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INTRODUCTION
Greater concern for healthy habits has continuously increased demand for products with functional characteristics that have high levels of vitamins, minerals, and antioxidants. In this tendency, the introduction of native fruit species in industrial processes is observed, previously cultivated only on a small scale. Jabuticaba (Plinia spp.) fruits are rich in sugars, vitamins and other compounds that are beneficial to health and pleasant to the palate (Kosera Neto et al., 2018).
Despite the organoleptic characteristics of these fruits, which have been increasingly explored by agribusinesses, the large mass of seeds in relation to the total mass of the fruits decreases their processed uses. Technologies that increase pulp yield are sought. Gibberellic acid is used in the production of parthenocarpic fruits (Pandolfini, 2009), such as the atemoia (Pereira et al., 2014), pear (Sezerino and Orth, 2015) and pepper (Tofanelli et al., 2003).
The application of gibberellins during flowering replaces the active role of seeds that are aborted because of adverse climatic conditions or lack of pollination (Soares et al., 2001; Semensato et al., 2020). However, despite the fact that gibberellin is the main active hormone regulating flowering, applications with high concentrations cause inhibition (Silva et al., 2017). In addition, the effectiveness of exogenous applications of gibberellin depends on the intrinsic factors of each species (Tofanelli et al., 2003; Pereira et al., 2014; Sezerino and Orth, 2015).
This study aimed to evaluate the development and organoleptic quality of jaboticaba fruits as a function of exogenous applications of gibberellic acid on the stem of plants in three reproductive stages.
MATERIALS AND METHODS
This experiment was installed in August of 2017 in a commercial orchard located in the municipality of Hidrolândia-GO, Brazil. The geographical coordinates are 16º52’27” S and 42º19’25” W. According to the Köppen classification, the climate is tropical Aw (warm and semi-humid, with a well-defined dry season from May to October) (Cardoso et al., 2014). The average altitude is 814 m, with an average annual temperature of 22.8°C and an average rainfall of 1,411 mm year-1. For 2016, climatic data were obtained from a meteorological station in the municipality of Hidrolândia, about 8 km from the experiment area, for the temperature and precipitation variations (Fig. 1).
Figure 1 Temperature and precipitation averages in the municipality of Hidrolândia-GO during the study period in 2016.
This experiment was conducted in an area containing 'Pingo-de-mel' jabuticaba trees (Plinia jabuticaba) (Vilela et al., 2012) with a free-standing cultivation in soil with a sandy-clay texture, at 3×3 m spacing, irrigated by row and fertilized every two years with 1 kg of chicken manure per plant. For this experiment, six 18-year-old jabuticaba trees were randomly selected. The chemical analysis of the soil showed, at a depth of 0-0.2 m, levels of Ca2+: 1.7 cmolc dm-3, Mg2+: 0.4 cmolc dm-3, K+: 28.0 mg dm-3, P (Mehlich I): 1.87 mg dm-3, Al3+: 0.3 cmolc dm-3, pH (CaCl2): 4.51, CTC: 5.17 cmolc dm-3, and V: 41.99%. The granulometric analysis of the soil revealed 26 g kg-1 of clay, 18 g kg-1 of sand and 56 g kg-1 of silt at a depth of 0-0.2 m.
The treatments included the combination of four concentrations of gibberellic acid (0, 50, 100 and 200 mg L-1) applied on jabuticaba branches in three reproductive phenological stages (flower buds; anthesis and post-flowering). The experiment design used randomized blocks in a factorial scheme (4×3) with six replications. Each experiment unit consisted of two 50 cm branches per tree (block) that were evaluated during each phenological stage. A solution containing the growth regulator was applied with a manual sprayer (20 mL/branch).
To define the phenological stages, the following parameters were adopted: flower buds - moment when swollen buds were observed; anthesis - observation of flower opening in more than 80% of flower buds; post-flowering - when small-green fruits appeared during the first stage of development in more than 80% of the floral structures.
After ripening, 15 fruits were randomly harvested from each plot for the quality assessment and then taken to the laboratory to be evaluated. The analyzed variables were: fresh fruit weight, fresh seed weight and fresh peel weight, obtained with an analytical scale; the number of seeds was counted; the longitudinal diameter and transversal diameter were measured with a digital caliper; the soluble solids were measured with an analogical refractometer; the titratable acidity was obtained with titration with a NaOH solution (1M), along with the ratio (ratio between soluble solids and titratable acidity).
The data were submitted to preliminary tests of normality and homoscedasticity and then to analysis of variance. The averages of the quantitative factor levels and concentrations of gibberellic acid were subjected to polynomial regression analysis. The means of the qualitative factor and phenophases were compared with each other with the Tukey test at 5%. The statistical program was Sisvar 5.6 (Ferreira, 2014).
RESULTS AND DISCUSSION
There was no interaction between the factors, and the application of gibberellic acid did not influence the fruit fresh weight, regardless of the phenological stage in which the application occurred. However, for the other variables, there were significant differences between the means obtained with the treatments (Tab. 1).
