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Influence of different rootstocks on yield precocity and fruit quality of ‘Tarocco Scirè’ pigmented sweet orange
Scientia Horticulturae 230 (2018) 62–67
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Influence of different rootstocks on yield precocity and fruit quality of ‘Tarocco Scirè’ pigmented sweet orange
T
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A. Continellaa, C. Pannitteria, S. La Malfaa, , P. Leguab, G. Distefanoa, E. Nicolosia, A. Gentilea a
Department of Agriculture, Food and Environment, University of Catania, Via Valdisavoia, 5, 95123 Catania, Italy Plant Sciences and Microbiology Department, Miguel Hernández University, Research Group in Plant Production and Technology, Ctra. de Beniel, km 3,2. 03312 Orihuela, Alicante, Spain b
A R T I C L E I N F O
A B S T R A C T
Keywords: Anthocyanins Blood orange Citrus Scion/rootstock combination Trifoliate orange hybrids
Several studies in citrus-producing countries are currently being carried out to select and evaluate rootstocks that are tolerant to Citrus Tristeza Virus (CTV) and can be adopted in different citrus production areas. An evaluation of rootstock suitability must consider the productive and qualitative features as well as the adaptability to varied environmental conditions (i.e., soil characteristics). Additionally, some varieties present qualitative aspects that are appreciated by consumers but can be affected by the use of different rootstocks. In Italy, the qualitative traits of pigmented or blood oranges, which are characterized by the presence of anthocyanins in the peel and flesh, are strongly influenced by several factors, including the scion/rootstock combination. The objective of this study was to evaluate and compare the influence of ten rootstocks on yield precocity and fruit quality of ‘Tarocco Scirè’ pigmented sweet orange in a Sicilian area within the Protected Geographical Indication (GPI) “Arancia Rossa di Sicilia” production district. Five of the ten rootstocks, namely, ‘Bitters’, ‘Carpenter’, ‘Furr’, ‘F6P12®’ and ‘F6P13′, have recently been released and produced good yields in limiting soil conditions. In this study, the important role of rootstock in determining the organoleptic quality, specifically the sugar content, and the anthocyanin concentrations in both the pulp and the juice was demonstrated. Some of the rootstocks that were recently introduced in Italy, i.e., ‘Bitters’ and ‘Furr’, were promising because they positively influenced several agronomic and qualitative parameters in the tested conditions, positively affected the yield precocity and enhanced the fruit juice anthocyanin content. Overall, these results contribute to the assessment of the role of different rootstocks in the post-CTV Italian citrus industry.
1. Introduction The use of rootstocks in fruit tree crops is important for plant performance and yield quality. For decades, sour orange (Citrus aurantium L.) has been widely used in the Mediterranean citrus industry because it was considered the most suitable rootstock in several citrus-growing areas for its good productivity in different environmental and pedological conditions, including calcareous soils. Its tolerance to many fungal diseases, such as Phytophthora spp., and to viroids, such as exocortis (CEVd) and xyloporosis (CCaVd), is an important element that brought sour orange into wider use. However, its intolerance to Citrus Tristeza Virus (CTV) impedes its use in new plantings of orange and mandarin orchards due to the diffusion of the virus (Moreno et al., 2008). To overcome this problem, citranges [Citrus sinensis (L.) Osb x Poncirus trifoliata (L.) Raf.] and other intergeneric hybrids (i.e., ‘Swingle’ citrumelo) tolerant to CTV have been used. However, the search for alternative rootstocks and their evaluation with different scion
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combinations and in various environmental conditions are still important goals to achieve in citrus-producing countries (Louzada et al., 2008; Reforgiato Recupero et al., 2009; Legua et al., 2014; Fu et al., 2016). Recently, research institutions from several countries have released new promising rootstocks; among these, the ‘Bitters’, ‘Carpenter’ and ‘Furr’ intergeneric hybrids [C. sunki Hort. ex Tan. x P. trifoliata (L.) Raf.] were released by the University of California, Riverside (UCR) (Federici et al., 2009) and are reported to be tolerant to calcareous soil and to produce good yields. Similarly, from the breeding program started in 1968 at CREA, Acireale, Italy, the rootstocks ‘F6P12®’ and ‘F6P13′ [C. latipes x P. trifoliata (L.) Raf.] have been selected for their good vegetative and productive performance (Reforgiato Recupero et al., 2009). Italy holds the 11th place in terms of world citrus production, with approximately 2.7 million tons (FAOSTAT, 2014), and half of the Italian cultivation area is in Sicily. In this region, sweet orange [Citrus sinensis (L.) Osbeck] cultivation represents 70% of the pigmented
Corresponding author. E-mail address: [email protected] (S. La Malfa).
https://doi.org/10.1016/j.scienta.2017.11.006 Received 1 August 2017; Received in revised form 27 October 2017; Accepted 1 November 2017 Available online 20 November 2017 0304-4238/ © 2017 Elsevier B.V. All rights reserved.
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cultivars (the so-called “blood oranges”). Catania Plain, at the foothills of Etna Volcano, is the most suitable production area for anthocyanin biosynthesis (La Rosa, 2012) and is within the Protected Geographical Indication (GPI) “Arancia Rossa di Sicilia” production district. Among the Italian blood oranges, ‘Tarocco’, with its several clones (including ‘Tarocco Scirè’, as used in the present study), is most famous for its greater peelability, taste and nutraceutical properties compared to blonde oranges, which are determined by the presence of anthocyanins and are responsible for their attractive red brilliant color (Lo Piero, 2015). ‘Moro’, which is deeper in color, is the second most widely cultivated pigmented variety in Italy. Specific environmental conditions, such as marked night/day thermal excursions, are considered to play an important role in pigment biosynthesis and its accumulation in fruits of selected genotypes (Rapisarda and Giuffrida, 1994; De PascualTeresa and Sanchez-Ballesta, 2008; Butelli et al., 2012), thus improving nutritional value and consumer acceptance. The anthocyanin contents in blood oranges, particularly in ‘Tarocco’ clones grafted onto sour orange, have been investigated extensively (Maccarone et al., 1998; Rapisarda and Russo, 2003; Fallico et al., 2017), primarily for their health value (Dugo et al., 2003; Proteggente et al., 2003; Grosso et al., 2013), but little has been reported on the effect of rootstocks on the qualitative parameters of blood oranges (Incesu et al., 2013). Since pigmented varieties are currently high-value products for the Italian citrus industry, it is important to select for these cultivars the most suitable rootstocks for different pedoclimatic conditions. In this work, we evaluated the influence of several CTV-resistant rootstocks on the yield precocity and fruit quality of a pigmented sweet orange line, namely, ‘Tarocco Scirè’, in an environment suitable for the cultivation of blood oranges.
