Plant growth, yield and fruit quality of ‘Piemonte’ tangor grafted onto 14 rootstocks on the northern coast of the state of Bahia, Brazil

1Agronomist, Master of Science in Agrarian Sciences, Federal University of Recôncavo da Bahia, Cruz das Almas-BA. E-mails: natianafranca@ yahoo.com.br, m.s.amorim@hotmail.com. Master’s work of the first author with CAPES scholarship. 2Agronomist, researcher at Embrapa Cassava & Fruits, Cruz das Almas-BA. Emails: eduardo.girardi@embrapa.br, abelmon.gesteira@embrapa. br, orlando.passos@embrapa.br, walter.soares@embrapa.br Abstract In the state of Bahia, Brazil, citrus production is mainly on the Northern Coast region, with major cultivation of ‘Pera’ sweet orange grafted onto ‘Rangpur’ lime. The production of mandarins and mandarin-like fruits is very low in spite of the increasing regional consumption. Varieties that are adapted to tropical sub humid conditions should be evaluated on different rootstocks for cultivation recommendation. This study assessed the performance of ‘Piemonte’ tangor over 14 rootstocks in Rio Real, BA. Planting was performed in 2006 on a cohesive yellow argisol, at 6.0 m x 4.0 m spacing and with no irrigation. Plant growth, production, and physicochemical attributes of fruits in 2010-2014 were assessed, in addition to tree survival and drought tolerance based on leafroll. At nine years of age, rootstocks that induced greater cumulative production of ‘Piemonte’ were ‘Riverside’ and ‘Indio’ citrandarins, ‘Santa Cruz Rangpur’ lime, and ‘Cleopatra’, ‘Sunki Tropical’ and ‘Sunki Maravilha’ mandarins. Although four hybrid rootstocks were semidwarfing, their mean efficiency was equivalent to the other rootstocks (≈ 5.5 kg m-3), resulting in the lowest production. Drought tolerance and tree survival were similar among rootstocks with minimal loss, except for TSKFL x CTSW 049 hybrid with only 33.33% of survival. ‘Piemonte’ tangor produced fruits with general good quality under the evaluated conditions, but only peel thickness and technological index (TI) were influenced by rootstocks, with the lowest TI averages recorded for fruits harvested from scions grafted onto TSKC x (LCR x TR) 001 and ‘Volkamer’ lemon.


Introduction
In 2015, mandarin production in Bahia was 12,1 tons in an area destined to harvest of 759 ha.São Paulo is the largest producer in Brazil, with 356,3 tons, followed by Minas Gerais, Paraná, Rio Grande do Sul, Rio de Janeiro, Espírito Santo, Goiás, Paraíba, and Bahia, the ninth national producer (IBGE, 2015).Bahia's production is well below the state's demand, which is why there is the possibility of local production, since varieties adapted to the Coastal Tablelands conditions are known and high quality fruits can be produced in the region.
In northeastern Brazil, mandarins and their hybrids are primarily grafted onto 'Rangpur' lime (Citrus limonia Osbeck), and their fruits do not have good quality for marketing on a large scale, because mandarin fruits are frequently greenish, tasteless and subject to granulation, as generally noted for mandarins cultivated in tropical climate (REUTHER, 1973;JOMORI et al., 2014).Therefore, new varieties of mandarins and mandarin-like fruits, preferably more adapted to the tropical sub humid climate, and alternative rootstocks are demanded in the region.
'Piemonte' tangor is a 'Clementine' mandarin hybrid (C.clementina hort.ex Tanaka) with 'Murcott' tangor [unknown origin, probably a natural C. reticulata Blanco with sweet orange C. sinensis (L.) Osbeck hybrid], introduced from California, USA, with midseason to late fruit maturation, medium-sized fruits with globe to flat shape, similar to Murcott' tangor fruits, but with earlier maturation and more intense orange peel color in Northeastern Brazil (PASSOS et al., 2007;ALMEIDA;PASSOS, 2011).These characteristics, combined with resistance to transportation and high productivity, make this cultivar a real option to the citrus diversification in the region (MARTINS et al., 2015).
