Anatomy and transpiration of the avocado inflorescence

Abstract

Structure and function of the inflorescence of cv. ‘Hass’ and ‘Fuerte’ avocado (Persea americana Mill.) were examined by scanning electron microscopy (SEM) and by porometry. Sepals and petals could not be distinguished by their position in the flower, by visual gross morphology or by microscopic surface structure and were hence designated as tepals. These tepals were arranged in two whorls of three, followed by two whorls of three outer and three inner stamens, each opposite a tepal. The most conspicuous feature of tepals, developing leaves and peduncles was the dense cover of hairs which were most frequent on the adaxia] tepal surface (925-1200 trichomes mm'2), followed by their abaxial surface (625-1000 mm-2) and peduncles (375-655 mm-2). Stomata were absent from the adaxial surfaces of both tepals and leaves, as well as peduncles. On the tepals, abaxial stomata appeared functional, small (8-9 x 11-13 /¿m) and scarce with 2-8-34 stomata mm-2, i.e. very low relative to avocado leaves (350-510 stomata mm-3) or young fruit (50-75 stomata mm-3). However, flowers including tepals transpired 1-2-1 3 mmol under field conditions in Southern California (1-6-2 kPa), i.e. in excess of leaves (0-7-1-1 mmol) and peduncles (06-0-8 mmolHX) m-3 s-1). This situation was attributed to the few small but functional abaxial stomata on the tepal, in contrast to 80% closed stomata and dense epicuticular wax cover in form of rodlets on young and dendritic crystals on old leaves including the guard cells, and absence of stomata from the peduncle. © 1993 Annals of Botany Company.