By: Carlos J. Tapia T. Agricultural Engineer M. Sc. Specialist in cherry production. Technical Director Avium.
- When auxins are applied early, at the white bud stage, they can positively influence the retention of set fruit and the development process, reducing fruit drop and ensuring production.
- This is due to antagonism with abscisic acid (ABA), which is the phytohormone of senescence.
- On the other hand, according to local research, the use of gibberellins (AG) is supported3) as essential for gaining size in the final stage of fruit formation prior to harvest.
Auxins, cytokinins and gibberellins are the most important phytohormones that act as growth regulators in cherry trees. When choosing to use these regulators, it is essential to ensure the balance of the plants in terms of technical/cultural management to maintain an adequate level of reserves, optimal vegetative development, load regulation according to the orchard's potential and to maintain perfect water management according to the demands of the crop at each phenological stage.
Once the cherry harvest is over, it is a priority to focus on the nutritional recovery of the plant, its extraction of nutrients is a fundamental task to achieve maximum productive potential. Given the physiology of fruit formation in sweet cherry and considering the speed of its phenological advances from full flower to harvest, it is suggested to pay maximum attention to be successful.
“The development of cherry fruit is very fast, we even find varieties with a shorter cycle with 45 days from full blossom to harvest (DDPF). This path is known as the “perfect race”, where every oversight can reduce its maximum potential. Already in the season, nutritional programs, both foliar and soil, are a basis for being able to maximize the development of the fruit and foliage and thus achieve their maximum potential. These programs must be adjusted to the specific characteristics of each variety/rootstock combination, since in practice clear differences are recognized in the demand for different nutrients and some special needs.” said Carlos Tapia, director of Avium.
As a complementary aspect to nutritional programs, the use of plant growth regulators (PGR) is required. These are part of specific actions to enhance the formation of fruits in the different phases of their development. Their use must go hand in hand with an appropriate balance of the orchard in different areas (reserves, load regulation and water management).
The constant work of growth regulators such as auxins, cytokinins and gibberellins are managed during three different phenological stages of the plant, which are cell division, stone hardening and cell elongation.
Auxins.
The first stage of cherry tree formation, from flowering to the hardening of the stone, corresponds to cell division. This is the moment when the cells that make up the fruit are generated and their division is essential.
During this period, the use of auxins has a direct effect on the active growth of reproductive and vegetative organ tissues, and the synthesis in plants is carried out by the juvenile meristems of shoots, flowers and fruits. However, their action is secondary and never more important than cytokinins and gibberellins.
Various investigations have determined that in addition to what was mentioned above, the action of auxins has been related to the retention of fruit once the flowers have been fertilized by the antagonism with abscisic acid (ABA), which is the phytohormone of senescence.
“A synthetic auxin type such as 2,4 DP has shown that, in early applications in cherry trees, at the white bud stage, it can positively influence the retention of set fruit and the development process, reducing fruit drop at the end of the process and ensuring production. It should be noted that auxins do not have a direct effect by enhancing fruit set, but rather work as inhibitors of the abscission of already formed fruit and not as enhancers of fertilization and subsequent fruit set." Tapia added.
Cytokinins.
The phytohormones most closely linked to the cell division process are cytokinins, which, depending on the variety, could extend up to 25-30 days after full bloom (DDPF). Although there is scientific evidence that it could begin as early as the exposed bouquet prior to the white bud stage.
Over time, different sources of natural cytokinins have been used through foliar applications from full flower, especially using zeatins, beatins, among others, with positive effects on the increase in fruit size in stage I of cell division and which would be inducers of the cytokinins generated by the plants. Background released last season on the use of Thiodiazuron at a concentration of 10 ppm applied between 5-7 DDPF showed clear results in increasing the weight and diameter of fruits and an improvement in the proportion of fruit in sizes larger than 28 mm. (Super Jumbo) compared to a control. In turn, it showed favorable results in fruit dry matter, durofel, and without negative effects on color of covering, soluble solids and fruit condition in postharvest. In any case, this type of synthetic cytokinins should not replace the applications of natural cytokinins since they would be a complement as precursors of the action of the plants' own synthesis. It is important to remember that the period of cell division is the most important in the formation of the fruit and it will be at this stage where a strong base of dry matter is formed, a concentration of soluble solids that will be very important when evaluating the condition and quality of the fruit.
Gibberellins.
During cell elongation, the phytohormone that is most closely related to general management at this stage of cherry production is gibberellin. Its mode of action is mainly based on enhancing the cell elongation process in already formed fruits, specifically from the beginning of stage III of fruit development, recognized in practice from the change in color from green to yellow, commonly known as “straw” color. It should be noted that the large endogenous contribution of gibberellins comes from the fruit seed itself.
“It is recognized that the application of gibberellic acid (GA)3) has a positive and direct effect on the increase in fruit size when it is incorporated into the leaves at the cell elongation stage. The doses, based on a known concentration (ppm) will depend, in part, on the cultivar in terms of its susceptibility to cracking, the complexity of having an adequate covering color and the state of charge, since it is well studied that the applications of AG3 and its effect on fruit size could play against fruit splitting (larger size, more splitting) not only due to the effects of rain, but also due to a disorderly development of color and the genetic capacity of each cultivar to provide good fruit size naturally." the expert added.
Applications of AG3, in addition, it generates positive effects on the reduction of epidermal defects in the fruit such as pitting, bruises and roughness. However, recent Chilean studies have shown that high concentrations of gibberellic acid could act unfavorably on the stability of the pedicel tissue, resulting in early dehydration, which is an important quality defect at destination.
