Influence of Trunk Strangulation on Growth and Water Absorption by Young Pummelo Trees Exposed to High Temperature.

Abstract

Young 'Tosa Buntan' pummelo (Citrus grandis (L.) Osbeck) trees on trifoliate orange (Poncirus trifoliata Raf.) rootstock were sand-cultured in the pots and transferred to a growth chamber kept at 30°/25°C (day/night) from early November in 1991 to late May in 1992. The trunks of the potted trees were strangulated with wire at a tension of 30 or 40 Kgf. cm degree in mid-December, when shoot growth in the first flush had stopped. Shoot growth in the second flush was decreased by the strangulation treatments, but there was no significant difference between the two strangulation treatments. A part of the wire ring at 40 Kgf. cm degree was covered with bark callus after a 5-month treatment, but the ring at 30 Kgf. cm degree was not covered until early June. Water absorption and transpiration rates of the tree were decreased by the treatments as were the net photosynthesis rates of the leaves. Water absorption rate in the 40 Kgf. cm degree treatment was slower than that in the 30 Kgf. cm degree treatment until mid-February, but the rate of the former became faster than that of the latter thereafter. Flower buds sprouted not only on the previous year's shoots but also on the first flush shoots on strangulated trees ; but control trees failed to flower. The number of flower buds was not significantly different between the two strangulation treatments, but they abscised after flowering in late May. The shoots and leaves in the second flush weighed less on dry weight basis in the strangulation treatments than they did in the control. The dry weight of the small roots on strangulated trees was also lighter than it was in the control.