Impaginato 141 Adv. Hort. Sci., 2023 37(2): 141­148 DOI: 10.36253/ahsc­14173 Superior sweet oranges for varietal diversification of tropical rainfed orchards A.V. Teodoro 1 (*), H.W. Lemos de Carvalho 1, I. de Barros 2, L. Marques de Carvalho 1, E.A. Girardi 3, O. Sampaio Passos 3, W. dos Santos Soares Filho 3 1 Embrapa Tabuleiros Costeiros, Avenida Beira Mar, 3250, Bairro Jardins, Aracaju, 49025‐040 Sergipe, Brazil. 2 Embrapa Gado de Leite, Rua Eugênio do Nascimento, 610, 36038‐330 Juiz de Fora, Minas Gerais, Brazil. 3 Embrapa Mandioca e Fruticultura, Rua Embrapa sn, 44380‐000 Cruz das Almas, Bahia, Brazil. Key words: Alternate bearing, Citrus sinensis, fruit quality, scions, vegetative growth, water deficit, yield. Abstract: Citrus orchards in northeastern Brazil are mostly rainfed and com­ prised basically of ‘Pera CNPMF D­6’ sweet orange budded on ‘Rangpur’ lime, for the drought tolerance and productivity imparted by this rootstock. Therefore, the selection of new varieties is needed to broaden the genetic basis of citrus cultivated in this region. Accordingly, this study compared vegetative, productive, and fruit quality traits of eight sweet orange scions grafted on ‘Rangpur’ lime over eleven years under the tropical rainfed conditions of north­ eastern Brazil. ‘Kona’ trees excelled in yield performance associated with bulk canopy, precocity, sweet fruit with intermediate acidity, and high vitamin C contents in spite of proneness to alternate yields and low ratio (maturity index). ‘Valencia Montemorelos’ and ‘Rubi’ trees, in turn, had high yield perfor­ mances coupled with intermediate canopies, sweet fruit, intermediate acidity (‘Rubi’) and vitamin C contents, low propensity for yield fluctuation (‘Valencia Montemorelos’), and high precocity (‘Rubi’), albeit low ratio. Overall, our results emphasize ‘Kona,’ ‘Valencia Montemorelos,’ and ‘Rubi’ as superior sweet orange varieties for diversification of tropical rainfed orchards for their outstanding yield performance and good fruit quality. 1. Introduction Brazil is the largest producer of sweet oranges [Citrus sinensis (L.) Osbeck] worldwide, with 578,057 ha and 16.21 million tons of fruit har­ vested in 2021 (FAO, 2021). The country is also the world’s top exporter of orange juice. Most orchards are rainfed, and the southeast and north­ east regions are the main producers nationwide, with 421,171 ha and 98,475 ha, respectively. However, the yields in the northeast (11.40 t·ha­1) (*) Corresponding author: adenir.teodoro@embrapa.br Citation: TEODORO A.V., LEMOS DE CARVALHO H.W., DE BARROS I., MARQUES DE CARVALHO L., GIRARDI E.A., SAMPAIO PASSOS O., DOS SANTOS SOARES FILHO W., 2023 ­ Superior sweet oranges for varietal diversification of tropical rainfed orchards. ­ Adv. Hort. Sci., 37(2): 141­148. Copyright: © 2023 Teodoro A.V., Lemos de Carvalho H.W., de Barros I., Marques de Carvalho L., Girardi E.A., Sampaio Passos O., dos Santos Soares Filho W. This is an open access, peer reviewed article published by Firenze University Press (http://www.fupress.net/index.php/ahs/) and distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability Statement: All relevant data are within the paper and its Supporting Information files. Competing Interests: The authors declare no competing interests. Received for publication 14 January 2023 Accepted for publication 21 March 2023 AHS Advances in Horticultural Science https://doi.org/10.36253/ahsc-14173 http://www.fupress.net/index.php/ahs/ http://creativecommons.org/licenses/by/4.0/ http://creativecommons.org/licenses/by/4.0/ http://creativecommons.org/licenses/by/4.0/ Adv. Hort. Sci., 2023 37(2): 141­148 142 are only a third of those in the southeast (IBGE, 2019). Lower yields in northeastern Brazil stem mainly from soils with fertility restrictions and hardsetting layers