GIRDLING, MATURATION DEGREE AND ETHEPHON ON AZALEA CUTTINGS ESTABLISHMENT

The sector that ranges from cultivation to sale of ornamental species is highlighted in the agribusiness scenario, due to the frequent increase in demand for its products. This importance encourages the exploration of new technologies that allow the development of protocols for the multiplication of species of commercial interest. Thus, the objective of this study was to evaluate and validate the use of girdling, ethephon and the selection of degree of branch maturation as techniques for increasing the establishment of cuttings of Rhododendron simsii Planch. The treatments combining the three study factors were applied to the branches of the parent plants: two levels of girdling (with and without), two levels of application of ethephon at the concentration of 900 mg L-1 (with and without application) and two degrees of maturation (woody and herbaceous). It was found that the presence of branch girdling increased the rate of establishment of cuttings by 43.75%, while the joint use of two techniques, the application of ethephon and the selection of herbaceous cuttings, resulted in an establishment rate 56.25% higher than the average of other treatments. Thus, it can be concluded that both branch girdling and the application of ethephon combined with the use of herbaceous branches can be used as techniques for the greater establishment of cuttings of Rhododendron simsii Planch.


INTRODUCTION
Azalea (Rhododendron simsii Planch.) is an ornamental plant in the Ericaceae family, originating in Asia (Shrestha et al., 2018) and widely cultivated in Brazil (Bezerra et al., 2020). In landscaping, this shrub is commonly used in pots, as well as in gardens, as an isolated plant or as the constituting elements of borders, rows and massifs. Its ornamental value owes to the beauty of its colorful flowers, ranging from white to red, purplish or pinkish, which can be simple or folded and appear in the autumn-winter period (Lorenzi, 2015;Feliciana et al., 2017;Mo et al., 2020).
The propagation of azalea can be sexual or, more commonly, asexual, because of the genetic heterogeneity observed in the seeds (Zaytseva and Novikova, 2018). Traditionally, stem cuttings are used to propagate most Rhododendron species (Eeckhaut et al., 2009). However, its rooting is often difficult, with a small percentage of catching and, consequently, low seedling production (Lone et al., 2010;Li et al., 2017).
The use of cuttings is an important technique applied to the production of seedlings of species of economic interest, such as ornamental, forest and fruit. This method yields plants of high quality, in addition to the multiplication, through cloning, of vegetables with high productive potential or other characteristics demanded by producers and consumers (Georget et al., 2017;Vendruscolo et al., 2017;Wetzstein et al., 2018).
Success of cuttings use will depend on factors intrinsic to the species, as well as external factors that act on the morphophysiological conditions of the mother plants. These conditions may be due to natural changes in the environment, but they can also be caused on purpose by human action, in order to obtain better results. The treatment of parent plants with hormonal and nutritional products has been studied with the objective of increasing rooting levels and the consequent quality of seedlings (Véras et al., 2017;Villanova et al., 2017;Hilgert et al., 2020).
Other established and widely used techniques in the production of vegetable plant seedlings are girdling and selection of the degree of maturation of cuttings. In girdling, the accumulation of photoassimilates and phytohormones in the branch, resulting from the presence of the Malpighi ring, favors the development of roots in the cuttings and, consequently, their establishment. The degree of maturation of the branches can also influence the survival and the emission of new structures; however, this degree will vary according to the species and its characteristics (Lucena et al., 2014;Stuepp et al., 2016;Ferus et al., 2017).
Contrary to the aforementioned techniques, the use of ethephon (2-chloroethyl) phosphonic acid, a synthetic product that precedes ethylene, is contradictory in the asexual production of seedlings. In cutting, ethylene is synthesized when auxins are applied, stimulating the formation and development of roots, thus increasing the percentage of cuttings rooting (Fachinello et al., 2005).
In viticulture, ethephon applied to mother plants prior to cutting collection stimulates rooting, in addition to controlling several other physiological processes related to cellular elongation, enzymatic activity and nutritional status (Szyjewicz et al., 1984;Petri et al., 2016). Some studies point to a positive effect of the application of this compound on the emission characteristics of new shoots and their development (Abreu et al., 2017). This effect is the result of the accumulation of nutrients and reserves, resulting from the induced senescence of the leaves, and its consequent translocation to the buds (Fracaro and Boliani, 2001).
Better results in rooting cuttings of guava (Psidium guajava L.) (Marco et al., 1998) and plum (Prunus salicina Lindl.) were observed using ethephon (Dutra et al., 1997). There are no studies on the use of ethephon and girdling in the treatment of azalea mother plants, although the results have been verified for some horticultural species, mainly woody fruit. In this way, the hypothesis arises that these techniques can be applied to floriculture.
Therefore, it appears that the isolated use of techniques to increase success in the formation of seedlings by cutting is frequently studied. However, we lack information about the joint use of these techniques, which can bring better results. Thus, the objective of this study was to evaluate and validate the use of girdling, ethephon and the selection of degree of branch maturation as techniques for increasing the establishment of cuttings of Rhododendron simsii Planch.

