Pollination is the fundamental process for the reproduction and production of any crop. In the case of cherry trees, although they have a very short flowering period, the most important milestones for the formation of seeds and the initial growth of the fruits occur in just a few days, which will define the productive potential of an orchard during the season.
The path from pollination to fertilization involves fundamental processes for the different fruit species. Once the pollination process has taken place, completed by the positioning of the pollen on the stigma of the recipient flower, the fertilization process begins through the creation of the pollen tube where the pollen travels through the stigma and the style before entering the ovary to complete the process.
“The pollination process means the movement of pollen from the anthers of the flower that provide the pollen until the pollen is positioned on the stigma of the pistil of the receiving flower. This process generally has two paths, an anemophilous one, which is a path by wind in a natural way, or an entomophilous one, which is through vectors based on insects, mainly bees in our case, and in the case of southern Chile and cherry crops under forced conditions such as greenhouses or macro tunnels, it is also complemented by the use of bumblebees (or Bombus sp.) that help the movement of this pollen. Although there are other, much more modern techniques that are being developed with respect to pollination, such as electrostatic application of pollen, or artificial movement of pollen with some type of wind, it is still framed in these two large phases of movement, which are vectors and wind in a natural or artificial way. Therefore, that is the pollination process, considering that there must be pollen compatible with the receiving flower.
In the case of self-fertile varieties, the concept of self-fertility is defined as the fact that the pollen is genetically compatible with the flower of the same variety, but not necessarily that it should not be pollinated with some type of system. It is a mistake to think that for self-fertile varieties it is not necessary to use bees; if it is necessary to do so in a much smaller proportion than in varieties that are self-incompatible, it means that the pollen of that variety is not compatible with the flower of the same variety, therefore, a variety that is genetically compatible must be sought in order to be pollinated and fertilized.
In these cases, the standard numbers of bee hives used in Chile to pollinate self-fertile varieties range from 4 to 6 hives per hectare, and for self-incompatible varieties, depending on the number of pollinators and other factors, they could be between 12 and 15 hives per hectare." said Carlos Tapia, technical director of Avium.
In cherry cultivation, the stigmas are receptive after the flower opens and are covered by a conspicuous, viscous-looking secretion where the pollen grains “land”. It is there that they hydrate and germinate, producing a pollen tube for its subsequent development. This entire process in the cherry tree occurs on the first day after pollination itself. After various processes, the pollen tube enters the style of the flower to move through it until it reaches the ovary. The pollen tubes are composed of carbohydrates necessary for their growth from the cells of the transmitting tissue found in the style, which are full of starch (main source of carbohydrates), which are exhausted once the pollen tubes grow. Inside the style, there is intense competition between pollen tubes, with usually two or three of them reaching the ovary, which is conditioned by the complex structure inside the style, and where it leaves less space for the growth of the tubes.
In cherry trees, the pollen tubes that manage to reach the base of the style where the ovary is located take approximately three days after pollination, considering that the environmental temperature plays a fundamental role in the speed of development of the pollen tubes. For fertilization and subsequent setting to take place, only one of the two ovules found in the ovary is required.
In cherry blossoms, different complex processes can be distinguished that develop inside, between the pollen tube and the ovary, and in which the pollen tubes are “stopped” and cannot achieve fertilization of the ovule.
“The fertilization process is the process that once the pollen is positioned on the stigma of the pistil of the flower, it occurs through germination that the pollen generates a duct, which is formed by this germination of the pollen, the so-called pollen tube and this pollen tube descends to reach the ovary to fertilize the ovules. Once the pollen tube reaches to fertilize the ovules, the fertilization process occurs and is independent of the pollination process. What processes positively influence fertilization? The main factor is temperature. At optimal temperatures (between 15° and 22 °C) the growth of the pollen tube is faster therefore it can reach the ovules in less time, considering that the ovules have a short period of viability. For optimal fertilization, the pollen tube must be fertilizing in less time than the viability of the ovule, that is, for example, if the ovules have a viability of three days, the pollen tube must germinate and develop before three days because otherwise, they will not be able to fertilize the ovules and this process is called fertilization. This process is physiologically defined as the effective pollination period (EPP).
Once the fertilization process has successfully occurred, we could say that the fruit setting process begins, which is when the ovary of the pistil of the flower is engulfed and transformed into the final fruit through all the phenological and physiological processes of the plant. Tapia added.
Once the ovules have been fertilized, the process known as fruit setting begins and it waits to complete its three stages of development: cell division, hardening of the stone and cell elongation.
These three processes develop independently and require different nutritional and hormonal needs within the plant, considering that there are cultural tasks that would enhance each of these processes with the aim of achieving maximum productive potential.
Bibliographic references
– Carlos Tapia: personal communication.
– “Cherries, botany, production and uses”- Edited by: José Quero-García, Amy Lezonni, Joanna Pulawska and Gregory Lang.
