Trifoliate hybrids as alternative rootstocks for ‘Valencia’ sweet orange under rainfed conditions

Scientia Horticulturae 235 (2018) 397–406

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Trifoliate hybrids as alternative rootstocks for ‘Valencia’ sweet orange under rainfed conditions

T

André Luiz Fadela,1, Eduardo Sanches Stuchib, Hilton Thadeu Zarate Coutoa, ⁎ Yuri Caires Ramosa,2, Francisco de Assis Alves Mourão Filhoa, a b

Universidade de São Paulo, Escola Superior de Agricultura “Luiz de Queiroz”, 13418-900, Piracicaba, SP, Brazil Embrapa Mandioca e Fruticultura, Rua Embrapa, Cruz das Almas, BA, Brazil

A R T I C L E I N F O

A B S T R A C T

Keywords: Citrus sinensis Drought tolerance Fruit quality Poncirus trifoliata Yield

Considering the low diversity of rootstocks in the Brazilian citrus industry, as well as in other important citrus production regions, here we investigated the yield, fruit quality, plant size and drought tolerance of ‘Valencia’ sweet orange [Citrus sinensis (L.) Osbeck] grafted onto eleven rootstocks in the northern region of São Paulo State, Brazil. The trial was installed with no supplementary irrigation. Various combinations (scion/rootstock) were planted in March 2007 and submitted to measurements of yield and fruit quality, canopy volume, yield efficiency, growth rate, and drought tolerance. We detected high yield in ‘Valencia’ sweet orange grafted onto “CNPMF 003” ‘Rangpur’ lime rootstock. Regarding other measurements, it was also attributed to two combinations high fruit quality of ‘Valencia’ sweet orange and to other three combinations satisfactory drought tolerance compared to two ‘Rangpur’ lime clones. ‘Valencia’ sweet orange trees grafted onto two rootstocks were suitable for high-density planting. As an alternative to ‘Rangpur’ lime, the ‘Sunki’ mandarin × P. trifoliata ‘English’ and ‘C-13’ “S” citrange rootstocks showed potential as rootstocks for ‘Valencia’ sweet orange in rainfed conditions.

1. Introduction Citrus (sweet oranges, mandarins, limes, grapefruits) are the most important fruit group produced in the world, accounting for more than 135 million tons per year; Brazil represents 13.6% of this production (FAO, 2017). However, pest and disease problems affect the entire citrus industry chain in Brazil. Since the 1950s, ‘Rangpur’ lime (Citrus limonia Osbeck) has been used as the main rootstock in São Paulo State, Brazil, principally because of its tolerance to the citrus tristeza virus and drought (Pompeu Junior, 1991), as well as high vigor in the nursery, satisfactory yield, and fruit quality (Pompeu Junior, 2005). Given the ‘Rangpur’ lime’s susceptibility to citrus sudden death (CSD) (Bové and Ayres, 2007), it has been suggested that an increase in the diversification of rootstock use in Brazil is needed. However, most of the disease tolerance species perform poorly under drought conditions. In Brazil, besides drought, some growing regions experience high temperatures, which might limit the use of rootstocks that require supplementary irrigation.

Rootstock and rootstock-scion combinations play an important role in the citrus industry, affecting plant yield, fruit quality (Castle, 1995; Fellers, 1985), and tolerance to biotic and abiotic factors (Castle, 1987). Despite the relatively large amount of research addressing citrus rootstocks, citrus orchards typically have low rootstock diversification. The world population is projected to exceed 9 billion people by 2050, thus requiring an increase in global food production of up to 70%, which will lead to an increase in fresh water demand, likely contribute to food price increases. Agriculture is responsible for approximately 70% of all fresh water consumption, and can account for up to 90% fresh water consumption in less developed Countries (UNESCO, 2015). Efficient water use through improved irrigation and more efficient cultivars would greatly reduce the demand for fresh water. Considering the low diversity of rootstocks used in Brazil and the need for more efficient species for sweet orange production in regions subject to drought, here we aimed to determine the response of ‘Valencia’ sweet orange [C. sinensis (L.) Osbeck] grafted onto eleven rootstocks in rainfed conditions. This work was done in the northern

⁎

Corresponding author. E-mail addresses: [email protected] (A.L. Fadel), [email protected] (E.S. Stuchi), [email protected] (H.T.Z. Couto), [email protected] (Y.C. Ramos), [email protected] (F.d.A.A. Mourão Filho). 1 Present address: Centro de Citricultura “Sylvio Moreira”, 13490-970, Cordeirópolis, SP, Brazil. 2 Present address: Universidade Federal do Recôncavo da Bahia, 44380-000, Cruz das Almas, BA, Brazil. https://doi.org/10.1016/j.scienta.2018.01.051 Received 18 September 2017; Received in revised form 16 January 2018; Accepted 17 January 2018 Available online 20 March 2018 0304-4238/ © 2018 Elsevier B.V. All rights reserved.

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between yield (kg fruits plant−1) and canopy volume (m3), expressed in kg of fruit per m3 of the canopy. In addition to plant size and yield measurements, the growth rate (GR) was calculated by an increase of canopy volume (V), expressed in canopy volume increment year−1.

region of São Paulo State, Brazil, measuring yield, fruit quality, tree size, and drought tolerance. 2. Material and methods 2.1. Experimental site and statistical design

2.4. Plant yield The experimental grove was planted in a commercial citrus farm in the northern region of São Paulo State, Brazil (latitude 20°19′39′′S; longitude 48°41′16′′W) in a Red-Dark Latosol soil (A moderate, medium to clay texture). The regional climate is Aw (tropical, rainy with dry winter) according to the Köppen classification (annual mean minimum temperature, 17.0 °C; annual mean maximum temperature, 30.7 °C) with 1430 mm annual rainfall (CEPAGRI, 2014). The various combinations (scion/rootstock) were planted in March 2007 in 6.0 × 2.5 m plots without supplementary irrigation. The experimental design was randomized blocks, with 11 treatments (rootstocks), three replications, and five trees per plot.

The yield was measured from 2009, two years after planting, and repeated annually until 2014, totaling six annual harvests. The fruit harvest was carried out between October and November of each year, according to the ripening season of ‘Valencia’ sweet orange in the growing conditions of the experiment. The fruits of each plot were grouped in a specific bag for fruit harvest (800 kg capacity). After being hoisted, the total mass was determined with a digital dynamometer. Fruit production values were expressed in kg of fruit plant−1 and analyzed as mean production and accumulated production in six annual harvests, from 2009 to 2014.