that impair drainage and root development in addition to water deficits due to irregular rainfall dis­ tribution, low technology adoption, improper man­ agement practices, and aging plants (Gomes et al., 2017; Carvalho et al., 2020; Martins et al., 2020). Despite water deficit negatively affecting citrus yields, citriculture in Brazil is predominantly rainfed (Carvalho et al., 2019 a, 2020, 2022). Water stress linked to climate change is predicted to increase and affect the citrus industry worldwide (Fares et al., 2017). In addition to these constraints, most citrus orchards in this region comprise ‘Pera CNPMF D­6’ sweet orange (referred to as ‘Pera’) budded on ‘Rangpur’ lime (C. limonia Osbeck), which is a graft­ compatible rootstock that confers good tolerance to drought, quality to fruits, and yield to scions (Carvalho et al., 2020). ‘Pera’ has a medium­sized canopy and is classified as a mid­season maturating variety beginning in July with fruit suited for both in natura consumption and juice production (Carvalho et al., 2019 b). However, broadening the genetic diversity of scions could increase the much­needed fruit yield and quality to enhance the competitiveness of farms in this region. Accordingly, in 2008, the Brazilian Agricultural Research Corporation (Embrapa) estab­ lished a comprehensive research project aimed at varietal diversification with scion­rootstock combina­ tions for rainfed citrus orchards in the coastal table­ lands of northeastern Brazil. As a result, new combi­ nations of sweet oranges and rootstocks have been selected for cultivation in this area (Carvalho et al., 2019 b, 2020, 2022). Herein, we recommend new varieties of sweet oranges for the diversification of tropical rainfed orchards. To this end, we conducted comparative vegetative, productive, and fruit quality trait assessments among eight sweet orange scions grafted on ‘Rangpur’ lime over eleven years in Brazil’s northeastern region. 2. Materials and Methods Site description and experimental design The study was conducted from 2008 to 2019 at the experimental station of Embrapa in Umbaúba (11° 22’ 37’’ S, 37° 40’’ 26’’ W; 109 m a.s.l.), Sergipe State, in the coastal tablelands of northeastern Brazil. The study site soil is an Haplic Acrisol (Ultisol), which is a reddish­yellow acid soil with medium texture, a clay­rich B horizon (Kaolinite). According to soil ana­ lyses at 0­20 cm depth, the pH is 6.72, phosphorus 13.5 mg⋅dm3, organic matter 21.2 g.kg1, potassium 0.23 g.kg1, Calcium 2.22 g.kg1, Magnesium 0.86 g.kg1, and base saturation (74%). The climate is classified as “As” according to Köppen­Geiger, with a rainy period from May to September. Rainfall was recorded over the study period, with an annual mean of 1309 (±275) mm. The yearly rainfall and potential evapo­ transpiration patterns over the study period are shown in figure 1 a. The experimental orchard consisted of eight sweet orange scions grafted onto ‘Rangpur’ lime in a randomized complete block design, with three repli­ cates and three trees per plot. The orchard was planted at a density of 416 plants ha­1 (6.0×4.0 m) under rainfed conditions, but plants received 6 l of water weekly in the driest months. The orchard was annually fertilized according to the recommendation for sweet oranges in this region (Carvalho et al., 2022). Pest and weed control treatments with regis­ tered pesticides as well as pruning were also conduc­ ted whenever necessary. The orchard was fertilized twice a yer based on soil analysis and soil acidity was corrected by the application of dolomitic limestone. The scions were ‘Kona’, ‘Rubi’, ‘Valencia Monte­ morelos’, ‘Pera’, ‘Natal CNPMF­112’, ‘Sukkari’, ‘Lima Verde’ and ‘Lima’, and were obtained from the Embrapa Mandioca e Fruticultura breeding program. These varieties hold potential for