Nutrient-Hormone Interactions in Citrus: Physiological Implications

Abstract

Growth and development in woody perennial plants has many differences regarding to annual crops. After overcoming the juvenile stage, in which species are not able to produce fl owers, each annual cycle in perennials give rise to one or more fl ushes of vegetative and reproductive growth.Under tropical conditions, Citrus annually brings about several sprouting and blooms, whereas growing in temperate climates, only the spring fl ush is reproductive. In temperate zones, although several fl ushes of growth may occur, these are mostly vegetative. The exception is provided by lemon trees ( C . limon [L.] Burm.), which give rise to reproductive and vegetative shoots throughout the year.Vast information is available relating nutrition and water supply with fl owering and fruiting of Citrus . However, less information matching the controlling role of nutrients, carbohydrates, water and hormones during the developmental process is available. Therefore, hormonal and nutritional control of some Citrus developmental processes, with special emphasis on fl oral induction, fruit set, fruit development and maturation of Citrus has been focused in this chapter. AbstractCitrus 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 fl owering has not been demonstrated, but a minimum content of these compounds seems to be required for fl ower 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 fl avedo's GAs content and the steady-state level of ethylene, as carbohydrates and abscisic acid (ABA) increase and N decrease during this fi nal stage.

Effect of Potash Application on Yield and Quality of Kinnow Mandarin in Sandy Loam Soils of South Western Zone in Haryana, India

“…Potassium regulates the osmotic potential of plant cell and activates enzymes that are involved in respiration and photosynthesis [2]. When K is deficient in citrus trees, the rates of photosynthesis reduces and results in a negative effect of fruit set, yield and quality [4]. Potassium content does not usually affect tree growth over a wide range of variation, unless it falls below 0.4% [5].…”