2014. The number of harvested fruits, total production per tree and mean fruit weight were determined. The yield efficiency index for 2016/2017 was calculated as the ratio of yield to canopy volume and expressed as kg/m3. 2.3. Morphological and physicochemical parameters determination Starting in season 2015/2016 harvest, fifty representative pooled fruits from each rootstock combination were selected, individually weighed, measured and then used for juice extraction. Fruit height, equatorial diameter and rind thickness (mm) were measured using an electronic digital slide gauge (model CD-15 DC; Mitutoyo (UK) Ltd, Telford, UK) to within 0.01 mm accuracy. Peel color was recorded on two opposite points of the equatorial region for each fruit using a Minolta CR-400 chroma-meter (Minolta Corp., Osaka, Japan) according to the methodology described by Pannitteri et al. (2017). The results were expressed as a citrus color index (CCI = a*1000/L*b), where a* indicates chromaticity on a green (−) to red (+) axis and b* indicates chromaticity on a blue (−) to yellow (+) axis; this index is widely used in the citrus industry as a maturation index (DOGV, 2006). Fruit juice was extracted with a commercial juice extractor (Kenwood Citrus Juicer JE290, UK). Three juice samples, from the pooled juice of six fruits from 3 replicates per rootstock combinations, were used for chemical analyses. Juice was weighed and expressed as a percentage of the total fruit weight. The Total Solid Soluble (TSS) content was determined using a digital refractometer (Atago CO., LTD, model PR-32 α, Tokyo, Japan), with the results expressed as °Brix. Titratable acidity (TA) was determined by potentiometric titration (Hach, TitraLab AT1000 Series) of the juice with 0.1 N NaOH beyond pH 8.1 according to the AOAC method (AOAC, 1995), with the results expressed as g L−1 of citric acid equivalent. Ripening index (RI) was calculated as the ratio between TSS and TA. Vitamin C (L-ascorbic acid) was determined using an automatic titration apparatus (702 SM Titrino, Metrohm, Herisau, Switzerland) with 0.001 M I2, and the results were expressed as mg L−1. Total anthocyanin content (TAC) was determined spectrophotometrically by the pH differential method (Fuleki and Francis, 1968), where the absorbance was measured using a spectrophotometer (NanoDrop 2000, Thermo Scientific) at 510 and 700 nm in buffers at pH 1.0 and 4.5. The results were expressed as the mg of cyanidin-3glucoside equivalents per liter of fresh weight.
2. Materials and methods 2.1. Plant material Ten rootstocks, ‘Troyer’, ‘Carrizo’ citrange, ‘C35′ [C. sinensis (L.) Osb. cv. ‘Ruby’ x P. trifoliata (L.) Raf.], ‘Swingle’ citrumelo [C. paradisi (Macfadyen) x P. trifoliata (L.) Raf.], ‘Bitters’, ‘Carpenter’, ‘Furr’, ® ‘F6P12 ’, ‘F6P13′ and ‘Severinia’ [Severinia buxifolia (Poir.) Ten.], were evaluated in combination with ‘Tarocco Scirè’, a virus free selection obtained by micro-grafting a scion. Some of the selected rootstocks have been recently released, and others are already widely used in citrus producing areas. Rootstocks were propagated from seeds and plants were T-budded in the nursery with ‘Tarocco Scirè’, a medium-ripening line of blood oranges. This line was chosen to better evaluate the effect of rootstock on fruit pigmentation because this line is characterized by a rather low content of anthocyanins in the fruit (Caruso et al., 2016). After one year, budded plants were transplanted. The experimental field was established in 2010 in Catania Plain (37°17′04′’N, 14°53′16′’E). The experimental design was a complete randomized block, with five plots of 20 trees and each tree spaced 5 m x 3 m apart. The texture components of the soil were 68.6% sand, 23.6% loam, and 7.8% clay. In the experimental field, the pH values were 8.5, and the content of active lime was 3.0%. The orchard was subjected to standard cultural practices.
2.4. Statistical analysis Statistical analyses were performed using STATISTICA 6.0 (Statsoft Inc., Tulsa, OK) and used to test the significance of each variable (P ≤ 0.05). A basic descriptive statistical analysis was followed by an analysis of variance test for mean comparisons. The method used to discriminate among the means (Multiple Range Test) was Fisher’s Least Significant Difference (LSD) procedure at a 95.0% confidence level. 3. Results and discussion 3.1. Vegetative and yield determinations The different rootstocks significantly affected several growth parameters of ‘Tarocco Scirè’ (Fig. 1). The canopy volume, as measured in November 2016, was larger in plants budded on ‘Furr,’ ‘Carpenter’ and ‘C35′ (10.1, 9.5 and 9.4 m3, respectively). The smallest canopy volume was observed in combination with ‘Troyer’ citrange (4.7 m3). The TCSA values ranged from 139 cm2 (for ‘Swingle’ citrumelo) to 75 cm2 (for ‘Bitters’ and ‘Troyer’citrange) and were not always correlated with the canopy volume; for instance, ‘Carpenter’ and ‘C35′ exhibited a high canopy volume but reduced TCSA. Among the rootstock released by UCR, ‘Bitters’ was less vigorous (i.e., it was smaller and had shorter branches) than were ‘Carpenter’ and ‘Furr,’ as observed by other
2.2. Vegetative and yield determinations The trunk circumference (10 cm above the bud union) and canopy volume were measured annually for 6 years from 2010 through 2016. Trunk cross sectional area (TCSA) was calculated by the equation: TCSA = π ( diameter )2. The tree volume was calculated by the equation: 2 V = 0.524 x height x width2 because the tree shape was assumed to be one-half of a prolate spheroid (Morse and Robertson, 1987). Yield was recorded beginning with the first harvest, which occurred in 2013/ 63
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Fig. 1. Canopy volume and trunk cross sectional area (TCSA) recorded for ‘Tarocco Scirè’ on different rootstocks in 2016.
respectively) but were less productive during the first three years, resulting in lower cumulative yields. ‘F6P13′ and ‘Severinia’ showed the lowest yield: the former produced significantly only in 2016/2017, with an average yield of 13.4 kg/tree. In contrast, trees in combination with ‘Severinia’ only produced in the first year of production because all the plants grafted with this rootstock died in the second year. Our hypothesis is that this negative performance was due to the very high sensitivity of this rootstock to active lime. In the sixth year of observation, the highest values of yield efficiency (Fig. 3) were registered for ‘Bitters’ (8.1 kg/m3), followed by ‘Carpenter’, ‘C35′ and ‘Furr’ (7.5, 7.1 and 7.1 kg/m3, respectively). ‘Swingle’ citrumelo and ‘F6P13′ were the rootstocks with the lowest yield efficiency (3.0 and 2.8 kg/m3, respectively).
