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1 This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier s archiving and manuscript policies are encouraged to visit:

2 Scientia Horticulturae 129 (2011) Contents lists available at ScienceDirect Scientia Horticulturae journal homepage: Performance of Tahiti lime on twelve rootstocks under irrigated and non-irrigated conditions Erick Espinoza-Núñez a, Francisco de Assis Alves Mourão Filho a,, Eduardo Sanches Stuchi b, Tatiana Cantuarias-Avilés a, Carlos Tadeu dos Santos Dias a a Universidade de São Paulo, Escola Superior de Agricultura Luiz de Queiroz, Piracicaba, SP, Brazil b Embrapa Mandioca e Fruticultura Tropical, Estação Experimental de Citricultura de Bebedouro, Bebedouro, SP, Brazil article info abstract Article history: Received 6 October 2010 Received in revised form 14 March 2011 Accepted 18 March 2011 Keywords: Citrus latifolia Dwarfing Flying Dragon High density planting Interstock Poncirus trifoliata Faced with new challenges, such as emerging diseases, shortening of orchard longevity, and larger social and environmental demands from consumers, practices such as rootstock diversification, irrigation and high density plantings have become relevant for the Brazilian citrus industry. This research had the objective to evaluate the performance of irrigated and non-irrigated Tahiti lime trees grafted on 12 rootstocks and one interstock. Plots were distributed following a randomized block design, with four replicates and one plant per plot. Rootstocks influenced plant vigor, especially Flying Dragon trifoliate, which reduced tree height by approximately 47% compared to the Rangpur lime. Trees that were budded on more vigorous rootstocks showed higher yield when grown without irrigation than with irrigation. The 1646 citradia and Morton citrange rootstocks performed particularly well. On the other hand, the plants on less vigorous rootstocks showed better performance in terms of yield under irrigation than the same combinations without irrigation, especially those grafted on the tetraploid Carrizo and Troyer citranges, Swingle citrumelo, Davis A trifoliate and Flying Dragon trifoliate. Plants budded on the 1708 citradia had high yields under irrigated and non-irrigated conditions. The effect of interstock on plant vigor was dependent of rootstock. Interstocked plants on Davis A trifoliate were higher than those without interstock. On the other hand, interstocked plants on Catania 2 Volkamer lemon were less vigorous than those without interstock Elsevier B.V. All rights reserved. 1. Introduction The citrus industry faces new challenges worldwide, including emergence of diseases, shortening of orchard life span, and larger social and environmental demands imposed by consumers. In Brazil, four varieties of sweet orange represent nearly 92% of the citrus plants in the State of São Paulo, and a single type of rootstock, the Rangpur lime, accounts for 85% of the rootstocks used in citrus groves (Bové and Ayres, 2007). In this context, rootstock diversification, irrigation and high density planting practices become relevant. On the other hand, production and international market of Tahiti lime have significantly expanded in the recent years. In order to sustain this developing market, it is very important to create adequate conditions to extent Tahiti lime harvest period, with rootstock diversification and irrigation. Over 85% of the citrus groves in Brazil are not irrigated. Experiments involving Tahiti Corresponding author. Tel.: ; fax: address: francisco.mourao@usp.br (F.A.A. Mourão Filho). lime are scarce, but the partial results already allow to characterize some rootstocks (Stuchi et al., 2003; Stenzel and Neves, 2004). Considering that there has been a growing interest in Tahiti lime production driven by the need for higher crop yields and the possibility of producing fruit during the off-season period, at higher market prices, the objective of this study was to evaluate the performance of irrigated and non-irrigated Tahiti lime trees budded on 12 rootstocks and on one interstock. 2. Materials and methods 2.1. Field trial and plant material Trees were planted in December of 2003 in the northern São Paulo State, Brazil ( S latitude; W longitude; 601 m altitude) on an 8.0 m 5.0 m tree spacing, corresponding to a plant density of 250 trees ha 1. The soil was Haplustox with a medium texture (38% clay), and the climate was Köeppen s Cwa, with maximum and minimum temperatures of 30.5 C and 16.8 C, respectively, and an annual rainfall of mm. IAC- 5 Tahiti lime (Citrus latifolia (Yu. Tanaka) Tanaka) was grafted /$ see front matter 2011 Elsevier B.V. All rights reserved. doi: /j.scienta

