Abstract
During the last few years, the nutritional value of fruit has been widely studied and requested by the consumers, especially for the general health benefits it can provide. In this study, offsprings from inter- and intra-specific strawberry cross combinations were studied with the aim to evaluate and identify new genotypes that can show the best compromise between sensorial and nutritional quality. Seventy-eight strawberry offsprings selection, originating from eight Fragaria spp. inter- and intra-specific crosses, were screened to study the role of the genetic origin of the parents in segregating new genotypes with an improved sensorial and nutritional quality of the fruit.
INTRODUCTION
A greater consumption of fruit and vegetables is considered as one way of increasing the intake of antioxidants, and the strawberry, like other berries, represents one of the most important sources of bioactive compounds with antioxidant activity (CitationBattino et al., 2009; CitationProteggente et al., 2002). Accordingly, the increase of consumption of berries richer in “healthy compounds” is seen as an appropriate strategy for improving human health.
Increase of the antioxidant levels in fruit through breeding and/or biotech is an important option to support a higher antioxidant intake even when the consumption of fruit is low. If nutritional components are also combined with a high standard sensorial fruit quality the perspective of consumer health can be further improved by the increased consumption; this can be the case of strawberry fruit (CitationTulipani et al., 2009).
An increased level of antioxidants in fruit through breeding and/or biotechnology is an important option to support a higher antioxidant intake even when the consumption of fruit is low. If nutritional components are also combined with high standard sensorial fruit quality the perspective of consumer health can be further improved by the increased consumption. The effect of genotypes in affecting the nutritional quality of strawberry is well known (CitationAzodanlou et al., 2003; CitationOlsson et al., 2004; CitationScalzo et al., 2005; CitationWang et al., 2002), however, the antioxidants and antioxidant capacity in strawberry extracts from whole fruits vary considerably among genotypes (CitationScalzo et al., 2005; CitationShiow et al., 2007; CitationWang and Lewers, 2007). Furthermore, the available information for improving strawberry nutritional traits by breeding is limited (CitationCapocasa et al., 2008, Citation2009; CitationDiamanti et al., 2010). Accessions of the progenitor wild species are valued by strawberry breeders as sources of novel traits, especially pest resistance and abiotic stress tolerance (CitationHancock et al., 2002). Furthermore, previous investigations (CitationCapocasa et al., 2008, Citation2009; CitationShiow et al., 2007; CitationTulipani et al., 2008) have shown improvement in fruit nutritional quality in breeding material originated from Fragaria virginiana spp. glauca (FVG) inter-specific crosses.
In this work, strawberry sensory (soluble solids, total acidity, firmness, and color) and nutritional (total antioxidant capacity, polyphenols, and anthocyanin) attributes were used for screening new genetic material derived from a breeding program including families originated from intra-specific and inter-specific backcross combination performed with parents selected for their highest nutritional quality.
MATERIALS AND METHODS
Strawberry fruit genetic variability originated by 8 different strawberry intra- and inter-specific cross combinations, was explored by analyzing 78 selections obtained from the following cross-combinations: 2 from intra-specific cross (F. × ananassa) combinations between commercial cultivar and advanced selection of F. × ananassa; 3 F2 back-crossing using the F1 selection AN94,414,52, F. × ananassa (Don) × F. virginiana glauca (FVG22); and 3 F3 back-crossing using AN00,239,55 as common progenitor, an F2 selection derived from the back crossing of selection F1 AN94,414,52 with 91,143,5 (F. × ananassa advanced selection) (). During one season (2010), the 78 selections, plot of 6 plants each, from the 8 families (from 8 to 11 seedlings for each family) were grown in open field conditions, together with the parents, at the P. Rosati University Experimental Farm in Agugliano (Ancona), Italy, using the plastic hill culture production system. Fruits were hand harvested at the ripe stage; sorted to eliminate damaged, shriveled, and unripe fruit; and selected for uniform size and color.
TABLE 1 List of Families and Corresponding Progenitor and Number of Offspring Taken into Account for the Study of Fruit Nutritional Quality
Fruit Sensory Quality
Selections and parents sensory parameters were analyzed on commercial fruit in the harvesting day at each harvest (2nd, 3rd, 4th), by analyzing for total soluble solids content (TSS), titratable acidity (TA), fruit chroma index and lightness (L*), and fruit firmness. Quality parameters were analyzed following the method described by CitationCapocasa et al. (2008).