authors (Siebert et al., 2010). This result appears to be interesting in the context of citrus rootstocks, as only a few are considered capable of limiting vegetative growth and giving good yields. The only rootstock that resulted in dwarfing in the citrus was the ‘Flying Dragon’ trifoliate orange (Roose, 1986). More recently, two hybrids, namely, FA-517 [Citrus nobilis Lour × Poncirus trifoliata L. (Raf.)] and FA-418 [Troyer citrange × C. deliciosa (Ten)] presented dwarfing properties in scions (Forner-Giner et al., 2014). Among citrus rootstocks, ‘Swingle’ citrumelo has generally been considered vigorous (Wutscher, 1974). In our study conditions, the canopy volume of this rootstock was lower than those of ‘Furr’, ‘Carpenter’ and ‘C35′. For citranges, ‘Troyer’ showed the lowest values of both the vegetative parameters, whereas ‘Carrizo’ presented intermediate values. ‘Severinia’ data are not reported because all the plants grafted from this rootstock died by the second year. Fruit production started in the third year for all rootstocks except ‘F6P13′, which started to produce fruit in the fourth year. In the fourth year of production, the highest cumulative yields were obtained for ‘C35′ and ‘Bitters’ (Fig. 2). ‘Furr’ and ‘Carpenter’ produced more than ‘Bitters’ and ‘C35′ did in the fourth year (70 and 71 kg vs. 57 and 66 kg,
3.2. Morphological and physicochemical parameters determination The highest fruit weights were recorded for trees grafted from ‘Carrizo’ (218 g), ‘C35′ (218 g) and ‘Bitters’ (212 g), which was significantly different from trees grafted from ‘Swingle’ citrumelo, which Fig. 2. Cumulative yield recorded on ‘Tarocco Scirè’ on different rootstocks.
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Fig. 3. Yield efficiency of ‘Tarocco Scirè’ on different rootstocks in 2016/2017.
Table 1 Fruit physical parameters (average of two years 2015/2016 and 2016/2017) of ‘Tarocco Scirè’ sweet oranges grafted on the studied rootstocks.a,b
‘Carrizo’ ‘Troyer’ ‘C35′ ‘Citrumelo’ ‘Bitters’ ‘Carpenter’ ‘Furr’ ‘F6P12′
Fruit weight (g)
Fruit height (mm)
Fruit diameter (mm)
Rind thickness (mm)
Citrus color index
218 201 218 170 212 195 200 204
69.9 65.8 69.1 61.5 66.5 82.7 79.9 74.4
68.6 65.1 67.9 61.8 65.6 80.0 77.4 73.0
4.5 4.4 4.6 4.0 4.2 4.5 4.4 4.2
6.6 ± 1.5abc 6.8 ± 1.5abc 6.5 ± 1.5bc 5.5 ± 2.9d 7.1 ± 2.2ab 7.2 ± 1.5a 7.2 ± 1.6a 6.2d ± 1.5c
± ± ± ± ± ± ± ±
6a* 4a 3a 4b 4a 4ab 3a 4a
± ± ± ± ± ± ± ±
22.1bc 18.6bc 20.9bc 18.1c 18.5bc 11.5a 6.4a 14.5ab
± ± ± ± ± ± ± ±
19.7bc 17.9bc 18.9bc 18.3c 18.2bc 10.0a 5.3a 13.9ab
± ± ± ± ± ± ± ±
1.2a 1.5a 1.4a 1.3a 1.2a 1.1a 1.5a 1.5a
*Values along columns with different letters are different for p ≤ 0.05. a No data are reported for F6P13 since no production was recorded in 2015/16. b No data are reported for ‘Severinia’ because all the plants died in the second year.
Fruits from trees on ‘Carrizo’ citrange and ‘Bitters’ showed the highest TSS values (11.1°Brix), but these values were not significantly different from those of ‘Troyer’ citrange and ‘Furr’, and ‘Swingle’ citrumelo, ‘Carpenter’ and ‘F6P12′ showed the lowest values (9.7, 9.8 and 9.9°Brix, respectively). Rootstocks also significantly influenced TA accumulation in the fruits. The highest TA content was found in fruits from trees on ‘Furr’ (9.7 g citric acid L−1), and the lowest was found in fruits from trees on ‘Carpenter’ (7.8 g citric acid L−1). Conversely, other studies found that the effects of rootstock on fruit juice acidity were non-significant. These results were found in fruits of ‘Lane Late’ trees in combination with C. macrophylla, C. volkameriana and Cleopatra mandarin (Legua et al., 2011b) and in ‘Clemenules’ mandarin grafted on Cleopatra mandarin
had the lowest fruit weight (170 g) (Table 1). Fruit from ‘Swingle’ trees also had the lowest height and fruit diameter. The largest fruit diameters were measured for ‘Carpenter’, ‘Furr’ and ‘F6P12′ (80.0, 77.4 and 73.0 mm, respectively). No significant differences were recorded for rind thickness, which ranged from 4.0 mm for ‘Swingle’ citrumelo fruit to 4.6 mm for fruit grafted from C35 trees. The Citrus Color Index showed the highest values on fruits of plants grafted onto ‘Carpenter’, ‘Furr’ and ‘Bitters’, whereas a paler red color was observed on ‘Tarocco Scirè’ fruits in combination with ‘Swingle’ citrumelo (Table 1). TSS and TA are the most relevant parameters for orange juice quality determination. In this work, we observed significant differences in these two parameters among trees on different rootstocks (Table 2).
Table 2 Fruit qualitative parameters (average of two years 2015/2016 and 2016/2017) of ‘Tarocco Scirè’ sweet oranges grafted on the studied rootstocks.a,b
‘Carrizo’ ‘Troyer’ ‘C35′ ‘Citrumelo’ ‘Bitters’ ‘Carpenter’ ‘Furr’ ‘F6P12′
TSS (°Brix)
TA (g L−1)
RI (TSS/TA)
Juice (%)
Vitamin C (mg L−1)
11.1 ± 0.5a* 10.9 ± 0.2ab 10.2 ± 0.8bc 9.7 ± 0.4c 11.1 ± 0.8a 9.8 ± 0.9c 10.4 ± 0.3abc 9.9 ± 1.2c
8.5 8.8 8.7 9.3 8.0 7.8 9.7 8.9
11.6 12.4 11.8 10.5 13.9 12.6 10.8 11.1
51.6 49.5 47.9 50.7 51.9 48.8 47.7 45.8
655 664 666 677 713 659 668 720
± ± ± ± ± ± ± ±
0.7bcd 0.6abc 0.6bcd 0.7ab 0.6 cd 0.7d 1.0a 1.1ab
*Values along columns with different letters are different for p ≤ 0.05. a No data are reported for F6P13 since no production was recorded in 2015/16. b No data are reported for ‘Severinia’ because all the plants died in the second year.
