The establishment of orchards must consider the climatic requirements and the genetic compatibility of the varieties to ensure the fertilization of the fruits. The flowering time can be brought forward or delayed by chemical or physical treatments, which helps to better market the fruit and manage the orchard.
In Japan, between the months of February and May, Hanami is performed, a tradition that honors the sakura or blossoming of cherry trees. During this period, families and friends go to the different parks of the country to share food while contemplating the beauty of the advance of anthesis (Figure 1). Every year, the sakurazensen or "cherry blossom front" is announced by the Japan Meteorological Agency, whose estimate is made based on the monitoring of reference trees and the behavior of temperatures. In past centuries, sakura indicated the beginning of spring, so it was safe to start sowing rice. Today, this tradition is an instance of reflection on how beautiful, fragile and ephemeral life is and the beginning of a new cycle.
In Chile, the cherry tree is the most important and profitable fruit species at the moment. Technological development has made it possible to influence the time of flowering, which can be brought forward or delayed, which directly affects the harvest date of the fruit. The displacement of the bloom is made as a function of the New Year in China, which is celebrated the second new moon after the winter solstice of the northern hemisphere. This forces the largest supply of cherries to be scheduled in the run-up to this holiday, when it is the period of greatest demand and valuation of this product in that market.
Next, some physiological aspects of cherry blossom will be analyzed, including agronomic management to influence their phenological displacement. Also, the transfer of pollen and how to promote the fertilization of the fruits will be reviewed.
FLORAL INDUCTION AND DIFFERENTIATION
Floral induction in cherry trees occurs around the harvest period of the fruit (November and December) and is influenced by climatic factors (length of the day and temperature), physiological factors (hormones and carbohydrate availability) and, in some cases, situations of abiotic stress (e.g. resource constraints) that prioritize the reproductive growth of trees.
Floral differentiation begins in late summer and the fall months, continues slowly during the winter recess, and culminates with the opening of flowers (anthesis) in spring (Figure 2). In the early stages of floral differentiation, the process can be altered by situations of high thermal stress in the buds, generating malformations that will give rise to double fruits or with open sutures. To prevent this, during the post-harvest of the orchards, the hydric, nutritional and sanitary status of the trees must continue to be safeguarded, which prevents them from having physiological limitations in the face of heat waves in summer.
In addition, strategies to reduce the temperature of the foliage can be used, such as the use of shade nets, high watering and sun blocks of the kaolinite type.
WINTER BREAK AND PHENOLOGICAL BEHAVIOR
During autumn and the first half of winter, the flower buds are in a state of endodormancy whose overcoming is limited by the need for a time of exposure to low temperatures (winter cold).
After this requirement is satisfied, the buds go to a state of eco-dormancy, with flowering being conditioned to the occurrence of a prolonged period with higher temperatures (heat requirement).
Winter cold and heat requirements are different between varieties and can change according to the conditioning of trees between agroclimatic zones and the behavior of environmental conditions during bud formation. Table 1 shows a compilation of the cold and heat requirements for overcoming the winter recess of the main cultivars present in Chile, evaluated in different seasons and locations around the world.
The wide variability of climatic antecedents available for the same variety and the little information developed for the new genetic material introduced to the country, makes it difficult to guide the establishment of new cherry tree plantations in the different agroclimatic zones of Chile. On the other hand, the occurrence of increasingly warm environmental conditions has made the representativeness of the models for overcoming the winter recess uncertain, not achieving, in some cases, an appropriate prediction of the phenological behavior of the trees.
In this context, the Pomaceae Center of the University of Talca is executing the project "Artificial intelligence applied to the monitoring of the behavior of new cultivars of cherry and apple trees in potential productive areas of the Maule Region" (Bip Code 40.047.262-0), an initiative supported by the Innovation Fund for Competitiveness (FIC) of the Regional Government of Maule, which seeks to classify the productive potential of these two species in different areas of Maule and develop indicators of agroclimatic requirements for overcoming dormancy and predicting phenological states. The results of the project hope to provide more information on the behavior of recently introduced cultivars, collaborating with the success of new plantations, maximizing their fruit production in the following days.
The flowers of the cherry tree are simple, hermaphroditic, white, grouped in corymbs from 1 to 5. The inflorescences can be formed either in floral buds located at the base of 1-year-old woods (isolated buds) or in darts on wood two or more years old (dart buds).
