Changes in Dormancy and Sensitivity to Vernalization in Axillary Buds of Satsuma Mandarin Examined in vitro During the Annual Cycle

Abstract

Effect of season and the presence of fruit on bud-endodormancy and the flowering response to low temperature treatments were determined using bud cultures of Owari satsuma mandarin ( Citrus unshiu Marc). Bud dormancy was deeper in fruiting as compared to defruited trees. In fruiting trees, the intensity of bud dormancy was highest in spring, decreased to a low value by early Jul. and then increased until early winter. This increase in dormancy during summer and early autumn did not occur in non-fruiting trees. No flowers formed in buds cultured between May and Sep. Both in fruiting and defruited trees, buds became competent to show a vernalization response to chilling by the end of Oct., at the time they also became capable of sprouting in vitro at low temperature (15/10 °C). There was a direct effect of fruit on the buds which persisted long after fruit removal and resulted in a reduction of the flowering response to chilling.