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± ± ± ± ± ± ± ±
1.5ab 0.9bc 1.0 cd 1.1d 1.3a 1.1bc 1.0d 0.7d
± ± ± ± ± ± ± ±
5.8a 6.3ab 4.0ab 2.6ab 3.5a 5.0ab 3.2ab 0.8b
± ± ± ± ± ± ± ±
73a 22a 103a 64a 69a 58a 61a 69a
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pigmentation levels, there were more hours with temperatures below 6 °C (293 vs. 454, respectively). This result is consistent with the findings of several authors, who noted the role of cold temperatures in enhancing anthocyanin biosynthesis in blood oranges during post-harvest treatments (Crifò et al., 2012; Pannitteri et al., 2017).
and Carrizo citrange (García-Sánchez et al., 2006). The TSS/TA ratio is an important qualitative parameter of Citrus fruits and is the most widely used method for estimating the citrus maturity level (Legua et al., 2011a). The fruits of trees on ‘Bitters’ showed the highest ripening index (13.9), whereas ‘Swingle’ citrumelo had the lowest index (10.5), although these values were not significantly different from those of ‘F6P12′ and ‘Furr.’ Significant differences were found for juice content in the fruit: its percentage ranged from 52% for fruit from trees on ‘Bitters’ to 46% for fruit from trees on ‘F6P12′. A reduced range of variability was recorded for vitamin C, the content of which ranged from 655 mg L−1 to 720 mg L−1 (‘Carrizo’ citrange and ‘F6P12′, respectively) and did not differ among fruits from trees on different rootstocks. For “blood oranges”, anthocyanin content is a quality trait of paramount importance and is characterized by a high degree of variation from year to year, even within the canopy. This variation is imposed by several environmental factors, among which temperature is prevalent (Chen et al., 2015). Compared with other fruit crops such as grape, peach and sweet cherry (Landi et al., 2014; Reig et al., 2016; Cheng et al., 2017), few studies have focused on the influence of rootstock on anthocyanin content in pigmented oranges (Incesu et al., 2013); rather they focused on the yield, sugar content and acid content in the fruit (Tribulato, 1979; Continella and La Rosa, 1985; Reforgiato Recupero et al., 2009). Our results clearly demonstrate that rootstock affect anthocyanin biosynthesis and accumulation in citrus. Whereas ‘Bitters’ combined with ‘Troyer’ and ‘Carrizo’ induced a significantly higher level of anthocyanins in fruit pulp, ‘Swingle’ citrumelo induced the lowest levels of pigmentation during the two years of this study. This result, coupled with the low yield observed during the first years, suggests that soil conditions are not optimal for this rootstock in this location. A noteworthy variation of fruit pigmentation was observed for both years, with fruit from trees on all rootstocks exhibiting a low anthocyanin content in 2016 compared with 2017 (Fig. 4). This finding indicates that climatic conditions during ripening are the key factors in determining anthocyanin biosynthesis and accumulation in blood oranges. The Mount Etna area in Sicily is favorable for the production of these oranges. This is mainly due to its climatic conditions and its day–night thermal range, which is considered the main trigger of fruit pigmentation. We observed that the daily temperature ranges during the ripening period (1 December − 15 March) were similar between the years observed (1185 in 2015-16 vs. 1084 in 2016-17) but that in the second year, corresponding to the higher
4. Conclusions The study highlighted the effect of several rootstocks in determining different vegetative, reproductive and qualitative aspects of ‘Tarocco Scirè’ and suggests that pedological conditions can be a limiting factor in the choice of alternative rootstocks to sour orange, at least in the considered study area. The results indicate that ‘C35′, ‘Bitters’, ‘Carpenter’ and ‘Furr’, rootstocks that have very recently been introduced to Italy, are the most suitable rootstocks for pigmented oranges under the conditions investigated in this study. These rootstocks positively affected yield precocity and enhanced fruit juice anthocyanin content. In this work, the effect of the rootstocks was demonstrated, and the influence of low temperatures on juice pigmentation was confirmed. Moreover, the determination of the total anthocyanin content revealed the greatest difference in the observed years, where the values were often more than doubled. In addition, several rootstocks were found to be unsuitable for production at this location. Almost all the trees in combination with ‘Severinia’ died and those in combination with ‘Swingle’ citrumelo produced late, likely because of sensitivity to the active lime levels of the soil. Soil conditions are important factors for use of rootstocks other than those of sour orange. These data need to be further corroborated by observations of the tested rootstocks in combination with other citrus varieties. Further studies, including newly released orange and mandarin cultivars, pigmented or not pigmented, are necessary to identify the most suitable scion/rootstock combinations in the post-CTV Italian citrus industry.
Acknowledgments The research was funded by the Sicilian Region, Italy (Project “Lotta al virus della Tristezza degli agrumi: sviluppo e innovazioni”) and by the University of Catania (Project “Sostenibilità del processo produttivo in filiere rappresentative dell’agricoltura mediterranea: innovazioni biologiche, tecniche ed agronomiche”).
Fig. 4. Anthocyanin content (mg L−1) recorded in 2016 and 2017 on fruit juice of ‘Tarocco Scirè’ sweet orange grafted on the studied rootstocks.
