By: Emilio Martínez, R&D Leader Avium; Nicolás Martínez, R&D Technical Support Avium; Carlos Tapia, Technical Director Avium.
The Chinese market is the main destination for Chilean cherries and one of the most relevant attributes for consumers is the size. Due to this and other aspects, under “normal” conditions the Asian market has developed a significant appreciation of Chilean cherries over other suppliers. This is how in recent times the market has evolved to prioritize the quality and condition of the fruit over a rather “generic” product offer. This is why when analyzing the different returns by variety, it can be concluded or rather reaffirmed that the focus of production should be on producing more than 80% cherries over 28 mm in diameter, understanding that with this concept there will always be a percentage of fruit that will also go into smaller size segregations, but ultimately it will be the least at that end.
Large cherries are also perceived as an indicator of the investment and effort of each producer to offer this fruit with a premium seal. It is therefore crucial to understand the importance of size and adapt production strategies to meet the demands of this market and the eventual opening of others.
Cherry producers are always looking to maximize their investment, and as a good business it should be understood in this way, in order to obtain basic strategies to obtain attractive sizes to offer to the market. There are varieties that per se are “calibrators” and others that have a hard time obtaining that potential, therefore, the careful choice of varieties will be caused by the conditions of the site where the orchard is established, the variety/fruit combination and initial training management that impact the potential necessary to achieve productions that ensure the viability of the project.
Thus, among one of the strategies that help improve production in the industry, there are synthetic phytohormone tools with cytokinetic effect, including 6-Benzyladenine (6BA), Thidiazuron (TDZ) and Forchlorfenuron (CPPU). These active ingredients have been shown to have the ability to stimulate fruit growth through cell division in their first stage of growth (Canli et al., 2015; Ferrer et al., 2017; Ouma, 2012). However, the success of their implementation lies in understanding their role in the cherry tree growth cycle and in the appropriate application during key moments of the crop phenology.
The aim of this article is to present some of the good experiences in the rational use of this type of compounds, used to increase fruit size and adjusted to key moments in phenology.
In the above-mentioned context, the use of a 6BA-based product (Product A) formulated with 10% AI has been investigated to demonstrate its stimulating action on cherry size, evaluating relevant production parameters. The research was carried out in two productive orchards located in the commune of Sagrada Familia and Molina in the Maule region. In relation to the plant material used, different treatments were developed in the Santina and Regina varieties, on Colt and Gisela® 12 rootstocks respectively.
The research consisted of five treatments, including a control for effective comparison. Applications were made 7-10 days after full flower (DDPF) and 14-17 DDPF (Table 1).
Table 1. Detail of treatments under investigation for the application of 6BA to improve the size of cherries in cv. Santina and Regina. Tp. 2021-22.
For the productive analysis study, 5 experimental units were selected, with 20 plants per treatment, chosen according to a completely randomized design (CRD). 250 fruits were collected for each treatment to measure their equatorial diameter (mm) and weight (g). Diameter measurements were made with a digital measuring tape, while the individual weight of each fruit was measured using a precision scale. To determine the segregation of sizes (%), 5 repetitions per treatment were used, composed of 50 fruits each, and each fruit was classified according to the commercial packaging categories of Chilean cherries.
Table 2. Segregation of sizes in % in research on the application of 6BA to improve size in cherries in cv. Santina and Regina. Tp. 2021-22.
In the Santina variety (Table 2), there are no significant statistical differences between the control group and the BA treatments, however it can be seen that in the sum of sizes over 28 mm there is a slight increase for the T3 and T4 treatments.
In contrast, in cv. Regina a statistically significant difference is evident in the sum of sizes over 28 mm, this is consistent with the T3 and T4 mentioned above in cv. Santina, where it was possible to show that more than 75% of the cherries treated with BA (T3 and T4) managed to overcome this size barrier, which could be an interesting alternative for strategies to stimulate fruit growth.
Likewise, spraying with TDZ and CPPU has shown significant favorable results in increasing the caliber of cherries. The use of the strategies at the right time between 7 to 10 days after full blossom (DDPF) shows the best performance in this type of phytohormones for the objective of stimulating caliber. According to studies by various researchers, it has been observed that the application of cytokinins in different fruit species should be carried out only once after flowering, in order to stimulate the initial development of the fruits coinciding with the behavior of the endogenous hormonal content (Canli and Pektas, 2015; Guardiola et al., 1993; Wismer et al., 1995).
A study carried out in the 2016-17 season with TDZ where sprays were carried out at two early phenological moments of the species: i) in full flower (PF) and 7 DDPF at a concentration of 5 ppm of ai in each application (10 ppm total) corresponding to T1 and as T2 the strategy was carried out only at 7 DDPF at a concentration of 10 ppm of ai. The above was always contrasted with a control (T0) without growth regulator strategies, revealing that the treatments with TDZ had a better response to the increase in size in most of the 5 varieties studied, however the treatment applied at once, after the 7 DDPF at 10 ppm of ai, is the one that had a better response in improving the size curve.
In the case of the use of CPPU sprays, the same trends could be observed, where applications at a single moment in petal fall (CP), which corresponds to 7-10 DDPF, obtained the best results compared to treatments in more advanced stages positioned in jacket fall (20 DDPF).
Tables 3 and 4 show some of the research carried out with the use of TDZ and CPPU in cherry trees by the R&D team of Avium SpA.
The use of growth regulators is certainly the subject of regular study, offering attractive alternatives within an application program in the crop's production units. By optimizing the application practices of synthetic phytoregulators, producers can increase their productivity and competitiveness in the global cherry market.
Special attention must be paid to the regulation of their use, considering that they comply with all the canons of quality and market requirements regarding the limit of residues of this type of products. In this context, it is understood that some concentrations of use, frequency of application, application times and varieties may not be complying with some standards of residue release of some active ingredients studied.
Chile is well positioned to continue to be a leader in cherry production and meet the growing demand of Asian and global consumers.
Improving cherry production not only has economic implications for producers and the industry as a whole, but also contributes to food security and the country's economy by ensuring a stable supply of nutritious and high-quality foods, so the use of these strategies must be carried out in compliance with the recommendations for use on the label for each particular product and thus safeguard the correct use of these molecules.
Literature.
Canli, F.A., & Pektas, M. (2015). Improving fruit size and quality of low yielding and small fruited pear cultivars with benzyladenine and gibberellin applications. Eur. J. Hortic. Sci, 80(3), 103-108.
Canli, F.A., Sahin, M., Ercisli, S., Yilmaz, O., Temurtas, N., & Pektas, M. (2015). Harvest and postharvest quality of sweet cherry are improved by pre-harvest benzyladenine and benzyladenine plus gibberellin applications. Journal of Applied Botany and Food Quality, 88(1).
Ferrer, C., Martiz, J., Saa, S., & Cautín, R. (2017). Increase in final fruit size of tangor (Citrus reticulata× C. sinensis) cv W. Murcott by application of benzyladenine to flowers. Scientia Horticulturae, 223, 38-43.
Guardiola, JL, Barres, MT, Albert, C., & Garcı́a-Louis, A. (1993). Effects of exogenous growth regulators on fruit development in Citrus unshiu. Annals of Botany, 71(2), 169-176.
Ouma, G. (2012). Fruit thinning with specific reference to citrus species: A review. Agriculture and Biology Journal of North America, 3(4), 175-191.Wismer, PT, Proctor, JTA, & Elfving, DC (1995). Benzyladenine affects cell division and cell size during apple fruit thinning. Journal of the American Society for Horticultural Science, 120(5), 802-807.