Fruit Nutritional Quality
Nutritional parameters of selections and parents were studied on undamaged fruit samples (300–600 g), including pooled fruit of the 2nd, 3rd, and 4th harvests. These fruit samples were collected for each replicate of the parents and from single selections, and frozen at –20°C under reduced-light condition until extraction. Frozen fruit samples were homogenized (with a T25 Ultraturrax blender, YKA labortecknik, Staufen, Germany) with solvent solution (ethanol/water, 80:20 v/v) and extracts were utilized to assay the nutritional bioactive with the following methods: Total antioxidant capacity (TAC): TEAC (Trolox equivalent antioxidant capacity) assay, was applied according to CitationRe et al. (1999) to study the antioxidant activity of the strawberry. After the addition of 1.0 ml of ABTS• + working solution (A734 nm = 0.700 ± 0.02) to 10 μl of Trolox standards (0–1.5 mM), or extracts, the absorbance was read exactly 1 min after initial mixing. The final result was expressed as Trolox Equivalents (μmoles/g fresh weight (FW). Total phenol content (TPH): Folin-Ciocalteu assay was performed according to CitationSlinkard and Singleton (1977) to study strawberry TPH. Fruit extracts were quantified by comparison of a standard curve of gallic acid and final results were expressed as gallic acid equivalent (GAE mg/g FW). Anthocyanin content (ACY) was measured by the pH differential shift method (CitationGiusti and Wrolstad, 2001). The assay was performed using the anthocyanin characteristic to change intensity of hue depending on pH shifting. Briefly, the samples were diluted to a ratio of 1:10 with potassium-chloride (pH 1.00) and with sodium acetate (pH 4.50) and the corresponding maximum absorbance for both solutions was measured (respectively at λ = 500 nm, approximately and λ = 700 nm).
Strawberry plant production was also evaluated in single plot of all selections, at each harvest, by evaluating the following parameters: Total Production: evaluated weighing the plant whole production. Commercial Production: evaluated weighing whole fruits with diameter Ø ≥ 0.22 mm, full ripe, which does not show injuries. Fruit Weight: calculated on the average weight of 20 commercial fruits from each harvest. Undersized fruit: evaluated weighing whole fruits with diameter Ø ≤ 0.22 mm, full ripe, which does not show injuries. Misshapen Fruit: evaluated weighing fruits with not regular form. Rot Fruit: evaluated counting the rot fruits and then multiply for the average fruit weight.
In the 2010 harvesting season, fruit sensorial (SS, TA, firmness, chroma, L*) and nutritional (TAC, TPH, ACY) quality were analyzed in triplicate for each selection identified in 2009 and for their corresponding parents. All data were submitted to one-way analysis of variance, ANOVA test, for mean comparisons. The ANOVA was performed for single cross combinations as random effect. Data on fruit sensorial and nutritional parameters are reported as means ± standard error (SE). The differences were calculated according to the SNK test and were considered significant at p ≤ 0.05. Correlations among sensorial (SS, TA, Firmness, Chroma, L*) and nutritional parameters (TAC, TPH, ACY) were analyzed using Pearson's correlations.
RESULTS AND DISCUSSION
Fruit sensory quality of FVG × FxA F2, F3 cross combinations resulted in increased values in TSS. Backcrosses of F2 AN07005 and F3 AN07215 backcrosses showed the highest values, followed by the other backcross combinations. FxA cross combinations resulted in lower TSS values, in particular selection AN07009 (). Marked differences in TA were observed among the backcrosses. In particular, F3 backcrosses AN07,215, AN07,216, and F2 AN07,004 showed the highest values for TA, whereas FxA crosses showed the lowest values (). The increased TSS in FVG backcrosses was not associated with a decrease in fruit acidity, causing an increased sweetness in the fruit generated by inter-specific backcrosses.
TABLE 2 Fruit Sensory and Nutritional Parameters of Selections from F2, F3 Backcross and Intra-Specific Cross Populations, Evaluated in 2010. Results Are Presented as Means Values and Standard Errors (SE) of Offspring Selections for Each Family
The results on fruit firmness showed that fruit of F2 and F3 inter-specific crosses were less firm than those from the selections generated by intra-specific cross combinations. The highest firmness values were measured in the fruit of AN07009 followed by AN07007 family (). The lowest fruit firmness values were observed in the fruit from FVG backcrosses F2 AN07,004 and F3 AN07215. These findings demonstrated that the genetic influence of wild genotype on its backcrosses progenies (CitationFigueroa et al., 2008) influenced negatively the quality of strawberry fruit. Rapid softening alters the texture and shortens postharvest life and quality (CitationPerkins-Veazie, 1995).
Analysis of fruits' colorimetric parameters revealed that fruits from intra-specific cross combination showed dark and pale fruits in the AN07,007 family (), which showed the highest values among all the families, while inter-specific cross combinations generated progenies with higher values of L* as already observed for Rubus wild species (CitationÇekiç and Özgen, 2010).
Fruit nutritional parameters evaluated on the selections generated from inter-specific backcross and intra-specific cross combinations showed marked differences in particular for fruit TAC and ACY. The fruit of F3 and F2 cross combinations contained higher values for TAC, above all F3 AN07,215 family and twice the value of TAC measured among fruit of intra-specific cross combinations (). The TAC values found among the fruit from F3 AN07006 and F2 AN07004 families were also higher than that of intra-specific cross combinations. Both inter-specific cross combinations, F2 and F3, which involve the cultivar Clery as common male parent, showed TAC values similar or closer to the ones found for intra-specific cross combinations ().
