Nutrient-hormone interactions in citrus: Physiological implications

Abstract

Citrus growth and development is regulated by complex but subtly tuned nutritional and hormonal interaction in response to environmental signalling. Flower induction is stimulated by low temperatures and water stress and mediated by previous fruit load, being endogenous gibberellins (GAs) content pointed as the main inhibiting hormones. The promoting role of carbohydrates or nitrogen (N) on flowering has not been demonstrated, but a minimum content of these compounds seems to be required for flower formation. Fruit set is a critical step for fruit production, being initially regulated by GAs content. Thereafter, during the onset of the source-sink competition, fruit set depends upon carbohydrates and N availability and fruitlets sink strength. During stage II of fruit development, fruit growth is promoted by auxins, carbohydrates and water accumulation. Afterwards, peel colour development, which is stimulated by low temperatures, is promoted by the decline of flavedo's GAs content and the steady-state level of ethylene, as carbohydrates and abscisic acid (ABA) increase and N decrease during this final stage.