Post-harvest characterization of strawberry hybrids obtained from the crossing between commercial cultivars

Copyright: All the contents of this journal, except where otherwise noted, is licensed under a Creative Commons Attribution License. Caracterização pós-colheita de híbridos de morangueiro obtidos do cruzamento entre cultivares comerciais Abstract The lack of programs to improve the strawberry crop in Brazil has led to a growing increase in the use of seedlings imported from Chile, which leads to a certain dependence of imported material on the part of the producers and increases the production even more, since the producers have. This proves even more the need for the development of cultivars adapted to the local conditions of cultivation. In this sense, the aim was to evaluate the post-harvest of fruits of 15 hybrids of strawberry obtained from the cross between commercial cultivars, in order to select the materials with chemical quality superior to the cultivars most planted in Brazil. The contents of soluble solids, titratable acidity, ratio, vitamin C, anthocyanins and phenol were evaluated. The characterization of strawberry hybrids indicated that the RVFS 13-07, RVFS 13-24, RVCS 13-07, RVCS 13-10 and RVCA 13-08 materials stood out in post-harvest evaluations, with higher levels of functional compounds (vitamin C, anthocyanins and phenolics) and higher values of quality parameters (soluble solids, titratable acidity and ratio), important characteristics for the in natura consumption or for use by the industry. These hybrids were shown to be promising to continue the crop breeding program by demonstrating that they carried characteristics of interest for intraspecific crosses. The values obtained for the analyzed characteristics were higher than the values found in the literature for the cultivars most planted and consumed in Brazil and in the World, which demonstrates the efficiency in the selection process.


Introduction
In the world context, it is estimated that strawberry production has doubled in the last decade and in 2014 reached more than 8 million tons (FAOSTAT, 2014).Among the Brazilian states, the largest comprises Minas Gerais (40,245 t), Rio Grande do Sul (9,819 t), Paraná (6,265 t) and São Paulo (5,030 t) (GUIMARÃES et al., 2015).The strawberry crop in the State of Paraná produced in the harvest of 2015 around 22.64 thousand tons, with gross value of the production -GVP of R$ 164.15 million.
The strawberry genetic improvement in Brazil began in 1941 at the Agronomic Institute of Campinas-SP and in 1950 at the Experimental Station of Pelotas-RS, now Embrapa Clima Temperado.Several of the materials used by these programs were obtained from the importation of seedlings and achenes from genetic improvement programs in the United States.However, from the 1990s, genetically improved cultivars from international programs were introduced with great success in the Brazilian producing regions, making Brazilian cultivars obsolete (GALVÃO et al., 2017).
Brazil, increasingly, has imported seedlings from Argentina and Chile, raising its dependence on external sources, generating an increase in production costs and delays in planting, which can start only at the end of April, being late for some regions that start their crops in March (ANTUNES; PERES, 2013).Moreover, the entry of these plants in Brazil in large-scale endangers the production by the possibility of introduction of pathogens and pests.The main alternative to reducing dependence on imported cultivars and reducing plant health risks comes from the progress of the Brazilian genetic improvement programs, which are currently stagnant or in slow development.
Genetic improvement has similar characteristics of interest for all breeding programs, but their relative importance is different for breeders as it depends on each region (HANCOCK et al., 2010).
In order to select promising materials, agronomic evaluations of cultivars performance are not enough.In the improvement, the characteristics that are linked to the quality of the fruits are flavor, shape, color, firmness, brightness and more recently the contents of bioactive compounds (vitamins, phenolic compounds, etc.), which is due to the increasing demands of consumers for products that promote health, since scientific studies demonstrate the beneficial effects of its compounds as antioxidant, anti-inflammatory and anticancer power (PINELI et al., 2011).
Strawberry is a fruit that has great nutritional appeal, because it has functional properties, such as antioxidant action, ability to reduce susceptibility to infections, diuretic effect and anti-inflammatory activity.
It is rich in vitamin C and has phenolic compounds.These groups are rarely found in free form, and may be linked to proteins, lipids, terpenoids, hydroxycinnamic acid, carbohydrates and can form ester with organic acids (ROCHA et al., 2008).Phenolic compounds also act as natural antioxidants, have anticarcinogenic activity and lower incidence of cardiovascular diseases (PINELI et al., 2015).
The objective of the study was to perform a postharvest characterization of strawberry hybrids obtained from the commercial cultivars, in order to select materials with superior characteristics to the cultivars planted in Brazil.