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AOAC, 1995. Official Methods of Analysis, 16th ed. Association of Official Analytical Chemists, Washington DC. Butelli, E., Licciardello, C., Zhang, Y., Liu, J., Mackay, S., Bailey, P., Reforgiato Recupero, G., Martin, C., 2012. Retrotransposons control fruit specific, cold-dependent accumulation of anthocyanins in blood oranges. Plant Cell 24, 1242–1255. Caruso, M., Ferlito, F., Licciardello, C., Allegra, M., Strano, M.C., Di Silvestro, S., Russo, M.P., Pietro Paolo, D., Caruso, P., Las Casas, G., Stagno, F., Torrisi, B., Roccuzzo, G., Reforgiato Recupero, G., Russo, G., 2016. Pomological diversity of the Italian blood orange germplasm. Sci. Hort. 213, 331–339. Chen, C., Lo Piero, A.R., Gmitter, F., 2015. Pigments in citrus. In: Chen, C. (Ed.), Pigments in Fruits and Vegetables: Genomics and Dietetics. Springer, New York, pp. 165–187. Cheng, J., Wei, L., Mei, J., Wu, J., 2017. Effect of rootstock on phenolic compounds and antioxidant properties in berries of grape (Vitis vinifera L.) cv. ‘Red Alexandria’. Sci. Hort. 217, 137–144. Continella, G., La Rosa, G., 1985. Performance of Moro orange on eight rootstocks. Il recente contributo della ricerca allo sviluppo dell’agrumicoltura italiana. pp. 163–168. Crifò, T., Petrone, G., Lo Cicero, L., Lo Piero, A.R., 2012. Short cold storage enhances the anthocyanin contents and level of transcripts related to their biosynthesis in blood oranges. J. Agric. Food Chem. 60, 476–481. DOGV, 2006. Diari Oficial de la Comunitat Valenciana 5346. pp. 30321–30328. De Pascual-Teresa, S., Sanchez-Ballesta, M.T., 2008. Anthocyanins: from plant to health. Phytochem. Rev. 7, 281–299. Dugo, P., Mondello, L., Morabito, D., Dugo, G., 2003. Characterization of anthocyanin fraction of Sicilian blood orange juice by Micro-HPLC-ESI/MS. J. Agric. Food Chem. 51, 1373–1376. FAOSTAT, 2014. http://faostat3. fao.org. Fallico, B., Ballistreri, G., Arena, E., Brighina, S., Rapisarda, P., 2017. Bioactive compounds in blood oranges (Citrus sinensis (L.) Osbeck): level and intake. Food Chem. 215, 67–75. Federici, C.T., Kupper, R.S., Roose, M.L., 2009. http://plantbiology.ucr.edu/faculty/new %20citrus%20rootstocks%202009. pdf. Forner-Giner, M.A., Rodriguez-Gamir, J., Martinez-Alcantara, B., Quiñones, A., Iglesias, D.J., Primo-Millo, E., Forner, J., 2014. Performance of Navel orange trees grafted onto two new dwarfingrootstocks (Forner-Alcaide 517 and Forner-Alcaide 418). Sci. Hort. 179, 376–387. Fu, L., Chai, L., Ding, D., Pan, Z., Peng, S., 2016. A novel citrus rootstock tolerant to iron deficiency in calcareous soil. J. Am. Soc. Hortic. Sci. 141, 112–118. Fuleki, T., Francis, F.J., 1968. Quantitative methods for anthocyanins: determination of individual anthocyanins in cranberry and cranberry products. J. Food Sci. 33, 471–478. García-Sánchez, F., Pérez-Pérez, J.G., Botía, P., Martínez, V., 2006. The response of young mandarin trees grown under saline conditions depends on the rootstock. Eur. J. Agron. 24, 129–139. Grosso, G., Galvano, F., Mistretta, A., Marventano, S., Nolfo, F., Calabrese, G., Buscemi, S., Drago, F., Veronesi, U., Scuderi, A., 2013. Red orange: experimental models and epidemiological evidence of its benefits on human health. Oxid. Med. Cell. Longevity 1–11. Incesu, M., Çimen, B., Yesiloglu, T., Yilmaz, B., 2013. Rootstock effects on yield, fruit quality, rind and juice color of Moro blood orange. J. Food, Agric. Environ. 11, 867–871.
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Influence of different rootstocks on yield precocity and fruit quality of ‘Tarocco Scirè’ pigmented sweet orange
T
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A. Continellaa, C. Pannitteria, S. La Malfaa, , P. Leguab, G. Distefanoa, E. Nicolosia, A. Gentilea a
Department of Agriculture, Food and Environment, University of Catania, Via Valdisavoia, 5, 95123 Catania, Italy Plant Sciences and Microbiology Department, Miguel Hernández University, Research Group in Plant Production and Technology, Ctra. de Beniel, km 3,2. 03312 Orihuela, Alicante, Spain b
A R T I C L E I N F O
A B S T R A C T
Keywords: Anthocyanins Blood orange Citrus Scion/rootstock combination Trifoliate orange hybrids
Several studies in citrus-producing countries are currently being carried out to select and evaluate rootstocks that are tolerant to Citrus Tristeza Virus (CTV) and can be adopted in different citrus production areas. An evaluation of rootstock suitability must consider the productive and qualitative features as well as the adaptability to varied environmental conditions (i.e., soil characteristics). Additionally, some varieties present qualitative aspects that are appreciated by consumers but can be affected by the use of different rootstocks. In Italy, the qualitative traits of pigmented or blood oranges, which are characterized by the presence of anthocyanins in the peel and flesh, are strongly influenced by several factors, including the scion/rootstock combination. The objective of this study was to evaluate and compare the influence of ten rootstocks on yield precocity and fruit quality of ‘Tarocco Scirè’ pigmented sweet orange in a Sicilian area within the Protected Geographical Indication (GPI) “Arancia Rossa di Sicilia” production district. Five of the ten rootstocks, namely, ‘Bitters’, ‘Carpenter’, ‘Furr’, ‘F6P12®’ and ‘F6P13′, have recently been released and produced good yields in limiting soil conditions. In this study, the important role of rootstock in determining the organoleptic quality, specifically the sugar content, and the anthocyanin concentrations in both the pulp and the juice was demonstrated. Some of the rootstocks that were recently introduced in Italy, i.e., ‘Bitters’ and ‘Furr’, were promising because they positively influenced several agronomic and qualitative parameters in the tested conditions, positively affected the yield precocity and enhanced the fruit juice anthocyanin content. Overall, these results contribute to the assessment of the role of different rootstocks in the post-CTV Italian citrus industry.
1. Introduction The use of rootstocks in fruit tree crops is important for plant performance and yield quality. For decades, sour orange (Citrus aurantium L.) has been widely used in the Mediterranean citrus industry because it was considered the most suitable rootstock in several citrus-growing areas for its good productivity in different environmental and pedological conditions, including calcareous soils. Its tolerance to many fungal diseases, such as Phytophthora spp., and to viroids, such as exocortis (CEVd) and xyloporosis (CCaVd), is an important element that brought sour orange into wider use. However, its intolerance to Citrus Tristeza Virus (CTV) impedes its use in new plantings of orange and mandarin orchards due to the diffusion of the virus (Moreno et al., 2008). To overcome this problem, citranges [Citrus sinensis (L.) Osb x Poncirus trifoliata (L.) Raf.] and other intergeneric hybrids (i.e., ‘Swingle’ citrumelo) tolerant to CTV have been used. However, the search for alternative rootstocks and their evaluation with different scion
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combinations and in various environmental conditions are still important goals to achieve in citrus-producing countries (Louzada et al., 2008; Reforgiato Recupero et al., 2009; Legua et al., 2014; Fu et al., 2016). Recently, research institutions from several countries have released new promising rootstocks; among these, the ‘Bitters’, ‘Carpenter’ and ‘Furr’ intergeneric hybrids [C. sunki Hort. ex Tan. x P. trifoliata (L.) Raf.] were released by the University of California, Riverside (UCR) (Federici et al., 2009) and are reported to be tolerant to calcareous soil and to produce good yields. Similarly, from the breeding program started in 1968 at CREA, Acireale, Italy, the rootstocks ‘F6P12®’ and ‘F6P13′ [C. latipes x P. trifoliata (L.) Raf.] have been selected for their good vegetative and productive performance (Reforgiato Recupero et al., 2009). Italy holds the 11th place in terms of world citrus production, with approximately 2.7 million tons (FAOSTAT, 2014), and half of the Italian cultivation area is in Sicily. In this region, sweet orange [Citrus sinensis (L.) Osbeck] cultivation represents 70% of the pigmented
Corresponding author. E-mail address: [email protected] (S. La Malfa).
https://doi.org/10.1016/j.scienta.2017.11.006 Received 1 August 2017; Received in revised form 27 October 2017; Accepted 1 November 2017 Available online 20 November 2017 0304-4238/ © 2017 Elsevier B.V. All rights reserved.
