Challenges and future of the cherry: from varieties to climate, insights from Chile on today's industry

Analysing all the challenges of the cherry industry in a series of articles may seem pretentious, but it is a way to question, in a holistic way, some of the aspects that seem most relevant in the present and near future.

In this article, Jean Paul Joublan Millan, lists those that may be most apparent for the time being. Firstly, citing those that have been discussed in other analyses, but considering that many others may be transcendental and this article may provide an opportunity to cite and analyse them.

1. Improving the product.
2. Exploiting commercial sales.
3. Consider varietal replacement.

For the latter, there is a wide range of genetic programmes that are promoting varieties with good performance and load in our country. However, there are several challenges that are just as important, if not more so:

1. Incorporate sustainability into cherry production.
2. Improve programmes and management of pests such as Drosophila suzukii and other potentially dangerous species such as Halymorpha halys, for example.
3. Reduce the application of pesticides.
4. Optimise soil management and nutrition.
5. Develop wood disease management protocols and strategies.
6. Incorporate criteria for palatability in new and old varieties.
7. Post-harvest and winter management to reduce the impact of climate change on plant stress.
8. Research into viruses and their consequences as production barriers.
9. Development of virus-free plant certification programmes.
10. Nutrition through new strategies with organic matter and microorganisms.
11. Evaluation of management to reduce the incidence of climate parameters of exception.

Improving the product

This point may seem obvious, but several factors that determine product improvement must be analysed. Everything that concerns the development of fruit quality or product improvement is played out on several levels, both pre-harvest and post-harvest.

Pre-harvest factors can be multiple, but in recent years agro-climatic conditions have clearly complicated the management of production factors to optimise fruit quality. The quality and availability of irrigation water is an issue to be considered.

However, seasonal production is less defined by irrigation under normal conditions. Fruit size and sugar content, under current conditions, are more influenced by water supply in the growing season than they were a few years ago; sufficient moisture should be available at flowering and harvest under normal conditions.

A seasonal water deficit can lead to a calcium deficiency in the fruit and thus to a reduction in firmness. Above all, however, irrigation in the preceding season is of great importance because of its influence on root and bud development as well as on the cherry tree's stress and thus its health.

The following season's production requires a physiologically active leaf surface that needs a minimum of water in summer. With regard to rootstocks, Maxma 14 and Pontaleb can be mentioned, which are less sensitive to water deficit due to their better root system.

Above all, an adequate supply of nutrients from the soil is required, with balanced levels of macro- and microelements. The incorporation of minerals (M1) can occur through the incorporation of organic matter (M2) or microorganisms (M3).

Plant-microorganism and microorganism-microorganism interactions in the soil enable improved biofertilisation behaviour, as in the case of nitrogen fixers and mineralising nutrient binders. These have a biostimulation and bioprotection effect, as well as structuring the soil to achieve greater moisture retention.

The correct evaluation of harvest parameters for each variety is very important and must be well defined. In post-harvest, it is important to define the parameters that represent problems due to the long period of controlled atmosphere storage of the cherry tree. These include the factors that cause browning in cherries and in particular in Regina, where the harvest time and the nutritional status of the plant seem to be the most relevant, but there is still a long way to go before they are fully understood.

Exploiting commercial windows

This has been mentioned a lot, but it is an issue that has several components that can be mentioned. One is the varietal issue, especially with regard to seasonal varieties, on which there is already a lot of research. However, it is worth emphasising one relevant aspect, which is not to repeat what is happening with blueberries, where Peru has significantly increased early blueberries, affecting the profitability of this marketing window.

Another relatively important aspect is the use of European-type greenhouses, e.g. in Lérida, Catalonia, where Cherries Glamour produces cherries of the highest value in Europe.

Quality and varieties such as Kordia, with a higher value than other varieties for later seasons, should not be neglected. The incorporation of varieties with high visual, post-harvest and organoleptic quality is a way to improve profitability in times of higher supply volumes.

Considering varietal substitution

With regard to recently incorporated early varieties, if Santina is chosen as the reference for the harvest period in the northern area, varieties such as Royal Tioga can be harvested 18 days earlier, Nimba 16 days earlier, Brooks 14, Glenn Red 12, Royal Hazel 10 days earlier and Sweet Aryana together with Royal Down can be harvested 8 days earlier. (See Table 1).

Sweet Aryana.

It should be noted that these harvest dates do not take into account the use of any type of mulch. Therefore, if, for example, macro tunnels are added to these orchards to create 'greenhouse' conditions, up to seven days in advance for each variety and the premium is very high compared to other alternatives, it is possible to achieve good profitability by bringing the harvest forward by one week.

New climatic conditions

This point deserves a brief but special analysis because of the great influence it can have on both the yield and the quality of the fruit produced. High temperatures during flowering and after harvesting are likely to become much more frequent in the future. Temperatures of 40°C at harvest time may be possible.

In addition, spring rains, but especially very late frosts, have been observed. For example, in 2015 and 2019, frosts as low as -4°C occurred on 20 and 21 November in the Bio Bí and Ñuble regions. Significant rainfall can be a factor affecting cherry pollination, as pollen breaks down due to an osmotic phenomenon or remains on the ground, preventing pollination.

Dry environment is a problem as well, as it causes the anthers to shed and the pollen to die. Another influencing factor is frost, which reduces pollen germination.

Temperature directly influences germination and pollen tube development. The optimal temperature for pollen tube development is between 22 and 25°C, while at 5°C the pollen tube stops growing. On the other hand, at temperatures above 25°C, when working with plants in a greenhouse, there are difficulties in germination.

Temperatures suitable for bee activity, i.e. between 10 and 12°C, are required for pollen transport (Joublan & Claverie, 2004).

Furthermore, the receptivity of the stigma is preserved for three to five days after the flower opens. According to several authors (Joublan & Claverie, 2004), optimal conditions for pollination after the opening of each flower are preserved for two days. However, since there are differences in flower opening in each tree, the actual pollination period of a tree lasts about four to five days.

Jean Paul Joublan Millan

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