Rootstocks alternative to 'Rangpur' lime must present high drought tolerance and perform well in dry farming, condition prevalent in the citrus belt of northeastern Coastal Tablelands.This area is characterized by soils with low water retention and high subsurface density associated with periods of drought in the summer; these conditions result in severe water deficiency to plants that decreases yield (CINTRA, 2007).Good grafting compatibility is also a requirement, considering that 'Murcott' tangor is incompatible with trifoliate orange [Poncirus trifoliata (L.) Raf.] and some of its hybrids (POMPEU JUNIOR, 2005).In addition, information about the performance of 'Piemonte' tangor grafted onto different rootstocks is scarce (CARVALHO et al., 2016;MARTINS et al., 2015MARTINS et al., , 2016)).
In this study, plant growth, yield and fruit quality of 'Piemonte' tangor were assessed on 14 rootstocks in dry farming on the northern coast of the state of Bahia.

Material and Methods
The experiment was installed on June 2006 at 6.0 m x 4.0 m in the municipality of Rio Real, northern coast of the state of Bahia (11°29'07" S, 37°56'04" W, 179 m above sea level) and cultivation was dry farming.Climate, meteorological variables, soil, and cultural practices are exactly the same reported by França et al. (2016) evaluating a similar trial with 'Tuxpan Valencia' sweet orange in the same period and next to the experimental area.
'Piemonte' tangor was assessed on the following rootstocks: 'Sunki' [C. sunki (Hayata)  Plant growth assessments were annually performed from 2010 to 2014, by measuring height (H) and mean diameter (D) of canopy (mean of diameters in the row direction, and in the perpendicular row direction), and canopy volume (V) (m³) estimated by V = 2/3 x π x D 2 /4 x H (SILVA et al., 2013).Production per tree was measured from 2010 to 2014.The average production efficiency in the period from 2010 to 2014 was also calculated by the average ratio between annual productions and canopy volumes in the respective years.Tree size results were presented only for 2014, at nine years of age.
Water deficiency tolerance was estimated during a severe drought period, which occurred on March 2013, using a scale of scores based on visual leafroll symptoms ranging from score 1 (absence of symptoms), score 2 (discreet withering up to half of the canopy), score 3 (discreet withering on whole canopy) and score 4 (intense withering along the entire canopy and with falling leaves), performed by four evaluators (Figure 1).Survival was calculated by the percentage of living trees until 2014.
The experimental design was randomized blocks, with 14 treatments, three replicates and two plants in the plot.Results were submitted to analysis of variance and averages grouped by the Scott-Knott test (P ≤ 0.05), transforming data by (x + 0.5) ^ 0.5 whenever necessary in order to meet the normality and homogeneity of variance.Data on water deficiency tolerance were analyzed by the non-parametric test of Kruskal-Wallis (P ≤ 0.05).

Results and discussion
The assessed rootstocks resulted in differences in canopy size of 'Piemonte' tangor in 2014 (Table 1).Rootstocks were grouped into two categories according to the canopy size: diameter and volume.The highest diameters were obtained with 'Cleopatra', 'Sunki Maravilha' and 'Sunki Tropical' mandarins, 'Santa Cruz Rangpur' lime, 'Volkamer' lemon, 'Riverside' and 'Indio' citrandarins, and TSKC x CTSW -028, TSKC x (LCR x TR) -018 and TSKC x (LCR x TR) -001 (from 2.6 to 3.1 m) hybrids, and the smaller diameters were found in CLEO x CTCZ -226, TSKFL x CTTR -017, TSKFL x CTSW -049 and LVK x LVA -009 (from 1.5 to 2.2 m).The largest and the smallest canopy volumes followed the same groups, from 8.7 to 13.9 m 3 and from 2.7 to 6.0 m 3 , respectively.On the other hand, plant height and production efficiency were similar among evaluated rootstocks, on average 2.3 m and 5.5 kg m -3 , respectively (Table 1).Rootstock  N. de O. França et al.