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cultivars (the so-called “blood oranges”). Catania Plain, at the foothills of Etna Volcano, is the most suitable production area for anthocyanin biosynthesis (La Rosa, 2012) and is within the Protected Geographical Indication (GPI) “Arancia Rossa di Sicilia” production district. Among the Italian blood oranges, ‘Tarocco’, with its several clones (including ‘Tarocco Scirè’, as used in the present study), is most famous for its greater peelability, taste and nutraceutical properties compared to blonde oranges, which are determined by the presence of anthocyanins and are responsible for their attractive red brilliant color (Lo Piero, 2015). ‘Moro’, which is deeper in color, is the second most widely cultivated pigmented variety in Italy. Specific environmental conditions, such as marked night/day thermal excursions, are considered to play an important role in pigment biosynthesis and its accumulation in fruits of selected genotypes (Rapisarda and Giuffrida, 1994; De PascualTeresa and Sanchez-Ballesta, 2008; Butelli et al., 2012), thus improving nutritional value and consumer acceptance. The anthocyanin contents in blood oranges, particularly in ‘Tarocco’ clones grafted onto sour orange, have been investigated extensively (Maccarone et al., 1998; Rapisarda and Russo, 2003; Fallico et al., 2017), primarily for their health value (Dugo et al., 2003; Proteggente et al., 2003; Grosso et al., 2013), but little has been reported on the effect of rootstocks on the qualitative parameters of blood oranges (Incesu et al., 2013). Since pigmented varieties are currently high-value products for the Italian citrus industry, it is important to select for these cultivars the most suitable rootstocks for different pedoclimatic conditions. In this work, we evaluated the influence of several CTV-resistant rootstocks on the yield precocity and fruit quality of a pigmented sweet orange line, namely, ‘Tarocco Scirè’, in an environment suitable for the cultivation of blood oranges.
2014. The number of harvested fruits, total production per tree and mean fruit weight were determined. The yield efficiency index for 2016/2017 was calculated as the ratio of yield to canopy volume and expressed as kg/m3. 2.3. Morphological and physicochemical parameters determination Starting in season 2015/2016 harvest, fifty representative pooled fruits from each rootstock combination were selected, individually weighed, measured and then used for juice extraction. Fruit height, equatorial diameter and rind thickness (mm) were measured using an electronic digital slide gauge (model CD-15 DC; Mitutoyo (UK) Ltd, Telford, UK) to within 0.01 mm accuracy. Peel color was recorded on two opposite points of the equatorial region for each fruit using a Minolta CR-400 chroma-meter (Minolta Corp., Osaka, Japan) according to the methodology described by Pannitteri et al. (2017). The results were expressed as a citrus color index (CCI = a*1000/L*b), where a* indicates chromaticity on a green (−) to red (+) axis and b* indicates chromaticity on a blue (−) to yellow (+) axis; this index is widely used in the citrus industry as a maturation index (DOGV, 2006). Fruit juice was extracted with a commercial juice extractor (Kenwood Citrus Juicer JE290, UK). Three juice samples, from the pooled juice of six fruits from 3 replicates per rootstock combinations, were used for chemical analyses. Juice was weighed and expressed as a percentage of the total fruit weight. The Total Solid Soluble (TSS) content was determined using a digital refractometer (Atago CO., LTD, model PR-32 α, Tokyo, Japan), with the results expressed as °Brix. Titratable acidity (TA) was determined by potentiometric titration (Hach, TitraLab AT1000 Series) of the juice with 0.1 N NaOH beyond pH 8.1 according to the AOAC method (AOAC, 1995), with the results expressed as g L−1 of citric acid equivalent. Ripening index (RI) was calculated as the ratio between TSS and TA. Vitamin C (L-ascorbic acid) was determined using an automatic titration apparatus (702 SM Titrino, Metrohm, Herisau, Switzerland) with 0.001 M I2, and the results were expressed as mg L−1. Total anthocyanin content (TAC) was determined spectrophotometrically by the pH differential method (Fuleki and Francis, 1968), where the absorbance was measured using a spectrophotometer (NanoDrop 2000, Thermo Scientific) at 510 and 700 nm in buffers at pH 1.0 and 4.5. The results were expressed as the mg of cyanidin-3glucoside equivalents per liter of fresh weight.
2. Materials and methods 2.1. Plant material Ten rootstocks, ‘Troyer’, ‘Carrizo’ citrange, ‘C35′ [C. sinensis (L.) Osb. cv. ‘Ruby’ x P. trifoliata (L.) Raf.], ‘Swingle’ citrumelo [C. paradisi (Macfadyen) x P. trifoliata (L.) Raf.], ‘Bitters’, ‘Carpenter’, ‘Furr’, ® ‘F6P12 ’, ‘F6P13′ and ‘Severinia’ [Severinia buxifolia (Poir.) Ten.], were evaluated in combination with ‘Tarocco Scirè’, a virus free selection obtained by micro-grafting a scion. Some of the selected rootstocks have been recently released, and others are already widely used in citrus producing areas. Rootstocks were propagated from seeds and plants were T-budded in the nursery with ‘Tarocco Scirè’, a medium-ripening line of blood oranges. This line was chosen to better evaluate the effect of rootstock on fruit pigmentation because this line is characterized by a rather low content of anthocyanins in the fruit (Caruso et al., 2016). After one year, budded plants were transplanted. The experimental field was established in 2010 in Catania Plain (37°17′04′’N, 14°53′16′’E). The experimental design was a complete randomized block, with five plots of 20 trees and each tree spaced 5 m x 3 m apart. The texture components of the soil were 68.6% sand, 23.6% loam, and 7.8% clay. In the experimental field, the pH values were 8.5, and the content of active lime was 3.0%. The orchard was subjected to standard cultural practices.
2.4. Statistical analysis Statistical analyses were performed using STATISTICA 6.0 (Statsoft Inc., Tulsa, OK) and used to test the significance of each variable (P ≤ 0.05). A basic descriptive statistical analysis was followed by an analysis of variance test for mean comparisons. The method used to discriminate among the means (Multiple Range Test) was Fisher’s Least Significant Difference (LSD) procedure at a 95.0% confidence level. 3. Results and discussion 3.1. Vegetative and yield determinations The different rootstocks significantly affected several growth parameters of ‘Tarocco Scirè’ (Fig. 1). The canopy volume, as measured in November 2016, was larger in plants budded on ‘Furr,’ ‘Carpenter’ and ‘C35′ (10.1, 9.5 and 9.4 m3, respectively). The smallest canopy volume was observed in combination with ‘Troyer’ citrange (4.7 m3). The TCSA values ranged from 139 cm2 (for ‘Swingle’ citrumelo) to 75 cm2 (for ‘Bitters’ and ‘Troyer’citrange) and were not always correlated with the canopy volume; for instance, ‘Carpenter’ and ‘C35′ exhibited a high canopy volume but reduced TCSA. Among the rootstock released by UCR, ‘Bitters’ was less vigorous (i.e., it was smaller and had shorter branches) than were ‘Carpenter’ and ‘Furr,’ as observed by other
2.2. Vegetative and yield determinations The trunk circumference (10 cm above the bud union) and canopy volume were measured annually for 6 years from 2010 through 2016. Trunk cross sectional area (TCSA) was calculated by the equation: TCSA = π ( diameter )2. The tree volume was calculated by the equation: 2 V = 0.524 x height x width2 because the tree shape was assumed to be one-half of a prolate spheroid (Morse and Robertson, 1987). Yield was recorded beginning with the first harvest, which occurred in 2013/ 63
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Fig. 1. Canopy volume and trunk cross sectional area (TCSA) recorded for ‘Tarocco Scirè’ on different rootstocks in 2016.
