The feasibility of bridge-grafting to restore the flow of sucrose in girdled Ocotea bullata and Curtisia dentata medicinal trees

Abstract

Ocotea bullata (Burch.) Baill. (Lauraceae) and Curtisia dentata (Burm.f.) C.A.Sm. (Curtisiaceae) are two South African indigenous medicinal tree species of which the bark is overexploited due to its high demand in the local medicinal plant trade. The bark of O. bullata is used for headaches, as an emetic for both nervous and urinary disorders, and for diarrhea, whereas the bark of C. dentata is taken for stomach ailments, diarrhea and sexually transmitted diseases. Curtisia dentata bark is further applied as an aphrodisiac, and to “purify the blood”. Due to uncontrolled harvesting of bark by informal commercial harvesters, these trees are often found girdled in natural areas. The removal of bark from a tree affects its foliage, flowering, fruiting, seeding, basal sprouting and rooting since the removal of phloem tissue during girdling affects both the basipetal flow of carbohydrates from the canopy of the tree to the root system and the acropetal flow of amino acids, sugars and hormones from the roots to the canopy. This study investigated whether the flow of sucrose can be restored in girdled O. bullata and C. dentata trees using the technique of bridge-grafting. A total of 300 bark samples were collected bi-monthly over a 12-month period to perform targeted 1H NMR based metabolomic analyses to determine the sucrose concentration of each sample. Fluctuations in sucrose concentrations occurred at every sampling date, however, sucrose dynamics in the bridge-grafted trees appeared to be restored after one year.