Phytohormones are chemical messengers involved in a wide spectrum of physiological and biochemical processes of higher plants at very low concentrations. Conventionally, phytohormones are classified into five classes: auxins, abscisic acid, cytokinins, gibberellins, and ethylene, as well as their precursors and synthesized analogues. In the 19th century, Charles Darwin first suggested that certain chemical compounds are capable of stimulating crop growth. Since then, a great deal of work has been done to study the stimulating impact of phytohormones on the quantity and quality of crops and vegetables.
Gibberellins (gibberellic acid (GA)) were discovered in studies carried out on the ascomycete fungusGibberella fujikuroi in rice plants, which were later isolated and named gibberellins А and В and subsequently detected in extracts of the marine algae genusFocus L. Most gibberellins are acidic and are indicated as GA (gibberellic acid) followed by a number corresponding to the order in which the gibberellin was discovered. GA1, GA3, GA4, GA5, GA6 and GA7 are the most active forms, and the rest are their precursors. Furthermore, the number of gibberellins in plants can be up to 136 types, while only a minority of them are biologically active.
SUMP EFFECT AND CALIBER IN CHERRIES
Good-sized, firm, attractive cherries with no splits, long, hydrated pedicels are desirable conditions for consumers and therefore preferred by growers.
The recent increase in cherry production around the world has placed new importance on the quality of the fruit and maintaining quality throughout the supply chain. However, with the adoption of early rootstocks that control size, there is a tendency for the fruit/leaf ratio of the tree to be excessive, leading to high yields of poor quality fruit (Whiting and Lang 2004; Whiting et al. 2005). ). An alternative approach to thinning to improve source-sink balance and fruit quality is to manipulate source-sink activity with exogenous plant growth regulators.
In this sense, gibberellic acid (GA3) is used to increase the hardness and size of the fruit, both in self-fertile and cross-pollinated varieties.
The exogenous application of phytohormones can be useful to return metabolic activities to their normal levels. At a certain concentration, GA3 has been shown to be beneficial for the physiology and metabolism of many plants subjected to e.g. abiotic stress, as it may provide a mechanism to regulate the metabolic process as a function of antioxidant and signaling enzymes. sugar.
Variables are the responses in the quality of the fruit and the characteristics obtained with GA3 applications. Cherries treated with GA3, will be firmer, larger, and heavier, compared to the controls, various studies demonstrate the above (Basak et al., 1998; Choi et al., 2002; Clayton et al., 2006; Facteau, 1984, 1986; Facteau et al., 1985a, 1985b; Horvitz et al., 2003; Kappel and MacDonald, 2002; Kupferman, 1989; Sive and Resnizky, 1988).
Fruit growth depends on the accumulation of dry matter and water and is determined, and may be limited, by its source-sink capacity and the availability of metabolites in the plant. The sink capacity of the fruit is considered the dominant factor in the competition for photoassimilates and is initially determined by the quality of the flower and the number of flowers formed on the tree (Guardiola., 1997).
It is necessary to additionally point out that some of the responses of cherries to exogenous applications of GA3 could probably also respond to environmental factors such as temperature, precipitation, humidity, water condition, nutrition and light (Facteau et al., 1985) or to the use of different varieties (Usenik et al., 2005). Timing of application and dosage may also be important.
EXPERIENCES IN CHILE
Various works carried out by Avium SpA have shown the great incidence of the use of GA3 as a complement to the nutritional program in cherry trees, on the most influential factors in their productive potential, such as Soluble Solids, Dry Matter and Hardness (Durofel), where each of these parameters have been directly and positively influenced by exogenous applications of GA3. (Tapia, C. 2015).
In the same way and as shown in tables 1 and 2, regarding the size and weight of the fruit, as well as the caliber distribution, the effect of complementary applications of GA3, have shown to obtain a clear positive impact on the mentioned parameters (Tapia , C. 2015), highlighting larger sizes and weight of the fruit on average, as well as a clear displacement of the caliber curve towards the calibers of greater commercial attractiveness.
The treatments (15, 30 and 45 ppm) were carried out on the Lapins variety, with cultural management of an orchard for export fruit and normalizing all the treatments according to their specific load. The application of AG3 in all the treatments was carried out in the state of straw color/beginning of veraison using a coverage according to 100% of the crown volume of the treated orchard.
Table 1. Effects of GA3 application on the diameter and weight of the fruit, cv. Lapins (Tapia, C. 2015)
Table 2. Effects of GA3 application on the size of the fruit, cv. Lapins (Tapia, C. 2015)
In the responses of fruit weight and diameter (table 1), all the treatments have differences with the control without application, regardless of the concentration of use in each one.
However, when analyzing the distribution of sizes (Table 2), there are significant differences for each treatment when each category of size is analyzed according to the equatorial diameter range of the fruit, but in turn there is a direct relationship to the concentration of use, taking higher proportion of fruit over Jumbo size (> 26 mm) as the concentration of use in ppm increases.
In conclusion, exogenous applications of GA3-type Gibberellic Acid, after the straw-yellow break stage (stage III/beginning of veraison), increases the size and hardness of the fruit, optimizing the source-sink activity of the fruit. Finally, in relation to the concentrations to be used, as already mentioned, these will depend to a great extent on environmental factors such as temperature, precipitation, humidity, hydric and nutritional condition, and light (Facteau et al., 1985) as well as the use of different varieties (Usenik et al., 2005).