respectively) but were less productive during the first three years, resulting in lower cumulative yields. ‘F6P13′ and ‘Severinia’ showed the lowest yield: the former produced significantly only in 2016/2017, with an average yield of 13.4 kg/tree. In contrast, trees in combination with ‘Severinia’ only produced in the first year of production because all the plants grafted with this rootstock died in the second year. Our hypothesis is that this negative performance was due to the very high sensitivity of this rootstock to active lime. In the sixth year of observation, the highest values of yield efficiency (Fig. 3) were registered for ‘Bitters’ (8.1 kg/m3), followed by ‘Carpenter’, ‘C35′ and ‘Furr’ (7.5, 7.1 and 7.1 kg/m3, respectively). ‘Swingle’ citrumelo and ‘F6P13′ were the rootstocks with the lowest yield efficiency (3.0 and 2.8 kg/m3, respectively).
authors (Siebert et al., 2010). This result appears to be interesting in the context of citrus rootstocks, as only a few are considered capable of limiting vegetative growth and giving good yields. The only rootstock that resulted in dwarfing in the citrus was the ‘Flying Dragon’ trifoliate orange (Roose, 1986). More recently, two hybrids, namely, FA-517 [Citrus nobilis Lour × Poncirus trifoliata L. (Raf.)] and FA-418 [Troyer citrange × C. deliciosa (Ten)] presented dwarfing properties in scions (Forner-Giner et al., 2014). Among citrus rootstocks, ‘Swingle’ citrumelo has generally been considered vigorous (Wutscher, 1974). In our study conditions, the canopy volume of this rootstock was lower than those of ‘Furr’, ‘Carpenter’ and ‘C35′. For citranges, ‘Troyer’ showed the lowest values of both the vegetative parameters, whereas ‘Carrizo’ presented intermediate values. ‘Severinia’ data are not reported because all the plants grafted from this rootstock died by the second year. Fruit production started in the third year for all rootstocks except ‘F6P13′, which started to produce fruit in the fourth year. In the fourth year of production, the highest cumulative yields were obtained for ‘C35′ and ‘Bitters’ (Fig. 2). ‘Furr’ and ‘Carpenter’ produced more than ‘Bitters’ and ‘C35′ did in the fourth year (70 and 71 kg vs. 57 and 66 kg,
3.2. Morphological and physicochemical parameters determination The highest fruit weights were recorded for trees grafted from ‘Carrizo’ (218 g), ‘C35′ (218 g) and ‘Bitters’ (212 g), which was significantly different from trees grafted from ‘Swingle’ citrumelo, which Fig. 2. Cumulative yield recorded on ‘Tarocco Scirè’ on different rootstocks.
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Fig. 3. Yield efficiency of ‘Tarocco Scirè’ on different rootstocks in 2016/2017.
Table 1 Fruit physical parameters (average of two years 2015/2016 and 2016/2017) of ‘Tarocco Scirè’ sweet oranges grafted on the studied rootstocks.a,b
‘Carrizo’ ‘Troyer’ ‘C35′ ‘Citrumelo’ ‘Bitters’ ‘Carpenter’ ‘Furr’ ‘F6P12′
Fruit weight (g)
Fruit height (mm)
Fruit diameter (mm)
Rind thickness (mm)
Citrus color index
218 201 218 170 212 195 200 204
69.9 65.8 69.1 61.5 66.5 82.7 79.9 74.4
68.6 65.1 67.9 61.8 65.6 80.0 77.4 73.0
4.5 4.4 4.6 4.0 4.2 4.5 4.4 4.2
6.6 ± 1.5abc 6.8 ± 1.5abc 6.5 ± 1.5bc 5.5 ± 2.9d 7.1 ± 2.2ab 7.2 ± 1.5a 7.2 ± 1.6a 6.2d ± 1.5c
± ± ± ± ± ± ± ±
6a* 4a 3a 4b 4a 4ab 3a 4a
± ± ± ± ± ± ± ±
22.1bc 18.6bc 20.9bc 18.1c 18.5bc 11.5a 6.4a 14.5ab
± ± ± ± ± ± ± ±
19.7bc 17.9bc 18.9bc 18.3c 18.2bc 10.0a 5.3a 13.9ab
± ± ± ± ± ± ± ±
1.2a 1.5a 1.4a 1.3a 1.2a 1.1a 1.5a 1.5a
*Values along columns with different letters are different for p ≤ 0.05. a No data are reported for F6P13 since no production was recorded in 2015/16. b No data are reported for ‘Severinia’ because all the plants died in the second year.
Fruits from trees on ‘Carrizo’ citrange and ‘Bitters’ showed the highest TSS values (11.1°Brix), but these values were not significantly different from those of ‘Troyer’ citrange and ‘Furr’, and ‘Swingle’ citrumelo, ‘Carpenter’ and ‘F6P12′ showed the lowest values (9.7, 9.8 and 9.9°Brix, respectively). Rootstocks also significantly influenced TA accumulation in the fruits. The highest TA content was found in fruits from trees on ‘Furr’ (9.7 g citric acid L−1), and the lowest was found in fruits from trees on ‘Carpenter’ (7.8 g citric acid L−1). Conversely, other studies found that the effects of rootstock on fruit juice acidity were non-significant. These results were found in fruits of ‘Lane Late’ trees in combination with C. macrophylla, C. volkameriana and Cleopatra mandarin (Legua et al., 2011b) and in ‘Clemenules’ mandarin grafted on Cleopatra mandarin
had the lowest fruit weight (170 g) (Table 1). Fruit from ‘Swingle’ trees also had the lowest height and fruit diameter. The largest fruit diameters were measured for ‘Carpenter’, ‘Furr’ and ‘F6P12′ (80.0, 77.4 and 73.0 mm, respectively). No significant differences were recorded for rind thickness, which ranged from 4.0 mm for ‘Swingle’ citrumelo fruit to 4.6 mm for fruit grafted from C35 trees. The Citrus Color Index showed the highest values on fruits of plants grafted onto ‘Carpenter’, ‘Furr’ and ‘Bitters’, whereas a paler red color was observed on ‘Tarocco Scirè’ fruits in combination with ‘Swingle’ citrumelo (Table 1). TSS and TA are the most relevant parameters for orange juice quality determination. In this work, we observed significant differences in these two parameters among trees on different rootstocks (Table 2).