FTC did not show marked differences among cross combinations, as observed for fruit TAC F3 AN07,215 and F2 AN07,004 emerges in respect to the other families because of their high values of TPH, while the other cross combination, either intra- and inter-specific did not show great variability of such nutritional parameters (). Fruit ACY content confirmed the differences of nutritional quality observed among inter-specific backcrosses and intra-specific crosses; in fact, in all the fruit of F2 and F3 back crosses selections were found similar fruit ACY values, but among them emerges the F3 AN07,216 family with the highest value, followed by F2 backcrosses AN07,003, while even for fruit ACY content the lowest value is observed in intra-specific AN07,009 family (). Such results confirm the importance of wild genotype as a genetic resource for the improvement of fruit nutritional quality as already observed by CitationScalzo et al. (2005), CitationÇekiç. and Özgen (2010), CitationCapocasa et al. (2008), and CitationDiamanti et al. (2010).
The evaluation of the productive parameter among selection revealed that inter-specific crosses, either F2 than F3, have a fruit weight that did not fulfill the standard required by the market; in fact, for F3 and F2 backcrosses, the average fruit weight did not reach the 15 g per fruit while intra-specific crosses showed values closer to the standard required by the market (). Furthermore, F3 and F2 backcrosses also showed high production of undersized fruit, which negatively influence the total production creating a further negative productive parameter for inter-specific backcross combinations, while intra-specific cross combinations showed a lower production of undersized fruit in comparison to the results observed in F2 and F3 backcrosses. Nevertheless, such negative productive parameters, inter-specific backcrosses showed a lower production of rot fruit per plant either for F2 than for F3 backcrosses, while intra-specific cross combinations showed a higher production of such parameters (). These results confirm the high importance of wild species as a genetic source for disease resistance as already observed by CitationHancock and coworkers (2002).
Results of Pearson's correlation for sensorial and nutritional parameters for F2, F3, and FxA crosses resulted in a different level of correlation (). The anthocyanin content results in strongly negatively correlated chroma index and luminosity, indicating that the intensity of the color is indirectly proportional to the anthocyanin content, or that darker and paler fruits possess lower ACY. In addition, a negative correlation was found within fruit firmness and TA and within firmness and fruit total antioxidant capacity, also negative correlation resulted within luminosity and solid soluble content.
The high values of negative correlation within sensorial and nutritional parameters are also associated to high positive correlations, in particular, within fruit antioxidant capacity and solid soluble, and within fruit TAC and TA. Fruit total antioxidant capacity also shows strong positive correlation within both nutritional parameters, fruit total phenol content and anthocyanin content, which confirms the antioxidant action developed by such bioactive compounds, in particular, TPH that showed the highest value of positive correlation. As for nutritional parameters also within sensorial parameters were found high positive correlation value, in particular within TSS and TA, as predictable by the results observed from the sensorial parameters of each family (). Furthermore, lower positive correlation values observed within solid soluble and phenol contents, within SS and anthocyanin contents, and also within TPH and anthocyanin contents ().
TABLE 3 Plant Production Parameters of Selections from F2, F3 Backcross and Intra-Specific Cross Populations, Evaluated in 2010. Results as Means Values and Standard Errors (SE) of Offspring Selections for Each Family
TABLE 4 Pearson's Correlation Matrix of Fruit Sensorial and Nutritional Parameters of Selections from Inter-Specific and Intra-Specific Cross Populations
CONCLUSION
The evaluation carried out on the genetic pool originated by the breeding program developed by the Faculty of Agriculture of “Università Politecnica delle Marche,” which included F. virginiana spp. glauca inter-specific backcross and F. × ananassa intra-specific cross. The findings confirmed that fruit nutritional quality (TAC, TPH, ACY) and sensory quality (SS, TA, chroma, L*, Firmness) are higher in offspring populations originating from FVG inter-specific back-cross in respect to the F. × ananassa intra-specific cross.
The results obtained in this work showed that the use of the wild genotype of F. virginiana spp. glauca in inter-specific crossing and its consequential back crossing gives useful improvement in fruit nutritional and sensory qualities. Improvements in these traits can be achieved also by programming F. × ananassa intra-specific crosses and allowing the production of progenies with productivity traits more similar to those of the commercial cultivars. While the use of wild backcross reduced the number of offspring that have commercial productivity traits, the breeding strategy increased fruit nutritional and sensory qualities and increased fruit disease resistance. Phenol and anthocyanin contents are strictly positively correlated to fruit total antioxidant capacity whereas ACY was negatively correlated with chroma index and fruit lightness (L*). The two types of combination programs (inter-specific backcrosses and intra-specific crosses) can be used for the improvement of strawberry nutritional quality, but the success of the program is strictly related to the combining heritability of the different parents.
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