Material and methods
The experiment was developed at the State University of the Center-West, UNICENTRO in Guarapuava, PR, (24°14'52" S latitude, 51° 41'06" W longitude and 1,120 m altitude).
The experimental design was a randomized complete block (DBC) with three replicates.The plot consisted of 15 plants of each hybrid (1.5 m) and three replicates.
The spacing used was 0.30 m x 0.40 m forming two lines.The irrigation system adopted was with dripping tubes, spacing 0.30 m between drips.
The plots were covered with black polyethylene film (mulching) with a thickness of 30 uM.Throughout the cycle, the fertilization was performed every 30 days, consisting of 60 kg ha -1 of ammonium sulfate, 11.5 kg ha -1 of potassium sulfate and 14.5 kg ha -1 of potassium chloride.At the beginning of flowering, the plants were sprayed with boric acid and zinc sulfate at the concentration of 1% and 2%, respectively, and in the stage of fruit production with calcium chloride at 0.4% every 15 days.Fertilizations were carried out based on soil chemical analysis and according to the recommendations for the crop.No phytosanitary control was carried out.
The post-harvest characterization of the strawberry fruits involved the following laboratory analyzes, performed in triplicate: determination of soluble solids content (SS), performed in digital refractometer and expressed in ºBrix; determination of the titratable acidity (TA), performed by the titration method of Aldofo Lutz Institute (1985) and expressed as a percentage of citric acid; determination of the ratio, relationship between soluble solids contents and titratable acidity (SS / TA); determination of the levels of vitamin C, performed by the standard titration method of Benassi and Antunes (1988) and expressed as mg of ascorbic acid/100g sample; determination of total phenolic contents by the spectrophotometric method of Woisky and Salatino (1998) and expressed in mg of Gallic acid/100 g sample and determination of anthocyanin contents, performed by the spectrophotometric method of the pH difference of Giusti and Wrolstad (2001) and expressed in mg cyanidin-3-glycoside/100 g sample.
Data were submitted to the normality of the residual variances by the Shapiro-Wilk test, followed by analysis of variance and later the means were grouped by the Scott-Knott test at the 5% level of significance with the aid of the statistical program SISVAR version 5.6.