2.2. Rootstocks origin

2.5. Fruit quality

The rootstock origins are as follows: “CNPMF 003” ‘Rangpur’ lime (C. limonia Osbeck), nuclear clone selection, obtained from a common ‘Rangpur’ lime clone (Soares Filho, W., personal communication); “Santa Cruz” ‘Rangpur’ lime (C. limonia Osbeck), cultivar selected by “Santa Bárbara” ‘Rangpur’ lime mutation (Soares Filho et al., 1999); ‘Malvásio SRA 115’ (C. reticulata Blanco), ‘East Índia SRA 414’ (C. reticulata Blanco), ‘C-54-4-4 SRA 337’ (C. reticulata Blanco) and ‘À Peau Lisse SRA 267’ (C. deliciosa Ten.) mandarins, cultivars introduced to Brazil with other mandarins cultivars and hybrids from Italian, Corsican, Portuguese, and Spanish germplasm banks for studies related to citrus variegated chlorosis (CVC) (Silva et al., 2004); ‘Sunki’ × Poncirus trifoliata ‘Benecke’ (C. sunki (Hayata) hort. ex Tanaka × Poncirus trifoliata (L.) Raf.) mandarin, hybrid developed via controlled crossing by United States Department of Agriculture (USDA), Indio Research Station, California (Bowman and Rouse, 2006); ‘C-13’ “S” citrange [C. sinensis (L.) Osbeck × P. trifoliata (L.) Raf.], hybrid introduced to Brazil in 1997, from the Instituto Valenciano de Investigaciones Agrarias (IVIA), Valencia (Spain), which showed good performance when used as rootstock for ‘Malay Lemon’ acid lime (Stuchi et al., 2006); ‘Cleopatra’ mandarin × Poncirus trifoliata ‘Rubidoux’ (C. reshni hot. ex Tanaka × P. trifoliata (L.) Raf.) mandarin, hybrid present in germplasm bank of Embrapa Mandioca and Fruticultura, originating from USDA (Soares Filho, W., personal communication); ‘Sunki’ × Poncirus trifoliata ‘English’ (C. sunki (Hayata) hort. ex Tanaka × P. trifoliata (L.) Raf) mandarin, hybrid originated from Palmira, Colombia (Soares Filho, W., personal communication); “Rohde Red” ‘Valencia’ sweet orange + ‘Volkamer’ lemon [C. sinensis (L). Osbeck plus C. volkameriana], somatic hybrid developed for studies related to diseases tolerance (Costa et al., 2003).

Measurements related to fruit quality was performed from 2010 to 2013. For this, 15 fruits per plot were collected, totaling 45 fruits per treatment. Analyses were carried out in Bebedouro Experimental Station, São Paulo State, Brazil. Mass of fruits (FM), equatorial, and polar diameters were measured, followed by juice extraction in a mechanized extractor. The total juice mass (JM) of each plot was determined and the juice yield (JY), expressed in percentage of juice (%), was obtained by the equation: JY = (JM × 100)/FM The total soluble solids (TSS) was determined in a digital refractometer. A sample of 5 ml of juice per plot was collected after extraction. The values were obtained by direct reading on the refractometer, expressed in °Brix. Total acidity was determined by the titration method (0.1 N sodium hydroxide) according to Stenzel et al. (2003). The Technological Index (TI), expressed in kg of TSS box−1 (40.8 kg) was determined by the equation: TI = [(JY × TSS × 40.8) × 10000]

2.6. Plant tolerance to drought 2.6.1. Visual assessment To identify drought tolerant combinations, a visual assessment was carried out in 2010, 2011, and 2012, during the soil water deficiency period (August and September). These assessments consisted of three visual scores, based on trees under water stress, considering the criteria: (1) expressive leaf wilting, showing dried aspect or not; (2) slight leaf wilting, showing normal aspect; and (3) normal leaf, leaf wilting absence, as utilized by Stuchi et al. (2000).

2.3. Plant size and yield efficiency 2.6.2. Leaf water potential In addition to visual assessment, leaf water potential evaluations were carried out in 2012 and 2013. Four assessments were carried out per year, in March, August, October, and December. One leaf per plot was sampled and the water potential was determined with a pressure chamber, according to Kaufmann (1968). The leaves were collected at 06:00 am, and stored individually in sealed bags, which were packed in a thermal box.

Plant size, represented by the variable canopy volume (V), expressed in (m3), was evaluated in 2010, 2011, 2012, 2013, and 2014, after evaluation of fruit production. In 2010, 2011, and 2012 we measured the plant height (H), and plant diameter (D) (parallel and perpendicular to the tree row). In 2013 and 2014, the plant height (H) and only the diameter perpendicular to the tree row were measured, due to the excessive canopy overlap between trees. Then, the canopy volume was calculated from the mean values of each year using the equation:

2.7. Data analysis

V = 2/3 × π × (D/2) × H 2

The mean values of all variables related to the different scion/ rootstock combinations were submitted to homogeneity analysis of

The yield efficiency (YE) was determined through the relationship 398

399

Mean yield kg plant

−1

Means followed by different letters (lowercase) in columns are significantly different by Tukey test (P < 0.05). Means followed by different letters (uppercase) in lines are significantly different by Tukey test (P < 0.05). * significantly different by F test but not significant by Tukey test (P < 0.05). NS Not significant at 5% probability level.

4.74 E

10.34 D

44.69 AB

58.98 A

42.17 B

25.55 C

< 0.0001 0.1606NS 0.0566NS < 0.0001 (P) Value

< 0.0001

0.0001

0.0249

0.0004

0.1245NS

12.47 9.73 4.38 C.V. (%)

13.70

16.69

26.65

12.62

10.33

0.0164

11.44 17.19

13.39

a ab bc bc bc bc bc c c c c 44.70 35.61 33.54 33.54 30.03 29.07 28.10 27.90 27.64 26.31 25.58 35.35 29.63 27.68 31.78 30.60 25.85 28.52 17.27 20.37 16.95 17.05 68.93 42.71 40.38 45.81 33.70 38.66 41.22 49.14 33.97 44.71 24.59 75.27 75.52 62.53 65.15 60.54 57.85 54.11 40.08 51.06 51.52 55.14 64.72 43.10 49.42 39.75 43.05 43.64 36.98 47.87 38.22 43.82 40.97 15.81 a 16.57 a 13.64 ab 11.75 abc 9.15 abc 6.18 bc 5.62 c 10.95 abc 10.37 abc 7.13 bc 6.57 bc a a a a a a a a a a a 8.12 9.05 7.58 6.99 3.16 2.19 2.10 2.07 3.86 1.73 5.32 a ab bc bc ab ab ab bc c abc bc 5.79 5.14 3.15 3.35 4.69 5.00 5.06 3.41 2.43 4.08 3.53 ab ab ab a ab c c bc ab c bc 4.59 4.73 5.02 5.44 4.47 2.95 2.99 3.90 4.64 2.87 4.13

2009*

2010

2011

2012

2013

a ab ab ab b ab ab ab b ab b

2014

Average 2009 to 2014

268.20 213.65 201.23 201.22 180.20 174.37 168.55 167.39 157.83 165.86 155.39

a ab b b b b b b b b b

Accumulated yield kg tree−1 Yield kg plant−1

15.48 a 12.60 bc 9.74 cde 9.20 de 10.70 cde 14.57 ab 13.77 ab 10.42 cd 7.95 e 13.18 ab 9.88 de

