Morphology and anatomy of stems and pedicels of spring flush shoots associated with citrus fruit set

Abstract

Flowering and vegetative shoots of 'Shamouti' orange [Citrus sinensis (L.) Osbeck] and 'Marsh' seedless grapefruit (Citrus paradisi Macf.) were examined for correlation of their morphology and anatomy with fruit set. Fruit set is favoured on leafy inflorescences whereas abortion is nearly complete on leafless inflorescences. Leafless inflorescences of 'Shamouti' with one flower were found to have a very thin stem which contained few vascular bundles, whereas those with three flowers had better-developed vascular systems. The vascular system of leafy inflorescences is significantly different from that of leafless ones and contains a distinct central xylem cylinder. The vascular area of leafless inflorescences is only about one-quarter of that of the leafy ones. The vascular system of grapefruit resembles that of the 'Shamouti' orange. This study emphasizes the importance of the dimension of the vascular system for fruit set and provides a possible explanation for the better fruit set on both leafy and leafless inflorescences with several flowers compared with single-flowered inflorescences.