diversifying Fig. 1 ­ Water balance measured by the difference between rain­ fall and potential evapotranspiration (PET) (a) and box­ plot chart of citrus yield for all observations during the experimental period (b) (2008­2019). Teodoro et al. ‐ Superior sweet oranges 143 orchards in the study region that are dominated by ‘Pera’ sweet orange, therefore their agronomical per­ formances under rainfed field conditions were assessed. Vegetative performance and fruit yields Vegetative growth of scions was evaluated in 8­ year­old trees in 2016 by recording plant height (PH, in m), rootstock (RD, in m) and scion diameters (SD, in m), and by estimating canopy volume (CV, in m3) as per Zekri (2000). Productive performance was assessed by fruit yield (FY, in t·ha­1) from the first harvest in 2011 to 2019, and yield efficiency (YE, in kg·m­3) was estimat­ ed in 2016 by the quotient between per plant fruit production and canopy volume. The alternate bear­ ing index (ABI) was estimated using FY from 2011 to 2019 using the following formula (Monselise and Goldschmidt, 1982): |Yi­Yi­1| ABI= ∑n (i=2) (Yi+1 +Yi­1 ) Equation (1) n­1 where n denotes years and Yi is the yield in year i. Precocity (Prec., in %) estimates considered the ratio between FY in the first two harvests and the cumula­ tive yield (CY; 2011 to 2019). Fruit quality The quality was appraised in nine randomly cho­ sen fruits per plant from the 2015 and 2016 harvests as follows: fruit weight (FW, in g·fruit­1), diameter (FD, in mm), and height (FH, in mm), as well as rind thickness (RT, in mm) as measured by a caliper, juice content (JC, in g·100 g­1 of fruit mass), total titratable acidity (TTA) was measured with 0.1 mol L­1 NaOH as titrant and given in g of citric acid per 100 mL of juice, total soluble solids (TSS, in °Brix) using a refrac­ tometer, and vitamin C content (Vit. C, in mg·100 mL­ 1 of juice) as measured by the oxidation­reduction volumetric technique using potassium iodate solu­ tion. The ratio, or maturity index, was estimated as the quotient between TSS and TTA. All measure­ ments followed the methods described by França et al. (2016). Statistical procedures Data were subjected to ANOVA, and means were grouped by Scott­Knott analysis. Multivariate analy­ ses were also performed using XLSTAT to identify homogenous groups of scions, considering only the variables that were significant in univariate analyses. Briefly, a principal component analysis (PCA) was used to shorten the dataset into synthetic and uncor­ related variables, that is, the first principal compo­ nent (Carvalho et al., 2019 a). Afterwards, the scions were grouped by agglomerative hierarchical cluster­ ing analysis (AHC) applied to the PCA scores that complied with the Kaiser criterion, that is, those whose eigenvalues were ≥1.0. Euclidean distance was used as a measure of dissimilarity, and Ward’s mini­ mum variance was used to identify clusters. The automatic truncation option was used for cluster splitting. This approach creates homogenous groups based on the largest decrease in Shannon’s entropy between a node and the next one. The resulting clus­ ters were interpreted using PCA results and put into perspective with the results of univariate analyses of variance (Carvalho et al., 2019 a). 