Rootstocks ‘Sunki’ mandarin × P. trifoliata ‘English’ and “Santa Cruz” ‘Rangpur’ lime conferred to ‘Valencia’ sweet orange the best average yield (kg plant−1) and accumulated yield (kg plant−1) in the evaluated period (2009–2014) (Table 1). ‘Valencia’ sweet orange grafted onto ‘Sunki’ mandarin × P. trifoliata ‘English’ was also as early bearing as plants onto “Santa Cruz” and “CNPMF 003” ‘Rangpur’ lime in the 2010 harvest. On the other hand, ‘Valencia’ sweet orange grafted onto “CNPMF 003” ‘Rangpur’ lime was less productive than plants grafted onto ‘Sunki’ mandarin × P. trifoliata ‘English’ hybrid (Table 1). For the combinations involving ‘Valencia’ sweet orange onto “CNPMF 003” ‘Rangpur’ lime, ‘C-13’ “S” citrange, ‘Sunki’ mandarin × P. trifoliata ‘Benecke’, ‘À Peau Lisse SRA 267’ and ‘East India SRA 414’, mandarins were grouped in an statistically equally intermediate class, regarding yield (kg plant−1) over the six annual harvests (Table 1). Considering all scion/rootstock combinations together, the average harvest in each year (2009 through 2014) was higher in 2011, 2012, and 2013 than harvest in 2014 (Table 1). The correlation coefficient involving temperature and yield showed a negative correlation (Spearman’s correlation: −0.62231, P < 0.0001, maximum temperature × yield per year; −0.63643, P < 0.0001, minimum temperature × yield per year), suggesting that high temperatures negatively influenced the yield.

‘Sunki’ mandarin × P. trifoliata ‘English’ “Santa Cruz” ‘Rangpur’ lime “CNPMF 003” ‘Rangpur’ lime ‘C-13’ “S” citrange ‘Sunki’ mandarin × P. trifoliata ‘Benecke’ ‘À Peau Lisse SRA 267’ mandarin ‘East India SRA 414’ mandarin ‘Malvasio SRA 115’ mandarin ‘Cleópatra’ mandarin × P. trifolata ‘Rubidoux’ ‘C-54-4-4 SRA 337’ mandarin “Rohde Red” ‘Valencia’ orange + ‘Volkamer’ lemon

3.2. Plant average yield and plant cumulative yield

Growth rate m3 year−1

‘Sunki’ mandarin × P. trifoliata ‘English’, ‘C-54-4-4 SRA 337’, ‘East India SRA 414’, and ‘Peau Lisse SRA 267’ mandarins conferred to ‘Valencia’ sweet orange scion the best performance related to the plant size, characterized by the highest mean values of canopy volume between 2010 and 2014 (Table 1). The growth rates did not differ significantly when comparing ‘Valencia’ sweet orange grafted onto ‘Sunki’ mandarin × P. trifoliata (‘English’ and ‘Benecke’ selections), “Santa Cruz” ‘Rangpur’ lime and ‘C54-4-4 SRA 337’, ‘East India SRA 414’ and ‘À Peau Lisse SRA 267’ mandarins. ‘Valencia’ sweet orange grafted onto hybrids that had P. trifoliata as the genitor were equally efficient in fruit yield per m3, and did not differ from two ‘Rangpur’ lime selections (Table 1). Combinations grafted onto ‘Cleopatra’ mandarin × P. trifoliata ‘Rubidoux’, “CNPMF 003” ‘Rangpur’ lime, ‘C-13’ “S” citrange, ‘Sunki’ mandarin × P. trifoliata ‘Benecke’, and “Rohde Red” ‘Valencia’ sweet orange + ‘Volkamer’ lemon were the least vigorous, presenting lower plant size. ‘C-13’ “S” citrange and ‘Cleopatra’ mandarin × P. trifoliata ‘Rubidoux’ rootstocks showed good suitability for high-density planting, in addition to reduced canopy volume, and were the most yield efficient (kg m3 of the canopy) (Table 1).

YE kg m−3

3.1. Plant size, yield efficiency, and annual growth rate

Canopy volume m3

3. Results

Rootstock

Table 1 Mean values of canopy volume (m3), yield efficiency (YE) of fruits (kg m3), growth rate (m3year) from 2010 to 2014, annual yield from 2009 to 2014, average yield from 2009 to 2014, and accumulated yield from 2009 to 2014 of ‘Valencia’ sweet orange grafted onto eleven rootstocks. Colombia, Brazil.

variance (Box-Cox test). The variables that presented variance homogeneity were analyzed by F test, and the means were compared by the Tukey test (P < 0.05). After Box-Cox test analysis, leaf water potential did not show variance homogeneity, even after transformation. Therefore, this variable was analyzed by Friedman’s non-parametric test, and the means were compared by the Tukey’s test (P < 0.05). Variables related to fruit quality, yield, plant size, and yield efficiency were submitted to Spearman’s correlation analysis (Campos, 1983). The yield variable (kg plant−1) was also analyzed by Spearman’s correlation with rainfall data and with maximum and minimum mean temperatures. To analyze the relationship between the variables used to determine drought tolerance, leaf water potential and visual drought assessment data were submitted to simple linear regression analysis (Weisberg, 2005).

< 0.0001

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Table 2 Mass (g), equatorial diameter (mm), polar diameter (mm), total soluble solids (TSS), acidity, ratio, juice yield (JY) and technological index (TI) in fruits of ‘Valencia’ sweet orange grafted onto eleven rootstocks, from 2010 to 2013, Colombia, Brazil. Roostock

Mass g

‘Sunki’ mandarin × P. trifoliata ‘English’ “Santa Cruz” ‘Rangpur’ lime “CNPMF 003” ‘Rangpur’ lime ‘C-13’ “S” citrange ‘Sunki’ mandarin × P. trifoliata ‘Benecke’ ‘À Peau Lisse SRA 267’ mandarin ‘East India SRA 414’ mandarin ‘Malvasio SRA 115’ mandarin ‘Cleópatra’ mandarin × P. trifolata ‘Rubidoux’ ‘C-54-4-4 SRA 337’ mandarin “Rohde Red” ‘Valencia’ orange + ‘Volkamer’ lemon

