ABSTRACT
Considering that tamarind (Tamarindus indica L.), an exotic fruit in Brazil, is appreciated in natura consumption and has been highlighted by its nutritional and pharmaceutical characteristics, its application in medicines available in the market due its long period of freshness has become an obstacle to the commercial cultivation of this fruit; therefore, the method of propagation by air-layering can solve this problem. Thus, the objective of this work was to evaluate the influence of substrates and the use of indolebutyric acid (IBA) on the production of seedlings by tamarind air-layering method. For this purpose, commercial organic compound, coconut powder and sphagnum were used to make the air-layering and IBA concentrations (500, 750, 1000 and 1250 mg L-1). The experimental design was a randomized complete block, in a 3 × 5 factorial scheme, containing 10 blocks, each plant being considered a block, with 4 replicates (air-layering) per block, distributed in the plants quadrants. Influence of the substrates and IBA concentrations used for the rooting of tamarind air-layering was observed, with a significant interaction of these factors obtained in the evaluated variables. Thus, it can be concluded that propagation by the method of air-layering is viable. For organic compound and coconut powder, the concentrations of 500 and 1000 mg L-1 IBA, respectively, may improve the results obtained by air-layering. With the use of sphagnum as substrate, the use of 500 mg L-1 IBA to maximize the results is indicated in this method.
Key words: Fruits, propagation materials, Tamarindus indica L., tropical fruits, seedling production.
Tamarind tree (Tamarindus indica L.), an exotic fruit tree in Brazil, stands out among non-traditional tropical fruits trees, due to the nutritional and pharmacological properties of all parts of the plant (Khanzada et al., 2008; Havinga et al., 2010). The potential of exotic tropical fruits has contributed to the agroindustry and pharmacological market, due to the nutraceutical properties and added value of the products from these species which are not sufficiently explored.
Tamarind fruit has an acid flavor mesocarp rich in vitamin C, and is used in national and international popular cuisine, in the production of jellies, juices, ice creams and fresh market. In addition to the nutritional properties, tamarind seeds are rich in essential oils with laxative, antimicrobial, antispasmodic, anti-inflammatory and antidiabetic functions (Ali and Shah, 2010; Escalona et al., 2010; Amado et al., 2011), which are important characteristics for the pharmaceutical market.
From this information, there is a need for the creation of germplasm banks and the production of seedlings, for the maintenance and formation of commercial orchards of this fruit. In the literature, it is reported that the production of seedlings of the tamarind tree is predominantly by seeds, and the plants cultivated from this method have a long period of juvenility (Ajiboye et al., 2011; El-Siddig et al., 2006).
Faced with this difficulty, propagation methods are fundamental in the production of seedlings of this species, and have become a line of research interest. Among the methods, air-layering is notable for integrating the rooting of a portion of the branch still connected to the matrix plant and improving the conditions for rhizogenesis (Dutra et al., 2012a). This type of propagation is feasible in several non-traditional fruits such as urucum (Montovani et al., 2007), marmelo (Pio et al., 2007), umbu (Dutra et al., 2012a) and litchi, which are the most used systems for commercial production of these species.
The success of this technique can be enhanced by the use of organic substrates, aiming to guarantee structural support, water retention, nutrient supply and the possibility of gas exchange, thus allowing the development of roots and quality seedling (Dutra et al., 2012b). Traditionally, sphagnum is used as a substrate in air-layering, due to its high water retention capacity and good aeration (Bitencourt et al., 2007). However, other alternative substrates, such as coconut powder and organic compound have been used (Dutra et al., 2012a) to search for easy availability of the seedlings producer and physico-chemical properties that accelerate the rooting of air-layering.
Besides the use of substrates as a factor to improve rhizogenesis, the application of plant regulators can also help in this process, especially exogenous synthetic auxins such as indol-3-butyric acid, which provides good results in air-layering rooting used in the propagation of fruit, ornamental and tree plants (Sasso et al., 2010; Chagas et al., 2012; Dutra et al., 2012a).
In view of the aforementioned, the objective of this work was to evaluate the influence of substrates and the use of indole-3-butyric acid (IBA) on air-layering rooting of tamarind tree for commercial production of seedlings.
The experiment was carried out from August to November in 10-year-old tamarind trees located in Ilha Solteira/SP (20°24'04" S latitude, 51°20'55" W longitude and 320 m altitude). The climate of the region, according to Köeppen's classification (1948), is Aw type, tropical with dry winter season, presenting average annual temperature of ± 24.5°C, annual rainfall of ± 1,232 mm and air relative humidity of the ± 64.8%. The climatic conditions during the period of the experiment are shown in Figure 1.
