BIOCHEMICAL AND PHYSIOLOGICAL ASPECTS OF LEAF DEVELOPMENT IN COCOA (THEOBROMA CACAO)

Abstract

SummaryThe dormant phase of the flush cycle of leaf growth in cocoa is known to be correlated with high abscisic acid (ABA) levels in the mature leaves of the new flush (NF) and previous flush (PF) leaves. Defoliation of either the NF leaves or PF leaves of cocoa seedlings reduced the length of the dormant phase of the flush cycle, thus showing that the mature leaves were a source of growth inhibitors which could affect shoot apical activity. The application of ABA to the NF and PF leaves led to an extension of the dormant phase, whereas application of zeatin or gibberellic acid decreased it. The distribution of [14C]ABA following its application to NF and PF leaves at different stages throughout the growth cycle showed that [14C] ABA was accumulated by the bud in relatively larger amounts during the final stages of bud dormancy (I‐1 and I‐2) than in the earlier stage (F‐2). The results suggest that internal competition for nutrients may be responsible for the inhibition of growth at the F‐2 stage but that ABA translocated from the mature leaves causes the buds to remain dormant during the subsequent stages of I‐1 and I‐2.