189.61 205.09 190.03 175.81 189.19 169.76 165.04 167.53 164.78 165.77 167.98

C.V. (%) (P) Value

1.93 < 0.0001

ab a ab bcd abc bcd d cd d cd cd

Equatorial diameter mm

Polar diameter mm

TSS Brix°

85.08 84.33 87.83 86.04 86.83 84.77 84.21 84.32 83.13 85.06 84.91

89.98 95.59 91.82 89.54 91.90 88.56 88.25 88.87 87.52 88.32 89.08

12.43 11.22 11.33 12.94 12.44 12.44 12.47 12.65 13.79 12.67 11.82

11.05 0.4624NS

0.95 < 0.0001

ab a ab b ab b b b b b b

bcd e de ab bc bc bc bc a bc cde

6.60 < 0.0001

Acidity %

Ratio

0.66 0.64 0.65 0.69 0.68 0.75 0.71 0.81 0.74 0.82 0.71

18.86 17.77 17.77 19.22 18.39 16.64 17.55 15.96 18.83 15.58 17.10

bc c bc bc bc ab abc a abc a abc

8.76 < 0.0001

TI* kg

JY % a abc abc a ab abc abc bc a c abc

11.03 < 0.0001

46.17 48.31 47.80 47.21 48.21 46.70 46.82 45.31 48.14 43.25 42.90

abc a a a a ab ab abc a bc c

5.81 < 0.0001

2.32 2.20 2.21 2.48 2.44 2.35 2.35 2.31 2.70 2.21 2.06

bc bc bc ab ab bc bc bc a bc c

9.19 < 0.0001

Means followed by different letters in columns are significantly different by Tukey test (P < 0.05). *Kg of total soluble solids box−1 (40.8 kg). NSNot significant at 5% probability level. n = 15 fruits.

orange grafted onto ‘C-13’ “S” citrange and onto “Rohde Red” ‘Valencia’ + ‘Volkamer’ lemon, when evaluated individually (Table 4).

3.3. Fruit quality Rootstocks influenced fruit quality of ‘Valencia’ sweet orange; except for fruit equatorial diameter, all the other variables had significant differences, depending on rootstock (Table 2). The highest fruit mass was observed in fruits from trees grafted onto “Santa Cruz” ‘Rangpur’ lime, followed by trees grafted onto “CNPMF 003” ‘Rangpur’ lime and onto ‘Sunki’ mandarin × P. trifoliata ‘English’. Combinations grafted onto ‘Cleopatra’ mandarin × P. trifoliata ‘Rubidoux’ and ‘East India SRA 414’ mandarin induced low fruit mass in ‘Valencia’ sweet orange (Table 2). Plants on ‘Sunki’ mandarin × P. trifoliata ‘English’ had fruits with the highest ratio along with those from trees grafted onto other P. trifoliata hybrid rootstocks (Table 2). ‘Valencia’ sweet oranges from trees grafted onto ‘Cleópatra’ mandarin × P. trifoliata ‘Rubidoux’ and ‘C-13’ “S” citrange had the highest values of total soluble solids. These same rootstocks, along with ‘Sunki’ mandarin × P. trifoliata ‘Benecke’, induced the highest values of the technological index (Table 2).

3.5. Plant tolerance to drought 3.5.1. Visual assessment ‘Valencia’ sweet orange grafted onto 11 rootstocks showed differences related to drought tolerance measured through visual scores, both annually and also within the average period (2010–2012) (Table 5). In 2010, ‘Valencia’ sweet orange grafted onto two ‘Rangpur’ lime clones (“CNPMF 003” and “Santa Cruz”) were the most tolerant to drought, differing from other combinations (Table 5). In our 2011 assessment, combinations involving ‘Rangpur’ lime clones were equivalent to ‘Sunki’ mandarin × P. trifoliata ‘English’, ‘Sunki’ mandarin × P. trifoliata ‘Benecke’, and ‘C-13’ “S” citrange. In 2012, similar performance repeated for the mentioned rootstocks, plus the ‘East India SRA 414’ mandarin, “Rohde Red” ‘Valencia’ sweet orange + ‘Volkamer’ lemon, and ‘Cleopatra’ mandarin × P. trifoliata ‘Rubidoux’ ones (Table 5). Overall, in an average of the three assessments (2010–2012), ‘Valencia’ sweet orange grafted onto two ‘Rangpur’ lime clones showed the best drought tolerance based on visual scores. However, the combination involving ‘Valencia’ sweet orange and ‘Sunki’ mandarin × P. trifoliata ‘English’ did not differ from ‘Valencia’ sweet orange grafted onto “Santa Cruz” ‘Rangpur’ lime (Table 5), both of which has satisfactory drought tolerance.

3.4. Correlations between yield, plant size, and fruit quality Yield (kg plant−1) had a positive correlation to plant size (canopy volume), yield efficiency, fruit equatorial and polar diameter, total soluble solids, ratio, and technological index (Table 3). In general analysis (considering all rootstock combinations), the yield had a positive correlation to plant size (Table 3) whereas no correlation was found between theses variables in individual analyses, for each rootstock (Table 4). Similarly, in general analysis, a positive correlation was registered between yield and yield efficiency (Table 3). Individual analyses also revealed a positive correlation between these variables for at least eight of the 11 tested combinations (Table 4). Unlike the general analysis, a positive correlation between yield and total soluble solids was observed in individual analyses of ‘Valencia’ sweet orange grafted onto “Santa Cruz” and “CNPMF 003” ‘Rangpur’ lime, ‘Sunki’ mandarin × P. trifoliata ‘Benecke’, ‘East India SRA 414’ mandarin and “Rohde Red” ‘Valencia’ + ‘Volkamer’ lemon (Table 4). In general analysis, the correlation between plant size and yield efficiency was negative (Table 3). However, when analyzed individually, the combinations related to ‘À Peau Lisse SRA 267’, ‘East India SRA 414’, ‘Malvasio SRA 115’ and ‘C-54-4-4 SRA 337’ mandarins, ‘Cleópatra’ mandarin × P. trifoliata ‘Rubidoux’ and “Rohde Red” ‘Valencia’ + ‘Volkamer’ lemon did not correlate (Table 4). Another divergence was related to the positive correlation between plant size and fruit mass (Table 3), which was confirmed only in ‘Valencia’ sweet

3.5.2. Leaf water potential In April 2012, leaves of ‘Valencia’ sweet orange grafted onto “CNPMF 003” ‘Rangpur’ lime and ‘Sunki’ mandarin × P. trifoliata ‘Benecke’ had higher leaf water potential than those on “Rohde Red” ‘Valencia’ orange + ‘Volkamer’ lemon, ‘À Peau Lisse SRA 267’ mandarin, ‘C-54-4-4 SRA 337’ (Fig. 1), under water deficit conditions (Fig. 2). Over the course of the experiment, the soil was most water deficient in August 2012 (Fig. 2). Under those conditions, those trees grafted onto “Santa Cruz” ‘Rangpur’ lime had the highest water potential in their leaves. In August 2012, trees grafted onto “CNPMF 003” ‘Rangpur’ lime, ‘C-13’ “S” citrange, ‘Sunki’ mandarin × P. trifoliata ‘English’, ‘Sunki’ mandarin × P. trifoliata ‘Benecke’, “Rohde Red” ‘Valencia’ + ‘Volkamer’ lemon, and ‘East India SRA 414’ mandarin had intermediate water potential in ‘Valencia’ sweet orange leaves (Fig. 1). In the same season, the lowest leaf water potential was observed in trees grafted onto ‘Cleopatra’ mandarin × P. trifoliata ‘Rubidoux’, ‘À Peau Lisse SRA 267’, ‘C-54-4-4 SRA 337’, and ‘Malvasio SRA 115’ mandarins (Fig. 1). In October and December 2012, due to the gradual 400