3. Results Vegetative performance PH, RD, SD, and RD/SD girth ratio were not influ­ enced by scions (data not shown, p < 0.05). Although not significantly different, PH varied from 2.5 m (‘Lima’) to 3.5 m (‘Kona’), and RD/SD girth ratio from 1.19 (‘Valencia Montemorelos’) to 1.68 (‘Lima’). However, ‘Kona’ trees were characterized by the largest CVs (26.3 m3); ‘Valencia Montemorelos’ (19.0 m3), ‘Rubi’ (18.5 m3), and ‘Sukkari’ (17.1 m3) had intermediate values, while ‘Pera’ (15.5 m3), ‘Lima Verde’ (15.1 m3), ‘Natal CNPMF­112’ (14.3 m3), and ‘Lima’ (11.4 m3) presented the smallest canopy vol­ umes (p<0.0001). Fruit yields The annual water balance over the experimental period was predominantly negative, reaching deficits of 586 and 543 mm in the driest years of 2012 and 2016, respectively (Fig. 1 a). Considering yield perfor­ mance, the production peak of sweet oranges was generally achieved in the fifth harvest (2015), decreased until 2017, and stabilized thereafter (Fig. 1 b, Table 1). ‘Kona’ trees exhibited the highest mean yields over nine years, followed by ‘Valencia Montemorelos’ and ‘Rubi’. ‘Pera’ which is the main sweet orange grown in the study region, had inter­ mediate yields while ‘Lima’ and ‘Lima Verde’ were the least productive (Table 1). Except for ‘Lima Verde’ with the lowest values, all varieties had similar yield efficiencies. ‘Lima Verde’, Natal CNPMF­112’, Adv. Hort. Sci., 2023 37(2): 141­148 144 ‘Pera’, ‘Sukkari’ and ‘Valencia Montemorelos’ were less prone to alternate bearing. ‘Rubi’ appeared to have the highest precocity (Prec.) for the ratio between the first two harvests and the CY. However, ‘Kona’ and ‘Rubi’ presented the highest absolute yields in 2011­2012 with more than 30 t·ha­1 (Table 1). Fruit quality Regarding fruit quality, ‘Lima’ had a smaller fruit than the other scions. ‘Rubi’ fruit had the thickest rind in contrast to ‘Lima Verde’, which had the thinnest. Fruit of ‘Natal CNPMF­112’ and ‘Valencia Montemorelos’ showed the highest citric acid con­ tent, followed by those of ‘Kona’, while ‘Lima’, ‘Lima Verde’ and ‘Sukkari’ exhibited the least acid fruit. ‘Kona’, ‘Lima’, ‘Natal CNPMF­112’, ‘Rubi’, ‘Sukkari’ and ‘Valencia Montemorelos’ produced sweeter fruit than the remaining scion varieties (Table 2). Additionally, ‘Kona’ and ‘Lima’ had the highest vita­ Table 2 ­ Attributes of fruit quality of eight sweet orange varieties budded on ‘Rangpur’ lime (Average 2015­2016) z Means in the same column followed by the same letter are not significantly different according to the Scott­Knott analysis (p<0.05). TTA= Total titratable acidity; TSS = Total soluble solids. Table 1 ­ Yield performance of eight sweet orange varieties budded on ‘Rangpur’ lime (2008­2019) z Means in the same column followed by the same letter are not significantly different according to the Scott­Knott analysis (p<0.05). y Yield efficiency; x Alternate Bearing Index; w Precocity. Fruit yield (t·ha­1) YEy ABIx Prec.w (%)2011 2012 2013 2014 2015 2016 2017 2018 2019 Mean Kona 12.1 c z 23.5 a 11.7 b 19.1 b 72.5 a 46.4 a 14.0 b 29.8 a 33.2 a 29.2 a 4.27 a 0.33 c 13.6 c Lima 4.3 f 4.7 e 10.1 b 12.0 d 34.4 c 17.6 d 7.4 d 13.8 d 13.9 d 13.1 e 3.73 a 0.27 b 7.6 e Lima Verde 4.2 f 4.8 e 12.2 b 11.2 d 31.8 c 17.5 d 8.9 d 12.6 d 10.9 d 12.7 e 2.79 b 0.24 a 7.9 e Natal CNPMF­112 13.5 b 7.6 d 10.3 b 15.2 c 20.1 d 24.8 c 11.6 c 13.2 d 23.2 b 15.5 d 4.26 a 0.20 a 15.2 b Pera CNPMF D­6 8.0 d 15.4 b 13.8 a 15.9 c 39.4 b 25.4 c 15.5 a 14.0 d 12.8 d 17.8 c 3.98 a 0.19 a 14.6 b Rubi 11.6 c 23.0 a 15.6 a 20.8 a 40.7 b 26.8 c 12.7 c 24.7 b 15.2 d 21.2 b 3.53 a 0.26 b 18.1 a Sukkari 6.5 e 11.8 c 12.2 b 13.3 d 34.8 c 29.9 b 13.6 b 25.3 b 20.0 c 18.6 c 4.37 a 0.22 a 10.9 d Valencia 15.2 a 8.9 d 15.0 a 22.5 e 40.8 b 30.1 b 15.9 a 20.7 c 25.9 b 21.7 b 3.83 a 0.21 a 12.3 c CV (%) 10.9 14.7 15.4 8.9 9.9 5.8 8.7 10.7 17.4 4.3 13.5 8.6 7.8 F 51.3 50.4 3.32 24.8 44.2 99.7 23.7 32.3 15.6 135.0 2.99 14.9 40.5 p­value <0.0001 <0.0001 0.027 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 0.038 <0.0001 <0.0001 Orange varieties Mean FW (g·fruit­1) Fruit diameter (mm) Fruit height (mm) Rind thickness (mm) Juice content (g·kg­1) TTA (g·100 mL­1) TSS (°Brix) Vitamin C (g·100 g­1) Ratio TSS/TTA Kona 190 76.3 71.0 a z 3.81 b 545 0.798 b 11.5 a 60.0 a 14.5 c Lima 193 70.0 60.8 b 3.34 c 544 0.128 d 11.3 a 58.3 a 88.0 b Lima Verde 190 74.6 72.7 a 2.60 