MORPHOLOGY AND ANATOMY OF STEMS AND PEDICELS OF SPRING FLUSH SHOOTS ASSOCIATED WITH CITRUS-FRUIT SET

Flowering and vegetative shoots of 'Shamouti' orange [Citrus sinensis (L.) Osbeck] and 'Marsh' seedless grapefruit (Citrus paradisi Macf.) w ere examined for correlation of their morphology and anatomy with frui t 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 whi ch contained few vascular bundles, whereas those with three flowers ha d better-developed vascular systems. The vascular system of leafy infl orescences is significantly different from that of leafless ones and c ontains a distinct central xylem cylinder. The vascular area of leafle ss inflorescences is only about one-quarter of that of the leafy ones. The vascular system of grapefruit resembles that of the 'Shamouti' or ange. This study emphasizes the importance of the dimension of the vas cular system for fruit set and provides a possible explanation for the better fruit set on both leafy and leafless inflorescences with sever al flowers compared with single-flowered inflorescences. (C) 1996 Anna ls of Botany Company