Scientia Horticulturae 235 (2018) 397–406 < 0.0001(+) < 0.0001(+) 0.0005(+) NS ..........

reduction of soil water deficit (Fig. 2), no significant differences were observed related to water potential in ‘Valencia’ sweet orange leaves grafted onto the various rootstocks (data not shown). In 2013, there was greater homogeneity among the leaf water potential of ‘Valencia’ sweet orange trees grafted onto the 11 different rootstocks. In this case, only in the August assessment, there were statistical differences between the different scion/rootstock combinations (Fig. 1). For this assessment, ‘Valencia’ sweet orange grafted onto ‘Sunki’ mandarin × P. trifoliata ‘Benecke’ had the highest water potential values. In August 2012 and August 2013, the lowest water potential was for trees grafted onto ‘Malvasio SRA 115’ mandarin (Fig. 1). Data from an average of the four 2012 assessments showed that trees grafted onto “CNPMF 003” ‘Rangpur’ lime had the highest leaf water potential, whereas the lowest values were recorded on ‘Valencia’ sweet orange leaves grafted onto ‘À Peau Lisse SRA 267’, ‘C-54-4-4 SRA 337’ and ‘Malvasio SRA 115’ mandarins (Fig. 3). In general, as an average of the four 2013 assessments, the highest leaf water potential was observed in ‘Valencia’ sweet orange grafted onto ‘C-13’ “S” citrange. As observed in 2012, in 2013 assessments ‘Valencia’ orange grafted onto ‘Malvasio SRA 115’ mandarin showed the lowest leaf water potential values (Fig. 3). A comparison between the two drought tolerance assessment methods was carried out through a simple linear correlation regression, whereas leaf water potential was the dependent variable and the score rates were the independent variable. The regression analysis was significant between these two variables (Fig. 4). 4. Discussion The good yield performance of ‘Valencia’ sweet orange grafted onto ‘Sunki’ mandarin × P. trifoliata ‘English’ reported in our work was also reported in a similar study, wherein ‘Sunki’ mandarin × P. trifoliata ‘English’ rootstock conferred high yields, yield efficiencies, and juice ratio to ‘Valencia’ sweet orange (Chaparro-Zambrano et al., 2015). Superior performance was also reported in ‘Valencia’ sweet orange grafted onto ‘Changsha’ mandarin × P. trifoliata ‘English Large’ among 12 rootstocks in nine annual harvests in Pirassununga, Brazil (Pompeu Junior et al., 2002). In Florida, a study involving 17 rootstocks indicated that ‘Valencia’ sweet orange grafted onto ‘Changsha’ mandarin × P. trifoliata ‘English Large’ (US-852) was classified as satisfactory related to fruit production per plant (kg plant −1) in the first four harvests (Bowman et al., 2016). In another study in the same region, ‘Hamlin’ sweet orange (C. sinensis (L.) Osbeck) had good yield performance when grafted onto the same hybrid rootstock (Wutscher and Hill, 1995). In our work, ‘Valencia’ sweet orange grafted onto ‘Sunki’ mandarin × P. trifoliata ‘Benecke’ was grouped in an intermediate yield cluster. In other works, this hybrid had good performance when used as a rootstock for ‘Valencia’ sweet orange in Florida (Wutscher and Bowman, 1999) and in Brazil (Pompeu Junior et al., 2002). In another study, under high huanglongbing (HLB) incidence, high yields of ‘Valencia’ sweet orange were reported for the ‘Sunki’ mandarin × P. trifoliata ‘Flying Dragon’ hybrid (US-942) when compared to other rootstocks, such as ‘Carrizo’ citrange and ‘Cleopatra’ mandarin (Bowman et al., 2016). In that same study, plants onto C. grandis ‘African’ × P. trifoliata ‘Flying Dragon’ (US-1516) also had adequate performance and the lowest number of trees eradicated due to HLB. In another study in Sicily, similar and adequate accumulated yields were reported in ‘Tarocco’ sweet orange grafted onto three different hybrids between P. trifoliata and C. latipes (Swing.) Tan. and onto ‘Swingle’ citrumelo, along six harvests. In Sardinia, adequate performance of ‘Washington Navel’ sweet orange was reported in plants grafted onto two hybrids involving these progenitors and also onto ‘Swingle’ citrumelo (Reforgiato Recupero et al., 2009). High yields of ‘Valencia’ sweet orange on ‘Rangpur’ lime when compared to those plants on ‘Sunki’ mandarin and P. trifoliata

2

1

Yield (kg tree−1) in 2009, 2010, 2011, 2012, 2013 and 2014 harvests. Canopy volume (m3), yield efficiency (YE) kg m3 measured in 2010, 2011, 2012, 2013 and 2014. 3 Mass (g), equatorial diameter (mm), polar diameter (mm), total soluble solids (TSS), acidity (%), ratio, juice yield (% JY) and technological index (TI) measured in 2010, 2011, 2012 and 2013. * P < 0.01 values indicate correlation at 1% probability level, P < 0.05 and > 0.01 values indicate correlation at 5% probability level. ** Positive signs (+) indicates positive correlation and negative signs (−) indicates negative correlation between variables. *** Not significant at 5% probability level.

< 0.0001(−) 0.0006(−) 0.0387(−) .......... < 0.0001(+) .......... ..........

< 0.0001(+) < 0.0001(−) ..........

< 0.0001(−) NS < 0.0001(−) ..........

0.0016(−)

0.0009(+)

0.0120(+) NS < 0.0001(+) < 0.0001(−) 0.0006(−) < 0.0001(−) 0.0003(−) < 0.0001(−) < 0.0001(+) NS < 0.0001(+) 0.0159(+) < 0.0001(+) NS 0.0013(+) NS NS NS < 0.0001(−) < 0.0001(−) < 0.0001(+) NS < 0.0001(+) < 0.0001(−) 0.0289(−) ..........

Yield1 Canopy volume2 YE3 Mass3 Equatorial3 diameter Polar3 diameter TSS3 Acidity3 Ratio3 RS3 IT3

0.0004*(+) ..........

< 0.0001(+)** < 0.0001(−)** ..........

NS*** < 0.0001(+) < 0.0001(−) ..........

< 0.0001(+) < 0.0001(+) 0.0041(−) < 0.0001(+) ..........