The air-layering was randomly performed in the four quadrants of the tamarind plants, using branches with 5 mm diameter. The branches were ringed with the aid of ringing scissors all around the perimeter, at a distance of 40 cm from the apical end. At the annealed site, the concentrations of indole-3-butyric acid (500, 750, 1000 and 1250 mg L-1) prepared in hydroalcoholic solution were applied with a brush.
To create a microclimate around the lesion favorable for the development of roots, the air-layering was wrapped with transparent polyethylene (PVC) bag containing the substrate and tied with nylon clamps at both ends to prevent its dehydration. Also, in this sense, the air-layering were moistened weekly with 15 ml distilled water.
Approximately 300 g of the following substrates were used in the preparation of air-layering: Organic compound based on Pinus bark, coconut powder, vermiculite, peat, charcoal, NPK and micronutrients (Basaplant®), sphagnum and coconut powder. The sphagnum was immersed for 24 h for water absorption and the other substrates were moistened with deionized water during the experimental implantation for easy handling.
The control treatment was done using branches of 5 mm diameter, ringed around the perimeter, with no IBA application and involving the substrates: organic compound, sphagnum and coconut powder. The experimental design was a randomized complete block in a 3 × 5 factorial scheme (substrates × IBA concentrations), containing 10 blocks, with each plant being considered as a block, and with 4 replicates (air-layering) per block distributed in the plants quadrants. As no block effect occurred, the experiment was analyzed as a completely randomized design.
The evaluations were done 90 days after the installation of the air-layering by collecting the following variables: 1) Callus formation (%): this evaluates the number of air-layering that form callus in the ring region; 2) rooted air-layering (%): it evaluates the number of air-layering with at least one root with more than 1 cm; 3) root length (cm); 4) number of roots and root dry matter (g). The averages obtained were subjected to the Dunnet test at a 5% probability, using SAS® v. 9.4 and analysis regression and Tukey test using SISVAR 5.3® (Ferreira, 2007).
In Table 1, there is interaction between the factors tested and the overall averages for the evaluated variables, with significant statistical interaction between the substrates and IBA concentrations. However, in some Brazilian fruits species such as umbu (Spondias tuberosa Arr. Cam.), this type of result was not observed (Dutra et al., 2012a). For comparison of treatments with the control treatments, Dunnet test was performed; therefore, in Table 2, it is observed that for root dry matter, results were significantly different from the control treatment in the IBA concentrations: 500, 750 and 1000 mg L-1 with organic compound. The air-layering performed with sphagnum and IBA presented for root dry matter at concentrations of 500, 750, 1000 and 1250 mg L-1 had significant difference compared to the control. In coconut powder substrate, the concentration of 1000 mg L-1 of IBA provided significant difference in air-layering for root and number of roots; however, the root dry matter differed from the control treatment only at 750, 1000 and 1250 mg L-1 concentrations.
The sphagnum, as observed in this work, is the most indicated substrate for the production of seedlings, obtaining satisfactory results both as a control treatment and with the use of IBA. The same result was reported for ume (Prunus mume Sieb & Zucc) (Chagas et al., 2012), marmelo (Chaenomeles sinensis L.) (Pio et al., 2007) and jabuticaba (Plinia cauliflora) to provide a higher percentage of rooted air-layering. Lins et al. (2015) stated that in litchi, this substrate also presented the best results for this variable, without using plant regulators. For interaction between the factors, the analysis of variance in the regression for IBA doses was performed. For all variables analyzed, the regression deviation was not significant, showing that the model found is adequate.
As reported by Hartmann et al. (2011), for the initiation of adventitious roots, the divisions of the first root-initiating cells are of great importance for the presence of auxins, whether endogenous or exogenous. The use of auxins such as IBA is known to promote the development of adventitious roots, uniformity and success of rooting (Hartmann et al., 2011), and the tested concentrations influenced the percentage of air-layering rooting, number, length and dry matter of the root system (Figures 2 and 3).
Thus, it is observed that for the organic compound, the percentage of rooting (Figure 2a) and the number of roots (Figure 2b) of the air-layers showed descending linear regression with respect to the increase of IBA concentrations of 500 mg L-1 which provided the highest means for these variables.