Table 1.Fresh fruit weight (FFW), longitudinal diameter (LD), transversal diameter (TD), fresh seed weight (FSEW), fresh peel weight (FSW) and number of seeds (NS) in fruits from jabuticaba trees treated with gibberellic acid in different phenological stages.
| Phenophase | FFW (g) | LD (mm) | TD (mm) | FSEW (g) | FSW (g) | NS ( - ) |
|---|---|---|---|---|---|---|
| Flower-buds | 3.43 a | 16.65 a | 16.66 a | 1.19 a | 0.26 a | 1.72 a |
| Anthesis | 3.13 a | 14.45 b | 14.46 b | 1.05 b | 0.18 b | 1.28 b |
| Post-flowering | 3.46 a | 16.32 ab | 16.30 ab | 1.13 ab | 0.22 b | 1.37 b |
| LSD | 0.37 | 1.93 | 1.92 | 0.13 | 0.04 | 0.15 |
| CV% | 16.35 | 17.53 | 17.43 | 17.09 | 25.89 | 14.33 |
Means followed by the same letter in a column do not differ according to Tukey's test at 5% probability. LSD = Least significant difference; CV = Coefficient of variation.
The longitudinal and transverse diameters and fresh peel mass were higher in the fruits treated during the bud phenophase; however, they did not differ from the fruits that received the treatment during the post-flowering phenophase (Tab. 1). As compared to the fruits treated in anthesis, applications of gibberellic acid during the bud phenophase increased the characteristics longitudinal diameter, transversal diameter, and fresh peel mass by 15.23, 15.21 and 13.33%, respectively.
The application of gibberellic acid during the anthesis and post-flowering phenophases significantly decreased the fresh mass and number of seeds (Tab. 1). Under these conditions, the applications during anthesis decreased the fresh weight and the number of seeds by 30.77 and 25.58%, respectively, as compared to the applications on flower buds. As compared to the applications on flower buds, the post-flowering applications reduced these characteristics by 15.39 and 20.35%, respectively.
There was a linear decrease in the variables fruit fresh weight, peel fresh weight and seed fresh weight as the concentrations of gibberellic acid increased, up to the maximum concentration of 200 mg L-1 (Fig. 2). At this concentration, the reduction was 16.14, 16.50 and 24.32%, respectively, for the characteristics of fresh fruit mass, fresh peel mass and fresh seed mass. The reduction in the fresh weight of the peels and seeds was responsible for 50% of the reduction in fruit fresh weight.
Figure 2 Fruit fresh weight (A), peel fresh weight (B), seed fresh weight (C) and number of seeds (D) of jabuticaba fruits treated with increasing concentrations of gibberellic acid.
A decrease in fruit fresh mass may be related to greater fruit fixation provided by the action of gibberellic acid on the production of proteolytic enzymes (Vieira et al., 2008a). These enzymes are responsible for the release of tryptophan, which in turn acts as an indolacetic acid precursor, which prevents the formation of the abscission layer that connects fruits to plants (Pires and Botelho, 2001).
In addition, the decrease in the mass of the fruits, peels and seeds and the increase in the number of seeds with the increases concentrations of gibberellic acid may have resulted from the inverse relationship between cell size and number of cells because applications of this phytohormone increase cell division activity while decreasing cell volume, resulting in a compensatory effect for some species, such as grapes (Vieira et al., 2008b).
There were no effects from the application of gibberellic acid in the different phenophases for the organoleptic characteristics titratable acidity, soluble solids and ratio (Tab. 2). However, the application of phytohormone during anthesis and post-flowering increased pulp yield by 21.43 and 20.31%, respectively, as compared to the flower bud phenophase.
Table 2 Titratable acidity (TA), soluble solids (SS), ratio and pulp yield (PY) in fruits from jabuticaba trees treated with gibberellic acid in different phenological stages. Hidrolândia-GO, 2016.
| Phenophase | TA (mg citric acid/100 g) | SS (°Brix) | Ratio (-) | PY (%) |
|---|---|---|---|---|
| Flower-buds | 1.23 a | 12.04 a | 11.43 a | 50.08 b |
| Anthesis | 1.03 a | 13.17 a | 15.71 a | 60.81 a |
| Post-flowering | 1.06 a | 12.68 a | 14.83 a | 60.25 a |
| LSD | 0.24 | 1.16 | 4.67 | 5.03 |
| CV% | 30.69 | 13.24 | 48.02 | 12.6 |
Means followed by the same letter in a columns do not differ according to Tukey's test at 5% probability. LSD = Least significant difference; CV = Coefficient of variation.
For the pulp yield, a linear and increasing response was obtained for the concentrations of gibberellic acid (Fig. 3). The increase in the phytohormone concentrations, up to a concentration of 200 mg L-1, resulted in an increase in this characteristic of 12.58%, as compared to the control treatment, which did not have an application of gibberellic acid.
Figure 3 Pulp yield of jabuticaba fruits treated with increasing concentrations of gibberellic acid.
Exogenous applications of gibberellic acid suppress seminal phytohormone production activity (Tecchio et al., 2009), which is responsible for the formation and distribution of fruit composition through cell division and elongation (Taiz et al., 2017). Increasing concentrations of gibberellic acid result in seed atrophy, which have their functionality reduced by the presence of the synthetic hormone, which starts to play the role of the natural hormone (Pereira et al., 2014). Despite inhibiting the development of seeds, this hormone supplies their activities, maintaining the plant's capacity to accumulate sugars and properly develop fruit size (Taiz et al., 2017).
CONCLUSION
Exogenous applications of gibberellic acid, up to a concentration of 200 mg L-1, during anthesis or post-flowering improve the industrial characteristics of jabuticaba fruits, increasing pulp yield without affecting quality.
This is a promising technique for increasing the use of this species in industrial processes, opening the possibility for applications on other native species.