0.0006(+) < 0.0001(+) 0.0002(−) < 0.0001(+) < 0.0001(+)

Acidity3 TSS3 Polar diameter3 Equatorial diameter3 Mass3 YE3 Canopy volume2 Yield1 Variable

Table 3 Spearman correlation coefficient between variables related to yield, tree growth and fruit quality of ‘Valencia’ sweet orange grafted onto eleven rootstocks. Colombia, Brazil.

Ratio3

JY3

TI3

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Table 4 Spearman correlation coefficient between yield and canopy volume, yield and yield efficiency (YE), yield and total soluble solids (TSS), yield and ratio, canopy volume and yield efficiency (YE) and between canopy volume and fruit mass (g) of ‘Valencia’ sweet orange grafted onto eleven rootstocks. Colombia, Brazil. Rootstock

Yield1 × canopy volume2

Yield1 × YE2

Yield1 × TSS3

Yield1 × ratio3

Canopy volume2 × YE2

Canopy volume2 × mass3

‘Sunki’ mandarin × P. trifoliata ‘English’ “Santa Cruz” ‘Rangpur’ lime “CNPMF 003” ‘Rangpur’ lime ‘C-13’ “S” citrange ‘Sunki’ mandarin × P. trifoliata ‘Benecke’ ‘À Peau Lisse SRA 267’ mandarin ‘East India SRA 414’ mandarin ‘Malvasio SRA 115’ mandarin ‘Cleópatra’ mandarin × P. trifolata ‘Rubidoux’ ‘C-54-4-4 SRA 337’ mandarin “Rohde Red” ‘Valencia’ orange + ‘Volkamer’ lemon

NS*** NS NS NS NS NS NS NS NS NS NS

NS NS 0.0039(+) 0.0337(+) NS 0.0002(+) 0.0054(+) 0.0087(+) 0.0019(+) 0.0003(+) 0.0018(+)

NS 0.0017*(+) 0.0258(+) NS 0.0003(+) NS 0.0341(+) NS NS NS 0.0363(+)

NS 0.0102(+)** NS 0.0074(+) 0.0006(+) NS NS NS 0.0034(+) NS NS

0.0038(−) 0.0007(−) 0.0164(−) 0.0487(−) 0.0140(−) NS NS NS NS NS NS

NS NS NS 0.0114(+) NS NS NS NS NS NS 0.0479(+)

Yield (kg panta−1) in 2009, 2010, 2011, 2012, 2013 and 2014 harvests. Canopy volume (m3), yield efficiency (YE) kg m3, in 2010, 2011, 2012, 2013 and 2014. 3 Total soluble solids (TSS), ratio and fruit mass (g) measured in 2010, 2011, 2012 and 2013. * P < 0.01 values indicate correlation at 1% probability level, P < 0.05 and > 0.01 values indicate correlation at 5% probability level. ** Positive signs (+) indicates positive correlation and negative signs (−) indicates negative correlation between variables. *** Not significant at 5% probability level. 1 2

yield per area during the first harvests in high-density citrus planting, cost reduction due to the replanting of trees eradicated by disease is another benefit attributed to dwarfing rootstocks (Stuchi and Girardi, 2011). Overall, high-density citrus commercial orchards, besides leading to early fruit bearing, can increase economic viability, mainly because of reduced disease management costs (Castle et al., 2010). High-density plantings of ‘Pera’ sweet orange [Citrus sinensis (L.) Osbeck] grafted onto ‘Cleopatra’, ‘Valencia’ sweet orange grafted onto P. trifoliata ‘Limeira’, and ‘Hamlin’ sweet orange grafted onto ‘Rangpur’ lime in Bebedouro, Brazil, provided an increase of up to 50% in the eight first harvests (Stuchi and Girardi, 2011). Some rootstock hybrids or selections may show different performances in a given environment. This fact is confirmed in our work because the growth and canopy volume of ‘Valencia’ sweet orange trees grafted onto two hybrids from different crosses involving the same progenitors (‘Sunki’ mandarin × P. trifoliata) had different responses (Table 1). This result may be important to orchard design strategies, as already commented. Differences in plant size and general performance of sweet orange on distinct ‘Sunki’ mandarin × P. trifoliata hybrids have also been reported in a previous study (Schinor et al., 2013). ‘Navelina’ sweet orange [C. sinensis (L.) Osb.] grafted onto ‘FA-517’ [Citrus nobilis Lour. × P. trifoliata (L.) Raf.] and ‘FA-418’ (‘Troyer’ citrange × C. deliciosa Ten.) dwarfing rootstocks presented good performance compared to ‘Carrizo’ citrange [C. sinensis (L.) Osb. × P. trifoliata (L.) Raf.]

rootstocks, as found in our study, have also been reported in by Bordignon et al. (2003). In that same study, plants of ‘Valencia’ sweet orange had an early bearing when grafted onto hybrids between P. trifoliata × ‘Sunki’ mandarin and ‘Sunki’ mandarin × P. trifoliata. In citrus, after the anthesis, fruit abscission occurs mainly due to faulty fruit formation and high temperatures during the season (Davies and Albrigo, 1994). Temperatures above 35 °C may contribute to continuity abscission fruit for two to three months, after the first abscission phase (Ben Mechlia and Carroll, 1989). Results from our work suggest that periods with high temperatures associated with elevated soil water deficit may have significantly affected fruit yield. We observed an increasing average yield from 2009 through 2012, which is expected because it followed plant growth (Table 1). On the other hand, decreasing yields were recorded in 2013 and 2014. In our opinion, this fact cannot be characterized as alternate bearing, but caused by the extreme soil water deficiency recorded in those years (Fig. 2). Our study also revealed significant differences among plant canopy volume of ‘Valencia’ sweet orange grafted onto different rootstocks. In our case, these differences could be as high as 100% increase depending on the rootstock (Table 1). Plant growth and final canopy volume directly affect orchard design and plant spacing. In recent years, highdensity planting has become an essential practice for economic viability to the current citrus industry. In addition to financial returns anticipation, provided by higher

Table 5 Drought tolerance assessment by visual scores in leaves of ‘Valencia’ sweet orange grafted onto eleven rootstocks from 2010 to 2012. Colombia. Brazil. Rootestock

2010

2011

2012

2010–2012**

“CNPMF 003” ‘Rangpur’ lime “Santa Cruz” ‘Rangpur’ lime ‘Sunki’ mandarin × P. trifoliata ‘English’ ‘Sunki’ mandarin × P. trifoliata ‘Benecke’ ‘C-13’ “S” citrange ‘East India SRA 414’ mandarin “Rohde Red” ‘Valencia’ orange + ‘Volkamer’ lemon ‘À Peau Lisse SRA 267’ mandarin ‘Cleópatra’ mandarin × P. trifolata ‘Rubidoux’ ‘Malvasio SRA 115’ mandarin ‘C-54-4-4 SRA 337’ mandarin C.V. (%) (P) Value

2.47 a 2.04 a 1.33 b 1.17 b 1.07 b 1.00 b 1.00 b 1.00 b 1.00 b 1.13 b 1.00 b 76.98 < 0.0001

2.80 a 2.87 a 2.27 abc 2.42 ab 1.93 abcd 1.50 bcd 1.28 d 1.72 bcd 1.43 cd 1.33 d 1.27 d 28.38 < 0.0001

2.87 a 2.64 a 2.67 a 2.63 a 2.10 ab 1.93 ab 2.10 ab 1.60 bc 1.87 ab 1.60 bc 1.20 c 21.30 < 0.0001

2.71 a 2.52 ab 2.09 bc 2.07 c 1.70 cd 1.48 de 1.46 de 1.44 de 1.43 de 1.36 de 1.16 e 31.47 < 0.0001

Scores close to 1 indicate lower drought tolerance. Scores close to 3 indicate higher drought tolerance. **Average of three assessments (2010, 2011 and 2012). Means followed by different letters in columns are significantly different by Tukey test (P < 0.05).