TSKFL x CTSW -049 hybrid rootstocks led to only 33.33% of tree survival nine years after planting, while loss of trees was minimal among the other rootstocks (Table 1).Similar results were reported for 'Tuxpan Valencia' sweet orange (FRANÇA et al., 2016), highlighting issues possibly related to graft incompatibility and poor plant growth with this hybrid in particularly.No blight symptoms were observed at nine years of age.It is also noteworthy that 'Piemonte' tangor had alternaria brown spot symptoms that resembled those of 'Murcott' tangor (PACHECO et al., 2012), even though its susceptibility was not investigated in this experiment.Drought tolerance was evaluated on March 2013 (accumulated deficit > 300 mm), but rootstocks did not differ based on a visual leafroll scale (Table 1: Figure 1).
In the cumulative production assessment for 'Piemonte' tangor during the period from 2010 to 2014 (five initial harvests), it was observed that 'Riverside' and 'Indio' citrandarins, 'Santa Cruz Rangpur' lime, and 'Cleopatra', 'Sunki Tropical' and 'Sunki Maravilha' mandarin rootstocks induced 190.6 to 108.7 kg tree -1 , outperforming the other groups, resulting in less than 95.7 kg tree -1 (Table 2).The rootstocks that have maintained good production in relation to the others, always being annually in the most productive groups, were 'Riverside' citrandarin and 'Sunki Tropical' mandarin, whereas 'Cleopatra' and 'Sunki Maravilha' mandarins induced later productions.Yield variations were observed throughout the years for all rootstocks, with expressive reductions in 2012 and 2013 as a result of the prolonged drought from late 2011 to 2013 (FRANÇA et al., 2016).Plant growth, yield and fruit quality of 'Piemonte' tangor grafted... Harvest was conducted in different periods in each season, due to the alternating periods of drought and rain on the location (FRANÇA et al., 2016).In the year 2010, there was only one production in the month of July; in 2011, the highest production was in October, with another harvest in July; in 2012, there were four harvests, in January, June, August and November, being the major harvest in November; in 2013, there was only one harvest in March; finally, in 2014, there were two productions, one in January and other in June, with the largest production in January.Despite the irregular behavior regarding harvesting, an average cycle of ≈ 9 months from blossom to harvest of 'Piemonte' tangor could be observed on the northern coast of Bahia.
Regarding fruit quality, rootstocks have not altered most of the assessed attributes (Table 3).Only peel thickness and technological index (TI) were influenced by rootstocks.'Cleopatra', 'Sunki Tropical' and 'Sunki Maravilha' mandarins, 'Riverside' citrandarin and the hybrid TSKC x CTSW -028 led to thinner fruit peel of 'Piemonte' tangor.The lowest TI averages were recorded for fruits of trees grafted onto TSKC x (LCR x TR) -001 and 'Volkamer' lemon.
The differences in plant size observed for 'Piemonte' tangor on the evaluated rootstocks do not allow for high density orchards, since the four semi-dwarfing rootstocks (CLEO x CTCZ -226, TSKFL x CTTR -017, TSKFL x CTSW -049 and LVK x LVA -009) did not compensate the lower production per tree with higher efficiency per canopy volume (Table 1).Although there was no difference regarding mean production efficiency, the evaluated rootstocks varied from 3.3 to 8.6 kg m -3 with the most vigorous varieties such as 'Riverside' citrandarin resulting in higher production per tree.Carvalho et al. (2016), evaluating 'Piemonte' tangor grafted onto 11 rootstocks on the Coastal Tablelands of Sergipe, Brazil, observed smaller trees and higher production efficiency on 'Swingle' citrumelo and on HTR -051 trifoliate hybrid.The truly dwarfing rootstocks of 'Flying Dragon' trifoliate orange (P.trifoliata) and 'Troyer' and 'Carrizo' tetraploid citranges yielded from 8.9 to 12.1 kg m -3 of 'Span American' mandarin (C.reticulata) associated with 70% to 50% reduction in the canopy volume (SILVA et al., 2013).
