0 cm (1-2 in)] leaving six nodes. The greatest number of lateral shoots (5.3) was produced by removing the terminal two nodes at the 16-leaf stage. Generally, the number of lateral shoots increased with the leaf stage at which manual pinching was imposed. Removal of terminal growth, leaving six nodes, resulted in the lowest leaf, stem and root dry weights at each leaf stage. In a second experiment, dikegulac [Atrimmec;sodium salt of 2,3:4,6-bis-0-(l-methylethylidene)-α-L-xylo-2-hexulofuranosonic acid], at 0, 2000, 4000, 6000 or 8000 ppm, was applied to both nonpinched and manually-pinched plants (removal of the terminal two nodes at the 16-leaf stage). Dikegulac (Atrimmec) treatment significantly affected the nurnber of lateral shoots and dry weights of leaves, stems and roots. The number of lateral shoots increased linearly with concentration up to 4000 ppm. At 6000 and 8000 ppm, the average number of shoots produced (9.4 and 9.6, respectively) was similar to 4000 ppm. Both pinched and nonpinched plants treated with dikegulac (Atrimmec) produced more lateral shoots than manual pinching alone. Dry weights of leaves, stems and roots decreased as the concentration increased. However, the number of lateral shoots and dry weights of leaves, stems and roots of pinched and nonpinched plants were not significantly different when treated with dikegulac (Atrimmec)