Effects of Ringing and Temperature on Flower Bud Differentiation of Satsuma Mandarin

Abstract

The effects of ringing with or without hand defoliation on vegetative growth, flower bud differentiation, and physiological changes in young, container-grown satsuma mandarin (cv.Okitsu Wase) on trifoliate orange were investigated. Comparisons were made between trees grown under different temperatures in a growth chamber and those grown in the field. A ring of bark, 3 mm wide was removed 5 cm above the bud union. The wound was wrapped with a vinyl tape to prevent drying and to enhance callus development.
1. Ringing in mid-June, after the spring growth flush ceased root growth within several days. After the ringing wound healed, new roots developed but the onset of the summer flush was delayed and shoot growth was depressed. Ringing in early September, after the summer flush stopped, not only depressed root growth, but it also prevented the initiation of new roots even though the girdles callused over. The absence of new roots is attributed to the lower air temperature in autumn. The autumn flush of new growth did not occur on treated trees.
2. Potted trees were ringed in either mid-June, late July, or mid-September. Ringed and non-ringed trees were defoliated, and then transferred to a 25°C growth chamber at intervals of 1.5 months. Number of flowers and vegetative shoots which emerged after defoliation was observed. Defoliation in mid-June of non-ringed control trees required new growth over 10 days. When trees were defoliated in late July, bud break occurred within several days.However, trees required more days again in mid-September, and the maximum of 20 days in late October for bud break after defoliation. Trees ringed in mid-June and defoliated in late July, mid-September, or late October required 15, 9, and 17 days, respectively, to initiate regrowth. Ringed trees in July or September caused regrowth similar to that of non-ringed trees. Trees defoliated in early December, girdled in July or September, and held at 25°C produced many flowers, whereas those ringed in June produced few flowers.
3. Trees, ringed on 1 September, and non-ringed trees were held at 15°, 20°, and 25°C in growth chambers or planted in the open field. The girdle produced more callus and healed faster at 25°C than at 20°C; no callus formed at 15°C. When trees at 25°C were defoliated in early December and kept at the same temperatures, bud break was delayed compared to those which were transferred to lower temperatures. Non-ringed trees held at 25°C produced few flowers, whereas ringed trees bloomed profusely. With or without girdles, trees kept at 15° and 20°C produced many flower buds; girdled trees kept at all temperatures had more flowers per sprouting node than did non-girdled ones.
4. Analysis of leaves from non-girdled trees growing in the field and from those girdled on 1 September revealed that the sugar content in all samples increased in autumn. The in-crease is attributed to the low air temperatures. After ringing, leaf starch content increased to over 20% (dry weight basis) and then decreased. Nitrogen content decreased linearly until the wound callused over and then the level increased. The C/N ratio increased until the wound healed and then decreased. Transpiration resistance of the leaves was temporarily greater on ringed trees; the upward movement of the transpiration stream was, therefore, slower until the girdle healed.