In the quadratic equation of the sphagnum treatments, the minimum point observed for rooted air-layering percentage and number of roots was 925 mg L-1, providing 30.75% (Figure 2a) and 915.39 mg L-1 with 0.32 roots (Figure 2b), respectively. The maximum point observed in the quadratic equations in treatments with coconut powder was 975 mg L-1 IBA with 85.25% of rooted air-layering (Figure 2a) and 1013.64 mg L-1 IBA with 2.46 roots formed (Figure 2b).
In Figure 3a, it is noted that the air-layering made of organic compounds with increasing concentrations of IBA linearly decreased the root length, and 500 mg L-1 of this regulator provided the greatest value for this variable. However, the dry matter of the roots adapted to quadratic regression, with the concentrations of 500 and 750 mg L-1 IBA (Figure 3b) being the most suitable for the addition of mass in the roots of tamarind air-layering.
For both length and dry matter of the roots in this experiment, the data were adjusted to quadratic regression, with the minimum points observed as 913.79 mg L-1 IBA, 1.86 cm long (Figure 3a) and 760 mg L-1 IBA with 0.23 g dry matter of the roots (Figure 3b).
The use of coconut powder as substrate with increasing concentrations of IBA linearly increased root length and quadratic root dry matter. The highest root length in this substrate was observed at the concentration of 1000 mg L-1 IBA (Figure 3a) and the maximum point of 900 mg L-1 IBA provided 0.03 g of root dry matter (Figure 3b).
Smarsi et al. (2008) reported that organic substrates also had favorable results in the development of the root system in litchi air-layering, which was not expected since sphagnum is the most recommended for this type of propagation in this species. As observed in this experiment, in each substrate, the results obtained with the application of IBA provided different means (Table 3).
The organic compound favored the root development because it has nutritional supplements (NPK and micronutrients) as a source of nutrients for the roots growth and accumulation of dry matter. In this work, this substrate obtained higher values for the evaluated variables when low concentration of IBA (500 mg L-1) was used (Figure 4a).
The use of coconut powder as a substrate for seedling production has been growing in the fruit growing sector due to its high porosity, high potential for moisture retention and biodegradability, even though it does not have a high nutritional content such as organic matter (Lins et al., 2015). The same author did not observe good results for this variable when coconut powder was compared with sphagnum in the litchi air-layering, demonstrating that this substrate was also not effective in this method. However, the concentration of 1000 mg L-1 of IBA provided good results in the tamarind air-layering when coconut powder was used (Figure 4b).
Sphagnum favored the root development at the 500 mg L-1 IBA (Figure 4c), corroborating with the results of Lins et al. (2015) who observed that sphagnum provided greater number and length of roots in litchi air-layering. Dutra et al. (2012a) affirmed that this favoring is important, since the quality of the root system directly influences the survival of the seedlings in the field, especially in less favorable periods.
The good results obtained with the use of sphagnum in the tamarind tree, besides the physical characteristics of the substrate and the use of IBA to promote rooting, are also correlated to the photosynthetic products such as carbohydrates produced by the plant. The availability and use of these substances by the branches favors rooting, since instead of being redirected to other areas such as for flowering and fruiting, these compounds are used by the cells to develop the roots (Maurya et al., 2013). It is worth mentioning that the tamarind plants were in excellent cultivation conditions, well-nourished and with availability of water in the soil, which are influential characteristics in the good rooting of air-layering. This difference in rooting in the substrates and IBA concentrations tested has a great applicability for the producer, since the latter may have options to perform the air-layering according to the availability of the substrate in the region. Also, the efficiency of the air-layering can be correlated with the period that the propagation was done. Maurya et al. (2013) reported that the increase in temperature, relative humidity and the beginning of precipitation during the period of air-layering can provide plant exposure to a continuous supply of water, avoiding dehydration of the branches and positively influencing rhizogenesis.
In addition to influence of availability of water on the rooting of air-layering, Hartmann et al. (2011) reported that increase in temperature favors cell division, thus helping in root formation, which indicates that the season may have been favorable for the propagation of tamarind tree by this method due to the increase in temperature and beginning of the rainy season in the region (Figure 1).
Propagation using the method of air-layering is viable. For organic compound and coconut powder, the concentrations of 500 and 1000 mg L-1 of IBA, respectively may improve the results obtained by air-layering. With the use of sphagnum as substrate, 500 mg L-1 of IBA is indicated to maximize the results in this method.
The authors have not declared any conflict of interests.
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