THE INFLUENCE OF FRUITING ON THE BUD SPROUTING AND FLOWER INDUCTION RESPONSES TO CHILLING IN CITRUS

The effect of chilling temperatures on bud sprouting and flower format ion was compared on fruiting and non-fruiting 'Owari' satsuma mandarin (Citrus unshiu Marc) trees. On non-fruiting trees, bud dormancy was w eak, and a significant proportion of buds were able to sprout at high temperatures without being chilled. Separate effects of low temperatur es on bud sprouting and flower induction were demonstrated. On fruitin g trees these two effects of low temperatures were also demonstrated o n summer-flush buds, but not an older (spring-flush) buds. The spring- flush buds from fruiting trees scarcely sprouted without being chilled . These buds required a longer chilling period for dormancy release th an for flower induction, and it was not possible to separate the effec t of low temperature on flower induction from the effect on dormancy r elease. The presence of fruit reduced flower formation by reducing bud sprouting. Furthermore, fruit had a direct inhibitive effect on verna lization which resulted in increased formation of vegetative shoots. T he effect of fruit and low temperature on flowering was unrelated to c arbohydrate accumulation in the leaves or the roots.