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

Abstract

SummaryThe flush leaves of seedling cocoa plants were assessed at each stage of the flush cycle from leaf unfolding to maturity for differences in leaf lamina presentation angle, surface hairs, stomatal number and development and leaf cuticle thickness. Changes in these parameters were then correlated with cuticular and stomatal diffusive resistance of the leaves. It is suggested that perpendicular positioning of the young flush leaves, the presence of surface hairs, the rapid synthesis of the cuticle and the limited stomatal development during the early stages of leaf expansion, restrict water loss from the developing leaves. Maximum rate of water loss from the leaves of a new flush was only attained after leaves were fully expanded, stomata fully developed and the leaves horizontally positioned. It is suggested that the large increase in water loss from the flush leaves following these changes might lead to an internal water deficit in the plant and hence to increased synthesis of abscisic acid in the shoot which, in turn, will maintain dormancy of the shoot apex in at least part of the interflush period.