'Sunki Maravilha' mandarin performed well as rootstock for 'Piemonte' tangor (Tables 1 to 3), but showed poor performance when grafted onto 'Tuxpan Valencia' sweet orange (FRANÇA et al., 2016).Therefore, its use should be further investigated as it is sensitive to drought and this may limit yield (SANTANA-VIEIRA et al., 2016).On the other hand, TSKC x CTSW -028 induced higher production to 'Valencia' sweet orange in rain-fed cultivation in São Paulo, Brazil (RAMOS et al., 2015), which in turn was also not observed for 'Tuxpan Valencia' in Bahia (FRANÇA et al., 2016).TSKC x (LCR x TR) -018 was also promising for 'Piemonte' tangor, as a result of intermediate production, and other hybrids from the same cross were also highlighted in previous work (RAMOS et al., 2015).
Fruit quality of 'Piemonte' tangor was not remarkably influenced by rootstocks, which corroborates previous works with this variety and other mandarin hybrids in Brazil (FIGUEIREDO et al., 2006;MOURÃO FILHO et al., 2007;ESPINOZA-NUÑEZ et al., 2007, 2008;LEDO et al., 2008;STUCHI et al., 2008;CARVALHO et al., 2016;MARTINS et al., 2015MARTINS et al., , 2016)).In this work, mean fruit traits were: 220 g of weight; 6.42 cm x 7.70 cm of fruit size (length x width, given a relation of 0.83, which indicates flat fruits similar to those of 'Murcott' tangor); peel thickness of 2.0 mm; 48% of juice content with 16 seeds per fruit; 0.63% of titratable acidity and 11.61 o Brix, resulting in maturity index (SS/TA) of 20; and 2.28 kg of SS per 40.8 kg box.Despite the large fruits with high number of seeds, 'Piemonte' tangor met the Brazilian standards for mandarin commercialization in the domestic market (CEAGESP, 2011).
Regarding the average fruit production, assessed on the most productive rootstock in 2010-2014 (Table 2), at 6.0 m x 4.0 m tree spacing, 'Piemonte' tangor yielded 15.9 t ha -1 , which is similar to the state of Bahia (15.9 t ha -1 ), but significantly lower than the state of São Paulo (31.4 t ha -1 ) and the mean Brazilian mandarin productivity in 2015 (19.4 t ha -1 ), respectively (IBGE, 2015).On the other hand, the same mean yield increased to 38.6 t ha -1 in 2014, that is, taken the fifth harvest alone (Table 2).Great differences in climate, soil and cultural practices among production regions should be considered for this comparison.

2
Average from 2010-2014. 3Visual score scale for drought symptoms ranging from score 1 (absence of symptoms), score 2 (discreet withering up to half of the canopy), score 3 (discreet withering in whole canopy) and score 4 (intense withering along the entire canopy and with falling leaves), evaluated at eight years old (March 2013).Averages followed by the same letter in column are equivalent by the non-parametric test of Kruskal-Wallis (P ≤ 0.05).

Figure 1 .
Figure 1.Visual score scale for drought symptoms ranging from score 1 (absence of symptoms) (A), score 2 (discreet withering up to half of the canopy) (B), score 3 (discreet withering in whole canopy) (C), and score 4 (intense withering along the entire canopy and with falling leaves) (D) of 'Piemonte' tangor [Citrus clementina hort.ex Tanaka x 'Murcott' tangor (C.reticulata Blanco x C. sinensis (L.) Osbeck)] grafted onto 14 rootstocks in rainfed cultivation in Rio Real-BA at eight years old.
Averages followed by the same letter in column belong to the same group by the Scott-Knott test (P ≤ 5%).