d 579 0.097 d 8.9 b 40.6 d 93.2 a Natal CNPMF­112 180 72.9 69.8 a 3.59 b 572 1.208 a 12.3 a 52.3 b 10.4 c Pera CNPMF D­6 205 74.9 75.6 a 3.12 c 548 0.670 c 8.9 b 43.5 d 14.7 c Rubi 187 75.9 70.0 a 4.15 a 539 0.617 c 11.3 a 49.2 c 18.7 c Sukkari 189 72.9 67.0 a 3.08 c 544 0.114 d 10.5 a 54.1 b 93.7 a Valencia Montemorelos 188 72.1 69.6 a 2.99 c 549 1.180 a 11.0 a 53.4 b 9.6 c CV (%) 8.2 3.5 5.9 6.0 4.2 11.0 7.2 7.1 8.2 F 0.63 2.01 3.38 18.62 1.15 142.1 7.56 10.00 397.2 p­value 0.723 0.126 0.025 <0.0001 0.385 <0.0001 0.0007 0.0002 <0.0001 Teodoro et al. ‐ Superior sweet oranges 145 min C contents, whereas ‘Lima Verde’ and ‘Pera’ had the lowest values. ‘Sukkari’ and ‘Lima Verde’ fol­ lowed by ‘Lima’ had the highest values of ratio, a proxy for fruit maturity (Table 2). FW, FD, and JC were not affected by scions (Table 2). Multivariate analyses Multivariate analysis helped to identify scion groups that performed homogeneously, considering the universe of all significant attributes. The first two PCA principal components explained more than 66% of the total observed variability, and the square cosine of the variables showed that, while average yield, CV, TTA, Prec., RT, TSS, and ratio were mostly associated with PC1, FH, alternate bearing, and vita­ min C contributed to most of the variation along PC2 (Fig. 2 a). Multi­correlation analysis indicated that average yield correlated positively with CV and that Prec. exhibited a positive correlation with total acidity, but both correlated negatively with ratio. In addition, while alternate bearing correlated positively with vit­ amin C, it had a negative correlation with FH (Fig. 2 a). Agglomerative hierarchical clustering analysis (AHC) using Shannon entropy for grouping all obser­ vations that showed similar results for the entire set of variables identified three distinct clusters (Fig. 2 c) with the following characteristics, as observed through the visual inspection of the observation cloud projection in the plane of the first two principal components of the PCA (Fig. 2 b). The heatmap of the results for all variables is shown in figure 2 c. The first cluster grouped all observations of ‘Kona’ and its main characteristics were high and alternate yields associated with bulk canopy and high vitamin C content; intermediate values for TSS, RT, Prec., acidi­ ty, FH, and low ratio. The second cluster included the observations of ‘Valencia Montemorelos’, ‘Rubi’, ‘Pera’ and ‘Natal CNPMF­112’. In general, these varieties showed intermediate values for all evaluated variables except ratio, which were mostly low for this cluster. Finally, the third cluster encompassed all observa­ tions of ‘Sukkari’, ‘Lima Verde’, and ‘Lima’. In contrast to the first and second clusters, the main characteris­ tic was that the ratio was high for all observations and average yield, CV, RT, and acidity were predomi­ nantly low. Intermediate values were observed for alternate bearing, vitamin C, TSS, and FH. 4. Discussion and Conclusions Here, we comparatively assessed vegetative, pro­ ductive, and fruit quality traits among eight sweet orange scions grafted on ‘Rangpur’ lime for enhan­ cing orchard varietal diversification under the tropi­ Fig. 2 ­ Principal Component and Agglomerative Hierarchical Clustering Analysis. (a) Correlation Circle of the variables; (b) Score plot of the observations in the plane of the two first Principal Components and (c) Heatmap of the rela­ tive values of all observations for all variables and group separation by the Agglomerative Hierarchical Clustering analysis (AHC). The first two axes (PC1 and PC2) account­ ed for 66.82% of the total variance. Arrows in green rep­ resent variables associated with PC1 whereas those in blue are associated with PC2 in figure a. Observations belonging to different groups by the AHC analysis were delineated (boxes) in figure b. CV: Canopy volume; AY: Average yield; ABI: Alternate Bearing Index; Vit.C: Vitamin C content; TSS: Total soluble solids content; RT: Rind thickness; Prec.: Precocity; TTA: Total titratable acid­ ity; FH: Fruit height. 