Physiological fall of citrus fruits

In citrus crops, the evolution from flower to fruit depends on several factors: varietal or genetic, environmental (temperature, humidity, wind, rain, etc.) and physiological (nutrition, metabolism, hormonal balance, health status of the crop, etc.). The genetics of the variety and the environmental conditions cannot be altered in growing conditions, since in one way or another they occur naturally.

Citrus fruits, like many other fruit trees, produce many flowers, although different falls of flowers and fruits are identified over time:

  • – fall prior to anthesis,
  • – fall of flowers during and/or after the anthesis, which determines the initial setting, and
  • physiological fall of fruits (Agustí et al. 1982) or fall of June in the northern hemisphere, until the beginning of the linear growth phase of the fruit, which determines the percentage of fruit set and, therefore, the potential of the final harvest.

The falls of developing fruits are produced by the separation of the peduncle in those who have not fertilized well and / or those who are not able to maintain a high rate of development unlike others who are able to continue absorbing nutrients. Subsequently, and throughout the period of its development, falls continue to occur, in much smaller quantities, separating by the chalice area.

Today, there are several studies in which it is shown that in the processes that determine the fall of fruits are involved the phytohormones promoters and inhibitors of growth.

  • – Growth promoters are auxins, gibberellins, polyamides and cytokinins.
  • – Growth inhibitors are abscisic acid (ABA) and ethylene.

In citrus fruits, the most important role is played by gibberellins (Talón et al., 1992), whose presence stimulates the transport of mineral and photoassimilated elements to the ovary.

Auxins are related to the process of cell elongation during fruit growth and, therefore, to its final size (El-Otmani et al., 1995; 2000).

Cytokinins also participate in the process of cell division and in the reactivation of ovarian growth after anthesis, making it possible to set. Its action is similar to those of gibberellins, increasing the sinking capacity of the ovary and increasing the transport of mineral elements and carbohydrates to it (El Otmani et al., 1990; Werner et al., 2008).

Abscisic acid (ABA) acts as a potent developmental inhibitor and abscission activator. Under normal conditions, both during the fall of petals and in the transition from the phase of cell division to that of cell elongation, the concentration of ABA increases in those ovaries with reduced growth rate, whose abscission is significantly increased (Zacarías et al., 1995).

The competition for the carbohydrates (sugars) available in the plant, is also one of the factors that determine the percentage of fruits in the plant to be the main cause of the fall of fruits in development.

The magnitude of abscission depends on the competition between the developing organs, being greater the greater the number of flowers and fruits and / or the lower the availability of carbohydrates to nourish their development. Competition is established from the beginning of flower development (Agustí et al., 1982).

 

 

Therefore, competition for nutrients during ovarian development is one of the limiting factors of curdling. The fruit is the most important sinking organ and claims a large amount of the carbohydrates available in the tree during its development, limiting as it grows the vegetative development (Mehouachi et al., 1995; Martínez-Alcántara et al., 2015). In this sense, the presence of leaves plays a determining role due to their ability to synthesize and export metabolites to the developing fruit.

That is why the fruits located in a better position, that is, in shoots with young leaves, have greater persistence in the tree than those located in shoots without young leaves, more prone to abscission due to the lower availability of carbohydrates within their reach during the initial development.

In summary, it can be said that there are two fundamental factors that regulate both the setting and the physiological fall of fruits: on the one hand, it significantly influences the hormonal balance of the plant (promoters and inhibitors) and on the other, competition for nutrients (sugars, polysaccharides, etc.). Stress conditions such as a deficit or excess of water in the soil should also be avoided, which can cause a decrease in the flow of nutrients, which would produce a greater fall of fruits.

In this sense, in AGROMETODOS we have AM·EN®, which is a very active organic product whose formulation combines micro and macroelements in a balanced way, among which are magnesium, manganese and zinc.

Its formulation acts on certain metabolic and physiological processes of high energy activity in plants. Applied at the right time, it induces cell division and elongation of meristematic and tissue cells, as well as other young tissues related to physiological fall, fattening and fruit quality.

The field efficacy of AM·EN® is comparable to the most widely used synthesis phytoregulators on the market. The application of AM·EN®:

  • – Regulates the physiological fall and the mooring of the fruits.
  • – Greater homogeneity of calibers.
  • – Greater number of fruits harvested without losing quality.
  • – Does not slow down vegetative development. It does not unbalance the plant.
  • – Does not produce phytotoxicity.

Likewise, the product is authorized for use in Organic Agriculture and registered as an input by FiBL (Forschungsinstitut für biologischen Landbau in German) and can be used by Demeter certified farmers.

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