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Fig. 1. Leaf water potential (ψf) of ‘Valencia’ sweet orange grafted onto eleven rootstocks. Colombia. Brazil. Megapascal mean values (MPa), related to April 2012, August 2012 and August 2013 assessments. “CNPMF 003” ‘Rangpur’ lime (1), ‘C-13’ “S” citrange (2), “Santa Cruz” ‘Rangpur’ lime (3), ‘Sunki’ mandarin × P. trifoliata ‘English’ (4), ‘Sunki’ mandarin × P. trifoliata ‘Benecke’ (5), “Rohde Red” ‘Valencia’ orange + ‘Volkamer’ lemon (6), ‘Cleopatra’ mandarin × P. trifolata ‘Rubidoux’ (7), ‘East India SRA 414’ mandarin (8), ‘À Peau Lisse SRA 267’ mandarin (9), ‘C-54-4-4 SRA 337’ (10) mandarin, ‘Malvasio SRA 115’ mandarin (11). Different letters among columns are significantly different by Tukey test (P < 0.05). Bars indicate the standard error of the mean.

‘English’, and ‘Cleopatra’ mandarin × P. trifoliata ‘Rubidoux’. The latter rootstock also induced the highest technological index in fruits (Table 2). It is important to point out that these results indicate a separate and superior group of rootstocks for internal fruit quality, as compared to other rootstocks traditionally used in the Brazilian citrus industry (e.g., ‘Rangpur’ lime selections). All these superior rootstocks are hybrids involving P. trifoliata as one progenitor. The high fruit quality of ‘Henderson’ grapefruit (C. paradisi Macfad.) has also been reported in plants grafted onto ‘Troyer’ citrange (another P. trifoliata hybrid) (Yeşiloğlu et al., 2014) and in ‘Valencia’ sweet orange on ‘Swingle’ citrumelo [Citrus paradisi Macfad. × Poncirus trifoliata (L.) Raf.] (Zekri, 2000). Besides inducing high fruit quality in ‘Valencia’ sweet orange (Table 2), ‘C-13’ “S” citrange rootstock also reduced canopy volume and resulted in the highest yield efficient plants per m3 scion (Table 1). Such characteristics conferred to the canopy have already been reported in combinations related to ‘Valencia’ “Late” sweet orange and other citranges (Yildiz et al., 2013), but not assembled in the same citrange selection, as is the case for the combination involving ‘C-13’ “S” presented here. Previous studies reported the direct relationship (positive correlation) between climatic factors (air temperature and water precipitation) and fruit ratio in ‘Valencia’ and ‘Natal’ sweet oranges (Volpe et al.,

regarding fruit quality and yield efficiency, suggesting good fitness to high-density planting (Forner-Giner et al., 2014). High yield efficiency reported in combinations involving dwarfing rootstocks might be related to translocation deficiency of carbohydrates from the scion to rootstock, in the grafting zone, resulting in higher carbohydrate availability in the scion (Martínez-Alcántara et al., 2013). Citrus fruit quality can be measured as external characteristics (fruit mass and shape) or internal characteristics [juice quality, total soluble solids (TSS), total acids (TA), and TSS/TA ratio]. In our work, rootstock significantly influenced fruit quality of ‘Valencia’ sweet orange. Regarding external characteristics, “Santa Cruz” ‘Rangpur’ lime induced the highest fruit mass followed by combinations with “CNPMF 003” ‘Rangpur’ lime and ‘Sunki’ mandarin × P. trifoliata ‘English’. Fruit size and fruit mass differences have also been reported in ‘Shatangju’ mandarin (C. reticulata Blanco) grafted onto ‘Canton’ lemon (C. limonia Osbeck) and P. trifoliata. Authors have suggested that these differences could be associated with different levels of auxin and abscisic acid in fruits, induced by the rootstocks (Liu et al., 2015). Several attributes comprise internal fruit quality, such as total soluble solids, total acids, ratio, juice yield, and technological index. Our report indicates that at least three different rootstocks induced superior quality in fruits of ‘Valencia’ sweet orange, expressed as TSS/TA ratio. These rootstocks are ‘C-13’ “S” citrange, ‘Sunki’ mandarin × P. trifoliata

Fig. 2. Extract of climatic water balance from 2009 to 2014 calculated by spreadsheet Thornthwaite and Mather (Rolim et al., 1998). Colombia. Brazil. Available Water Capacity = 100 mm.

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Fig. 3. Leaf water potential (ψf) of ‘Valencia’ sweet orange grafted onto eleven rootstocks. Colombia. Brazil. Megapascal mean values (MPa), related to April, August, October, November (2012 and 2013) assessments. “CNPMF 003” ‘Rangpur’ lime (1), ‘C-13’ “S” citrange (2), “Santa Cruz” ‘Rangpur’ lime (3), ‘Sunki’ mandarin × P. trifoliata ‘English’ (4), ‘Sunki’ mandarin × P. trifoliata ‘Benecke’ (5), “Rohde Red” ‘Valencia’ orange + ‘Volkamer’ lemon (6), ‘Cleopatra’ mandarin × P. trifolata ‘Rubidoux’ (7), ‘East India SRA 414’ mandarin (8), ‘À Peau Lisse SRA 267’ mandarin (9), ‘C-54-4-4 SRA 337’ (10) mandarin, ‘Malvasio SRA 115’ mandarin (11). Different letters between columns are significantly different by Tukey test (P < 0.05). Bars indicate the standard error of the mean.