146 Adv. Hort. Sci., 2023 37(2): 141­148 cal rainfed conditions of northeastern Brazil. Overall, the varieties reached peak yields in the fifth harvest, and subsequently decreased. The same pattern was observed for ‘Sincora,’ ‘Valencia Tuxpan,’ and ‘Pineapple’ sweet oranges in the same study region (Carvalho et al., 2019 a; Martins et al., 2020). As the experimental orchard was cultivated under rainfed conditions, predominantly negative yearly water bal­ ances possibly interfered with the productive poten­ tial of the different varieties. Major drought spells occurred in 2012, 2016, and 2018, with water deficits exceeding 480 mm. Water stress strongly impairs growth and development of citrus trees and sweet orange varieties commonly present water deficiency symptoms throughout the study region even when scions are grafted on drought­tolerant ‘Rangpur’ lime, which emphasizes the severe seasonal drought rainfed orchards face (Soares et al., 2015; Carvalho et al., 2016). As we did not specifically evaluate drought tolerance, further studies are needed to shed light on the susceptibility of sweet orange varieties to drought. Comparatively, ‘Kona’ was the most productive variety, with an annual average of 29.2 t·ha­1 of fruit. ‘Valencia Montemorelos’ (21.7 t.ha­1) and ‘Rubi’ (21.2 t·ha­1) also had remarkable yield performances. The high fruit yield of ‘Valencia Tuxpan’ grafted on ‘Santa Cruz Rangpur’ lime was also verified by Carvalho et al. (2019 a). Similarly, ‘CNPMF 003 Rangpur’ lime and ‘Santa Cruz Rangpur’ lime rootstocks conferred high yields to ‘Valencia’ in Brazil’s southeastern state of São Paulo (Fadel et al., 2018). The dominantly grown ‘Pera’, however, was characterized by intermediate yields. ‘Kona’ trees produced 72.5 t·ha­1 at its peak, and alongside ‘Rubi’ excelled in precocity, with yields that surpassed 23 t·ha­1 in the second harvest. Apart from ‘Lima Verde’ with lower values, all varieties had similar yield efficiencies despite the sharp differences in canopy volumesCVs. For instance, ‘Kona’ trees had the largest canopies (26.3 m3) in contrast with ‘Lima’ (11.4 m3) and ‘Pera’ (15.5 m3). This is consistent with similar yield efficiencies of ‘Pineapple’ sweet orange irrespective of the grafted rootstock in the same study region (Martins et al., 2020). It is noteworthy that after the two driest years (2012 and 2016), the most productive varieties were ‘Pera’ and ‘Valencia Montemorelos’. Melgar et al. (2010) showed that ‘Valencia’ sweet orange trees [grafted on ‘Swingle’ citrumelo C. paradisi Macfad. x Poncirus trifoliata (L.) Raf.] that experienced drought for a hundred days and were well irrigated in subsequent months pro­ duced more fruit than those that were not subjected to water stress. Alternate bearing is a widespread phenomenon among fruit trees in which high yield in one harvest is followed by low production in the subsequent har­ vest (Monselise and Goldschmidt, 1982). Alternate bearing is an undesirable trait from an economic standpoint, especially for mandarins and tangerines, but generally a minor to moderate problem for sweet oranges such as ‘Valencia’ (Monselise and Goldschmidt, 1982; Abobatta, 2019). Alternate bear­ ing in citrus is caused by fruit load inhibiting return flowering (Abobatta, 2019) and seemed here to be variety­specific, as ‘Kona’ possessed high propensity for yield alternation in contrast with less­prone ‘Lima Verde’, ‘Natal CNPMF­112’, ‘Pera’, ‘Sukkari’ and ‘Valencia Montemorelos’. ‘Lima’ and ‘Rubi’, in turn, had an intermediate degree of susceptibility to