MATERIAL AND METHODS
The branches used for the study were collected from azalea plants located at the School of Agronomy of the Federal University of Goiás, in the city of Goiânia, located in the central region of the state of Goiás, with geographical coordinates of 16° 40' S and 49° 15' W, and an altitude of 750 m.
The test was carried out in a randomized block design in a 2x2x2 factorial scheme, totaling eight treatments. The treatments combining the three study factors were applied to the branches of the parent plants: two levels of girdling (with and without), two levels of ethephon (with and without application) and two levels of branch maturation (woody and herbaceous). The treatments were applied to five branches, about 1.20 m long. Each experimental unit was composed of five cuttings.
Girdling was executed at the base of the branch, close to the neck, using a pocket knife, on March 27, 2017, seven days before the cuttings were removed, and consisted of the total elimination of a bark ring approximately 1 cm wide and 1 mm deep. The idea was to break the phloem without damaging the xylem.
Ethephon (2-chloroethyl) phosphonic acid (Ethrel ® ) was applied to the respective branches after girdling, by spraying asolution of 900 mg L -1 of the active ingredient, common for vine defoliation in the region, reaching all branch leaves and using a manual sprayer with a flow of 10 mL s -1 . Seven days after application, when there was a total fall of leaves applied with ethephon, the branches were cut and divided into cuttings 10 cm long (Feliciana et al., 2017). These cuttings were separated into herbaceous or woody, by observing the absence and presence of dark colored lignified cortex, respectively.
The cuttings were planted in plastic trays with a capacity of 500 mL, filled with commercial peat substrate (Plantmax ® ), previously moistened, burying half the stake. Optimal conditions for the growth of Rhododendron species range from 18-25 °C and high air humidity (Li et al., 2020), so the whole plant was taken to the germination chamber with a temperature of 25 ± 1 °C, relative humidity of 90% and a photoperiod of 12h, for 25 days, without the need to replace the water in the substrate. After this period, the cuttings were removed from the substrate and visually evaluated for their establishment, verified when there was joint emission of aerial structures (shoots) and roots.
The data was submitted to analysis of variance and compared by least significant difference (LSD) test, with a probability of 5%.

RESULTS AND DISCUSSION
No interaction was observed between the joint use of girdling,ethefon and the degree of maturation of the cuttings. However, branch girdling had an isolated effect, and there was an interaction between ethephon application and the maturation of the cuttings on the establishment index (Table 1).
It was found that the presence of branch girdling increased the establishment of azalea cuttings by 43.75% (Figure 1), characterized by the joint development of root structures and shoots. Branch girdlingacts to interrupt the translocation of sap by the phloem, preventing the downward movement of photoassimilates and nutrients towards the plant's root system. This temporarily provides the accumulation of carbohydrates and hormones in the aerial portion of the vegetable (Mehouachi et al., 2009). Fachinello et al. (1988), working with apple rootstock matrices "Malling-Merton 1061", concluded that the girdling also stimulated the rooting of the cuttings. The authors found a greater accumulation of total soluble sugars in these branches, which is the only source of carbohydrates that can provide energy for the formation and development of roots.In addition to providing a greater accumulation of starch and sugars, girdlingallowed the addition of rooting cofactors such as phenolic compounds and polyamines in olive cuttings, increasing the rooting potential of this species (Denaxa et al., 2021).
The combined use of two techniques-the application of ethephon and the selection of herbaceous cuttings in azalea-resulted in an establishment rate 56.25% higher than the average of the other treatments (Figure 2). Similar results have been reported by Dhua et al. (1982), applying ethephon to guava branches (Psidium guajava L.), collecting herbaceous cuttings (from the ends of the branches) after seven days, treating or not treating plants with indolbutyric acid (IBA). The authors found that rooting was around 100%better in cuttings that received treatment with ethephon and, later, with IBA. Véras et al. (2018) also observed an increase in the percentage of rooting and the number of roots on umbuzeiro cuttings (Spondias tuberosa Arruda), when combining ethephon and with AIB. In addition, there are reports that ethylene acts as an important stimulator of adventitious root formation in Petunia hybrida (Hook. Fil.) Vilm by Druege et al. (2014), and in marigold (Tagetes erecta L.) (Jin et al., 2017).
In the propagation of azalea for commercial purposes, according to Chalfun et al. (1997), the best results are obtained with the use of semi-hardwood cuttings, since the woody ones have a higher degree of lignification, making rooting difficult. In addition, the chemical composition of the tissue varies along the branch, causing differences in rooting in cuttings from different parts of it (Santos et al., 2016). Therefore, the higher rate of establishment, in herbaceous cuttings, may be influenced by the levels of phenolic compounds and carbohydrates present in them, due to the translocation of the photoassimilates present in the leaves, at the time of senescence induced in these cuttingswith the use of ethephon.
Considering the results, we infer that the treatments evaluated in this study have the potential to be used for    azalea. The advancement of the methodology depends mainly on the establishment of ethephon dosages, suitable for the various ornamental species grown.

CONCLUSION
Branch girdling and the application of ethephon combined with the use of herbaceous branches can be used as techniques for the greater establishment of azalea cuttings.

AUTHOR CONTRIBUTION
EPV: project idea, formulation of the aims, research planning; experiment performing, text writing. FRS: collected the data and analysis, text writing and critical review. LFCC: experiment performing, collected the data, text writing and critical review. AS: experiment performing, data analysis and statistics, text writing. LLP: data analysis, text writing and critical review.

ACKNOWLEDGMENTS
This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior -Brasil (CAPES) Finance Code 001.