tolerant (Pompeu Junior, 1991). Moreover, “CNPMF 003” and “Santa Cruz” ‘Rangpur’ lime selections were used as drought-tolerant controls. ‘Tahiti’ acid lime trees [C. latifolia (Yu. Tanaka) Tanaka] grafted onto ‘Rangpur’ lime, and ‘Volkamer’ lemon were also more drought-tolerant when evaluated by visual scores in comparison with other rootstocks (Espinoza Núñez, 2010). Besides being an efficient method to evaluate drought tolerance in citrus, visual assessment, by scores, has been adequate to evaluate external fruit quality in ‘Pink Lady’ apple (O’Connell and Goodwin, 2007), to estimate chilling injuries in ‘Fortune’ mandarin fruits (Citrus Clementina hort. ex Tanaka × Citrus reticulata Blanco) (Sanchez-Ballesta et al., 2004), and to evaluate post-harvest external damage in ‘Navelina’ sweet orange (Alférez et al., 2003). Drought tolerance evaluation through visual assessment has been an adequate method to estimate plant drought tolerance. Good relationships between this method and drought tolerance evaluation through leaf water potential have been reported (Bremer Neto, 2012). In other crops, such as in rice (Oryza sativa L.), visual scores related to drought tolerance based on leaf wilting/drying were highly correlated with leaf water potential maintenance (O’Toole and Moya, 1978). In another study, with 27 rice cultivars, visual scores were correlated with leaf area reduction and with plant dry mass (Cabuslay et al., 2002). In our study, drought evaluation through visual assessment data had a significant linear relationship with the leaf water potential drought tolerance estimation method (Fig. 4), confirming that this method is adequate and reliable for the estimation of plant drought-tolerance in citrus. Based on visual scores, ‘Valencia’ sweet orange grafted onto ‘Sunki’ mandarin × P. trifoliata ‘English’ had good drought-tolerance compared with “CNPMF 003” and “Santa Cruz” ‘Rangpur’ limes (drought-tolerance control rootstocks). ‘Rangpur’ lime is considered drought-tolerant because it has deep root development, great root water absorption, and high hydraulic conductivity (Syvertsen, 1981; Ribeiro et al., 2014). These attributes are considered drought resistance mechanisms (Taiz and Zeiger, 2004). Other characteristics related to drought tolerance, such as elastic adjustment, osmotic adjustment, and oxidative stress control were attributed to rootstocks ‘Rangpur’ lime and ‘Sunki’ mandarin during the lower soil water available season (Gonçalves et al., 2016). Despite the poor performance of plants grafted onto ‘Malvasio SRA 115’ rootstock regarding leaf water potential, when compared to the “CNPMF 003” ‘Rangpur’ lime and ‘C-13’ “S” citrange, ‘Valencia’ sweet orange grafted onto these three rootstocks did not differ from each other regarding scion volume (Table 1). In our study, ‘Malvasio SRA 115’ mandarin may present dehydration retardation mechanisms,

Fig. 4. Linear regression. Leaf water potential (ψf) of ‘Valencia’ sweet orange grafted onto eleven rootstocks from 2012 and 2013 depending on drought tolerance visual score in 2010 through 2012. Colombia. Brazil. ** regression is statistically significant (P < 0.01).

2002; Kimball, 1984). On the other hand, decreases in fruit acidity might be due to an increase in fruit size and water content (Kimball, 1984), resulting in a negative correlation between fruit equatorial diameter and total acidity, and fruit polar diameter and total acidity (Table 3). However, moderate water stress during ripening season might positively influence total soluble solids and acidity concentration in sweet orange, in some cases, enhancing fruit quality (Aguado et al., 2012). In our study, significant correlations were registered in fruit yield × fruit yield efficiency, fruit mass × equatorial fruit diameter, and acidity × ratio (Table 3), confirming previous results related the same fruits variables in ‘Lane Late’ sweet orange grafted onto different rootstocks (Legua et al., 2011). We found that interpretations about the correlation between the variables might depend on the data analysis methods used. In this case, we can conclude that different combinations between scion and rootstock can originate different interactions between variables analyzed here, related to plant size, yield, and fruit quality. Based on general and individual correlations analyses, we can affirm that data indicate a positive correlation between yield efficiency and total soluble solids, negative correlation between fruit mass and total soluble solids and positive correlation between total soluble solids and technological index. The best performance was related to drought tolerance, although visual assessment in combinations involving ‘Rangpur’ lime selections were already expected, because ‘Rangpur’ lime is considered drought404

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probably associated with unrestricted water absorption (Taiz and Zeiger, 2004). During the season of greater soil water availability, plants grafted onto ‘Malvasio SRA 115’ would present unrestricted water absorption, providing adequate vegetative growth. On the other hand, during periods of soil water deficiency and high temperatures, trees on this rootstock would show faster dehydration comparing with ‘Rangpur’ lime, due to an increase in transpiration. Greater transpiration of ‘Valencia’ sweet orange trees grafted onto ‘Rangpur’ lime was influenced by the increase of scion leaf density when compared to those on ‘Swingle’ citrumelo (Vellame et al., 2012). Previous studies have reported a reduction in canopy vigor on dwarfing rootstocks due to scion’s lower water potential, probably because of a more difficult water transport from roots to scion (FornerGiner et al., 2014; Olien and Lakso, 1986). In contrast, in our study, leaf water potential in ‘Valencia’ sweet orange trees grafted onto ‘C-13’ “S” citrange did not significantly differ from plant values in “CNPMF 03” and “Santa Cruz” ‘Rangpur’ lime clones (Figs. 1 and 3), although plants grafted onto “Santa Cruz” ‘Rangpur’ lime had higher canopy volume (at least 3 m3 more) than those grafted onto ‘C-13’ “S” citrange (Table 1). Lower hydraulic conductivity was reported in plants grafted onto two dwarfing rootstocks compared with those onto ‘Carrizo’ citrange. According to this study, when used as rootstocks for ‘Navelina’ sweet orange, a high concentration of xylem vessels with smaller diameters were associated with these dwarfing rootstocks, in comparison with ‘Carrizo’ citrange (Forner-Giner et al., 2014). Similar results were also reported in peach dwarfing rootstock (Tombesi et al., 2010). In our study, high fruit yields were recorded in ‘Valencia’ sweet orange trees grafted onto ‘Sunki’ mandarin × P. trifoliata ‘English’, which was similar to those values in plants onto “Santa Cruz” ‘Rangpur’ lime. Plants grafted onto ‘C-13’ “S” citrange and ‘Cleopatra’ mandarin × P. trifoliata ‘Rubidoux’ had small canopy volume and high yield efficiency, leading to possible high-density plantings. These rootstocks also induced superior internal fruit quality. On the other hand, plants grafted onto ‘C-13’ “S” citrange, ‘Sunki’ mandarin × P. trifoliata ‘Benecke’ and ‘Sunki’ mandarin × P. trifoliata ‘English’ had good performance regarding drought tolerance when compared to ‘Rangpur’ lime clones, evaluated by leaf water potential and visual scores. Therefore, according to our study, ‘Sunki’ mandarin × P. trifoliata ‘English’ and ‘C-13’ “S” citrange had potential to be used as rootstocks for ‘Valencia’ sweet orange in rainfed conditions, as an alternative to the common used ‘Rangpur’ lime.

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