Results and discussion
The analysis of variance indicated that there was a difference (p <0.05) among the strawberry hybrids for all post-harvest characteristics evaluated.
For the soluble solids (SS) (Table 2), the hybrids presented values ranging from 6.3 to 9.7 ° Brix.Hybrids RVFS 13-24 and RVCS 13-07 were the ones that stood out the most for the characteristic, with a very expressive value (both with 9.7ºBrix), differing from other materials.Comparatively, Camargo et al. (2009) found in the same cultivation region values of 8.1°Brix for Camarosa and 9.3°Brix for Sweet Charlie cultivated in the conventional system, these same cultivars were used at the crossing that originated the hybrids evaluated in the present study, which may indicate the probability of related genes inheritance.Antunes et al. (2010) evaluated six commercial strawberry cultivars in the southern region of Brazil and obtained values of 6.8 to 8.7ºBrix, with an average of 7.90ºBrix, which corroborates the average obtained for the evaluated hybrids.
Regarding the titratable acidity content, the highest value was determined in the RVFS 13-07 hybrid (1.11% citric acid), differing from other materials.The acid values obtained with most hybrids approximate to those found by Camargo et al. (2009) in strawberry fruits grown by the conventional method, 0.90% for Camarosa and 0.91% for Sweet Charlie, which proves that in genetic improvement programs the characteristics of interest can be passed on at crossings.The organic acids present in the fruits influence taste, odor, color, stability and quality maintenance.Antunes et al. (2010) determined an average of 0.72% of acidity in fruits of six strawberry cultivars in RS, a value slightly higher than that determined by the authors.
Considering the SS/TA ratio, which is a determinant of commercial fruit quality, two hybrids stood out, RVFS 13-24 (11.9) and RVCS 13-07 (11.3), both of which differed from the other evaluated hybrids.These values are considered to be very satisfactory because, according to Kader (2002), it is highly recommended to have a minimum of 7% soluble solids, and/or a maximum of 0.80% titratable acidity, i.e. this ratio must be higher than 8.75.The RVFS 13-24 and RVCS 13-07 hybrid ratio values were higher than those found by Camargo et al. (2009) for Sweet Charlie (10.30) and Camarosa (8.96) in the same growing region.
The vitamin C contents of the hybrids were divided into two groups.The first group had fruits ranging from 149.2 (RVCS 13-10) to 182.0 (RVFS 13-07) mg of ascorbic acid 100g -1 and the second group, from 142.4 (RVDA 13-01) to 120.2 (RVFS 13-24) mg of ascorbic acid 100g -1 .According to Lee and Kader (2000), the vitamin C content of strawberry fruits may vary depending on the variety, cropping system, fruit maturation, pre-harvest climatic conditions and postharvest management.Olsson (2004) still reiterates that between cultivars there may be variation in ascorbic acid concentration of two to three times, which can be evidenced by the results obtained in the present study.For the anthocyanins characteristic, the highest pigment content was determined in the RVFS 13-07 hybrid (81.0 mg of cyanidin-3-glycoside 100g -1 sample), which differed from the other evaluated materials.The anthocyanin content may present as a criterion for choosing cultivars because of the health benefits.Musa (2016), in RS, found close values when comparing anthocyanin levels of cultivar Festival and San Andreas.In the conventional system, cv.Festival averaged 46.91 mg 100g -1 and San Andreas 41.18mg 100g -1 .Already, Calvete et al. (2008) and Antunes et al (2010), also in RS, obtained anthocyanin values ranging from 21 to 56 mg 100g -1 for eight cultivars and 22.44 to 38.01 mg 100mL -1 for six cultivars, respectively.Comparatively, anthocyanins values determined in this study were higher than that found by other authors, as reported above, this may have been influenced by weather factors such as temperature and lighting (TEIXEIRA et al., 2008) or by genetic factors influencing the content of secondary compounds in fruits, in the case of strawberry, the differences among the various cultivars that are produced around the world have been extensively reported (VIZZOTTO, 2012).
The phenolic content of the hybrids fruits evaluated in the present study ranged from 175.9 (RVOT 13-22) to 197.6 (RVCA 13-08) mg of gallic acid 100g - 1 .Rocha et al. (2008) determined the phenolic content in three strawberry cultivars (Aroma, Toyorrinho and Oso Grande) in the region of Lavras/MG and found, respectively, values of 202.87; 217.14 and 222.85 mg of tannic acid 100 g -1 of pulp, higher than those found with hybrids in the Guarapuava region.There are many factors that can influence the phytochemical content in fruits and one of them is the stage of development, the total phenolic compounds content has a decrease from 80 to 90% from the stage where the fruit is green to when it is white and then, maintains this constant value until the end of fruit development.When assessing the effect of different levels of fertilization, using as basis the recommendation of the Chemical and Soil Fertility Commission (SBCS, 2004), the content of phenolic compounds in strawberries has been observed that when the recommended fertilizer level is used or this one plus 50%, the levels of phenolic compounds and antioxidant activity were higher than the other treatments in the Camarosa cultivar, which was not observed in the Festival cultivar, showing that the cultivar factor is very important for the decision of the technologies that will be used, aiming at fruit quality (VIZZOTTO, 2012).

Conclusion
The results obtained here demonstrate that the use of the parents can result in good progenies, however these results are dependent on the combination, since in some crossing, in which these cultivars participated as one of the parents, the results were not so promising.
The characterization of strawberry hybrids in the Guarapuava/PR region indicated that RVFS 13-07, RVFS 13-24, RVCS 13-07, RVCS 13-10 and RVCA 13-08 materials stood out in the post-harvest evaluation, with higher levels of functional compounds (vitamin C, anthocyanins and phenolics) and higher values of quality parameters (soluble solids, titratable acidity and ratio), important characteristics either for the in natura consumption or for by the industry use.These hybrids proved promising to continue the crop genetic improvement program by demonstrating that they carried characteristics of interest at the crossing.
The values obtained for the analyzed characteristics were higher than the values found in the literature for the most planted and consumed cultivars in Brazil and in the world, which demonstrates the efficiency in the selection process.

Table 1 .
Strawberry hybrids resulting of crossing among commercial cultivars.

Table 2 .
Average of soluble solids (SS), titratable acidity (TA), ratio (SS/TA), vitamin C, anthocyanins and phenolics of fruits of 15 strawberry hybrids obtained by crossing of commercial cultivars.Means followed by the same letter in the column did not differ by the Scott-Knott test (p <0.05). *