THE EFFECT OF TIME OF GIRDLING ON CARBOHYDRATE CONTENTS AND FRUITING IN PONKAN MANDARIN (CITRUS-RETICULATA BLANCO)

Seasonal changes of sucrose, glucose and fructose were monitored in th e bark (phloem) and xylem in Ponkan mandarin (Citrus reticulata Bianco cv. Yoshida). Sucrose was the most abundant sugar. A decline in bark sucrose content coincided with the major fruit abscission period. Stem girdling was carried out at anthesis (May), end of June drop (July), start of autumn (September) and in early winter (November). Girdling i n July and September slightly increased leaf sugar content. At peak st arch content (in winter), the September girdled treatment had the high est starch content. May girdling increased fruit set significantly and also improved fruit color. July and September girdling improved fruit size, but late girdling (November) had no effect on fruit size. Flowe ring and fruit set in the following year were closely related to starc h content in the previous winter: they were highest in September girdl ed trees and lowest in May girdled trees. (C) 1998 Elsevier Science B. V.