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Nodal cuttings (primary nodal explants) were used to initiate microcutting cultures of Hevea brasiliensis and Theobroma cacao. The physiological stage of growth reached by the branches from which the explants were taken had a considerable influence on culture initiation and response. In both species, the buds of the nodal explants taken from dormant brances (stages 11, 12 and 13 in Theobroma

stage D in Hevea) revealed greater opening ability in vitro and shoot elongation than buds taken from branches in a phase of active meristem growth in Theobroma (stages F1 and F2) or during a foliar growth phase in Hevea (stage C). In Hevea, the branch growth phase effect persisted into the multiplication phase when shoots developed in vitro were used as the source of secondary nodal explants. However, it disappeared during subcultures of primary nodal explants. In both species, the position of the nodes on the branch with respect to the apex also had an effect on culture initiation. The buds of nodes furthest from the apex were more likely to develop into shoots. In Hevea, the position of secondary nodal explants obtained from the primary shoot was seen to vary in effect depending on growth regulator applications during primary culture. These results are analyzed in terms of variations in the balance between endogenous growth promoters/inhibitors in the buds, depending on morphogenic stages and the bud position on the branch.

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