yield alternation. Nutrition, hormones, and abiotic stresses ranging from soil fertility and physical restrictions to drought susceptibility might also have played a role in yield fluctuation (Monselise and Goldschmidt, 1982; Abobatta, 2019; Carvalho et al., 2019 a, 2020). Fruit quality is expressed by several parameters including the amount of juice, TSS content, acidity level, and the amount of vitamin C (França et al., 2016; Lado et al., 2018; Tirado­Corbalá et al., 2020). Moreover, the TSS content is the basis for the pay­ ment of a premium price differential for high­quality fruit (Zhang and Ritenour, 2016). The ratio, or maturi­ ty index, expresses fruit ripeness and is also an indi­ cator of flavor (Lado et al., 2018; Ribeiro et al., 2020). These fruit quality traits may be influenced by the scion variety, management practices, maturity level, climate, and rootstocks (Al­Mohuei and Choumane, 2014; Carvalho et al., 2020; Ribeiro et al., 2020; Tirado­Corbalá et al., 2020). Here, we showed that FW, FD, and juice yield did not differ among the sweet orange varieties. However, ‘Lima’ trees pro­ duced smaller fruit than the other varieties. ‘Rubi’ produced the thickest and ‘Lima Verde’ the thinnest fruit rinds. ‘Lima Verde’ and ‘Pera’ produced the least sweet fruit, while ‘Natal CNPMF­112’ and ‘Valencia Montemorelos’ were the most acidic. The high fruit acidity of ‘Valencia’ grafted on ‘Santa Cruz Rangpur’ lime was also demonstrated by Rodrigues et al. (2019). There is evidence that rainfed orchards generally produce sweeter fruit, as lower juice yields related to water deficits favor sugar concentration (Lado et al., 2018). This is in line with higher fruit sugar contents Teodoro et al. ‐ Superior sweet oranges 147 of ‘Valencia’ trees subjected to deficit irrigation treat­ ments in Italy (Mossad et al., 2020). The ratio, or maturity index, was highest for ‘Lima Verde’ and ‘Sukkari’, which can be related to their lower acidity levels. ‘Kona’ and ‘Lima’ fruit had the highest con­ tents of vitamin C as opposed to the lowest values for ‘Lima Verde’ and ‘Pera’. Generally, the juice yields, TSS, and ratio values obtained here were with­ in the minimal requirements for Brazilian fresh orange markets. Multivariate analyses showed that fruit quality traits were mostly associated with PC1 (RT, TTA, TSS and ratio) while FH and Vit. C were strongly related to PC2. Ratio was negatively related to RT and espe­ cially to TTA. TSS, in turn, was associated with the majority of fruit quality traits, being negatively rela­ ted to FH (smaller fruit, higher TSS) and positively with RT, TTA and Vit. C. However, TSS was not related to ratio. PC2, which accounted for 25% of variability, was negatively related with FH and Vit. C contents, suggesting that smaller fruit concentrate more Vit. C. Collectively, our results obtained in northeastern Brazil highlight ‘Kona’, Valencia Montemorelos’ and ‘Rubi’ as superior sweet orange varieties for diversifi­ cation of tropical rainfed orchards. ‘Kona’ excelled in productive performance combined with a volumi­ nous canopy, precocity, sweet fruit with moderate acidity, and high levels of vitamin C despite the propensity for alternate yields and low ratio. ‘Valencia Montemorelos’ and ‘Rubi’ had high yield performances coupled with intermediate canopies, sweet fruit, moderate acidity (‘Rubi’) and vitamin C levels, low proneness for yield fluctuation (‘Valencia Montemorelos’), and high precocity (‘Rubi’), despite a low ratio. Acknowledgements We thank the Brazilian Agricultural Research Corporation (Embrapa) for financial support (project 20.18.01.007.00.00). References ABOBATTA W.F., 2019 ­ Management of alternative bea‐ ring in citrus varieties ‐ review. ‐ Adv. Agri. Tech. Plant Sci., 2(2): 180028. 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