Table 2 Fruit qualitative parameters (average of two years 2015/2016 and 2016/2017) of ‘Tarocco Scirè’ sweet oranges grafted on the studied rootstocks.a,b
‘Carrizo’ ‘Troyer’ ‘C35′ ‘Citrumelo’ ‘Bitters’ ‘Carpenter’ ‘Furr’ ‘F6P12′
TSS (°Brix)
TA (g L−1)
RI (TSS/TA)
Juice (%)
Vitamin C (mg L−1)
11.1 ± 0.5a* 10.9 ± 0.2ab 10.2 ± 0.8bc 9.7 ± 0.4c 11.1 ± 0.8a 9.8 ± 0.9c 10.4 ± 0.3abc 9.9 ± 1.2c
8.5 8.8 8.7 9.3 8.0 7.8 9.7 8.9
11.6 12.4 11.8 10.5 13.9 12.6 10.8 11.1
51.6 49.5 47.9 50.7 51.9 48.8 47.7 45.8
655 664 666 677 713 659 668 720
± ± ± ± ± ± ± ±
0.7bcd 0.6abc 0.6bcd 0.7ab 0.6 cd 0.7d 1.0a 1.1ab
*Values along columns with different letters are different for p ≤ 0.05. a No data are reported for F6P13 since no production was recorded in 2015/16. b No data are reported for ‘Severinia’ because all the plants died in the second year.
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± ± ± ± ± ± ± ±
1.5ab 0.9bc 1.0 cd 1.1d 1.3a 1.1bc 1.0d 0.7d
± ± ± ± ± ± ± ±
5.8a 6.3ab 4.0ab 2.6ab 3.5a 5.0ab 3.2ab 0.8b
± ± ± ± ± ± ± ±
73a 22a 103a 64a 69a 58a 61a 69a
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pigmentation levels, there were more hours with temperatures below 6 °C (293 vs. 454, respectively). This result is consistent with the findings of several authors, who noted the role of cold temperatures in enhancing anthocyanin biosynthesis in blood oranges during post-harvest treatments (Crifò et al., 2012; Pannitteri et al., 2017).
and Carrizo citrange (García-Sánchez et al., 2006). The TSS/TA ratio is an important qualitative parameter of Citrus fruits and is the most widely used method for estimating the citrus maturity level (Legua et al., 2011a). The fruits of trees on ‘Bitters’ showed the highest ripening index (13.9), whereas ‘Swingle’ citrumelo had the lowest index (10.5), although these values were not significantly different from those of ‘F6P12′ and ‘Furr.’ Significant differences were found for juice content in the fruit: its percentage ranged from 52% for fruit from trees on ‘Bitters’ to 46% for fruit from trees on ‘F6P12′. A reduced range of variability was recorded for vitamin C, the content of which ranged from 655 mg L−1 to 720 mg L−1 (‘Carrizo’ citrange and ‘F6P12′, respectively) and did not differ among fruits from trees on different rootstocks. For “blood oranges”, anthocyanin content is a quality trait of paramount importance and is characterized by a high degree of variation from year to year, even within the canopy. This variation is imposed by several environmental factors, among which temperature is prevalent (Chen et al., 2015). Compared with other fruit crops such as grape, peach and sweet cherry (Landi et al., 2014; Reig et al., 2016; Cheng et al., 2017), few studies have focused on the influence of rootstock on anthocyanin content in pigmented oranges (Incesu et al., 2013); rather they focused on the yield, sugar content and acid content in the fruit (Tribulato, 1979; Continella and La Rosa, 1985; Reforgiato Recupero et al., 2009). Our results clearly demonstrate that rootstock affect anthocyanin biosynthesis and accumulation in citrus. Whereas ‘Bitters’ combined with ‘Troyer’ and ‘Carrizo’ induced a significantly higher level of anthocyanins in fruit pulp, ‘Swingle’ citrumelo induced the lowest levels of pigmentation during the two years of this study. This result, coupled with the low yield observed during the first years, suggests that soil conditions are not optimal for this rootstock in this location. A noteworthy variation of fruit pigmentation was observed for both years, with fruit from trees on all rootstocks exhibiting a low anthocyanin content in 2016 compared with 2017 (Fig. 4). This finding indicates that climatic conditions during ripening are the key factors in determining anthocyanin biosynthesis and accumulation in blood oranges. The Mount Etna area in Sicily is favorable for the production of these oranges. This is mainly due to its climatic conditions and its day–night thermal range, which is considered the main trigger of fruit pigmentation. We observed that the daily temperature ranges during the ripening period (1 December − 15 March) were similar between the years observed (1185 in 2015-16 vs. 1084 in 2016-17) but that in the second year, corresponding to the higher
4. Conclusions The study highlighted the effect of several rootstocks in determining different vegetative, reproductive and qualitative aspects of ‘Tarocco Scirè’ and suggests that pedological conditions can be a limiting factor in the choice of alternative rootstocks to sour orange, at least in the considered study area. The results indicate that ‘C35′, ‘Bitters’, ‘Carpenter’ and ‘Furr’, rootstocks that have very recently been introduced to Italy, are the most suitable rootstocks for pigmented oranges under the conditions investigated in this study. These rootstocks positively affected yield precocity and enhanced fruit juice anthocyanin content. In this work, the effect of the rootstocks was demonstrated, and the influence of low temperatures on juice pigmentation was confirmed. Moreover, the determination of the total anthocyanin content revealed the greatest difference in the observed years, where the values were often more than doubled. In addition, several rootstocks were found to be unsuitable for production at this location. Almost all the trees in combination with ‘Severinia’ died and those in combination with ‘Swingle’ citrumelo produced late, likely because of sensitivity to the active lime levels of the soil. Soil conditions are important factors for use of rootstocks other than those of sour orange. These data need to be further corroborated by observations of the tested rootstocks in combination with other citrus varieties. Further studies, including newly released orange and mandarin cultivars, pigmented or not pigmented, are necessary to identify the most suitable scion/rootstock combinations in the post-CTV Italian citrus industry.
Acknowledgments The research was funded by the Sicilian Region, Italy (Project “Lotta al virus della Tristezza degli agrumi: sviluppo e innovazioni”) and by the University of Catania (Project “Sostenibilità del processo produttivo in filiere rappresentative dell’agricoltura mediterranea: innovazioni biologiche, tecniche ed agronomiche”).
Fig. 4. Anthocyanin content (mg L−1) recorded in 2016 and 2017 on fruit juice of ‘Tarocco Scirè’ sweet orange grafted on the studied rootstocks.
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