3 228 E. Espinoza-Núñez et al. / Scientia Horticulturae 129 (2011) on the following rootstocks (treatments): the trifoliates Flying Dragon (Poncirus trifoliata) and Davis A ; the tetraploid Troyer and Carrizo citranges and the Morton citrange [Citrus sinensis (L.) Osbeck P. trifoliata]; the citradias (Citrus aurantium P. trifoliata) 1646 and 1708 ; Swingle citrumelo (Citrus paradisi P. trifoliata); Catania 2 Volkamer lemon (Citrus volkameriana V. Ten. & Pasq.); Orlando tangelo (Citrus reticulata Blanco C. paradisi Macf.); Smooth Flat Seville (SFS) (C. aurantium L.) sour orange and the Rangpur lime (Citrus limonia Osbeck). Flying Dragon trifoliate was also used as interstock for Catania 2 Volkamer lemon, Orlando tangelo, Morton citrange, Swingle citrumelo, SFS sour orange, and Davis A trifoliate. Plants grafted on Orlando tangelo (not interstocked) and on SFS sour orange (interstocked) died in 2007 due to root rot caused by Phytophthora spp. The experiment was not pruned, and was managed according with regular cultural practices. The annual rate of fertilization was equivalent to 190 g N, 110 g P and 116 g K tree 1 as mono ammonium phosphate and The experimental orchard was surrounded by several other citrus evaluation experiments Plant yield and fruit quality measurements Plant height (H) and width (in parallel, D l, and perpendicular, D r, direction to the row) were measured, in 2009 to calculate the canopy volume according to the equation V =(/6) H D l D r (Zekri, 2000). Fruit harvests were recorded from 2007 to Under local conditions, Tahiti limes bloom throughout the entire year, leading to a total of three to five harvests evaluated each year. In 2009, yield efficiency was computed from the relationship between the fruit yield (kilograms per plant) and the canopy volume (cubic meters per plant). Yield was recorded on every commercial harvest, and cumulative yield was calculated for two periods, which include the following: from the second year through the fourth year after planting ( ) to estimate early-bearing cumulative yield and from the second year through the sixth year after planting ( ) to evaluate total cumulative yield Experimental design and statistical analysis The plots were distributed following a randomized block design, with 18 treatments, four replications and one plant per plot. The same experiment was conducted both with and without irrigation. In the irrigated experiment trees were drip irrigated based on a 100% of the crop evapotranspiration (ET c ). The system was comprised of a drip line in each tree row, with three self-compensating drippers (2.3 l h 1 ) per tree, which were 1.0 m apart. For each variable, row data were initially submitted to exploratory analysis to verify whether they meet the assumptions of homogeneity of variances, normality of errors, and presence of outliers. Data were submitted to analysis of variance, using Fisher s test. Original data of some variables were transformed using the Box Cox method (Montgomery, 2005). For each variable, the individual and joint analyses of variances were performed. Comparisons among means were performed by the Scott Knott test (P < 0.05), while the effect of interstock was tested by contrasts. 3. Results 3.1. Plant height and canopy volume The rootstock clearly affected plant growth. In the non-irrigated experiment, the more vigorous plants reached approximately 3.6 m in height and had 33 m 3 of canopy volume, while in the irrigated experiment, the more vigorous plants were 4.0 m in height and had 45 m 3 of canopy volume six years after planting. In both experiments, the rootstock that produced the most vigorous Tahiti lime plants were Catania 2 Volkamer lemon, Orlando tangelo, Morton citrange and Swingle citrumelo (Table 1). In the non-irrigated trial, plants with intermediate vigor were approximately 3.2 m in height, with 26 m 3 of canopy volume, while in the irrigated trial, plants were 3.7 m in height and had 36 m 3 of canopy volume. In both experiments, the rootstocks Rangpur lime, the 1646 and 1708 citradias, the tetraploid Carrizo and Troyer citranges and the Davis A trifoliate induced intermediate vigor to the Tahiti lime scion. In both experiments, Flying Dragon trifoliate and SFS sour orange rootstocks induced plant dwarfing (Table 1). Low vigor (or dwarf) plants had their canopy volume reduced by one-third to one-half compared to Rangpur limes. Irrigation promoted vegetative plant growth on all the rootstocks; plant height was increased by 11% and the canopy volume by approximately 36%. The interstock had no effect on plant height and canopy volume in both experiments. Some contradictory and unexpected effects of interstock were observed, such as increasing plant vigor on Davis A trifoliate and decreasing plant vigor on Catania 2 Volkamer lemon (Table 1) Yield In the fourth year after planting, fruit yield in the irrigated experiment was 149% larger than in the non-irrigated experiment, demonstrating the influence of irrigation on early yield (Table 2). In the fifth and sixth years after planting, higher yields were observed in plants on Catania 2 Volkamer lemon, 1646 citradia, 1708 citradia, Orlando tangelo, Morton citrange and Swingle citrumelo (Table 2). Rootstocks influenced the early-bearing cumulative yield (second year through fourth year after planting) (Table 3). In the non-irrigated experiment, the rootstocks Catania 2 Volkamer lemon, 1646 and 1708 citradias, Orlando tangelo and Morton citrange induced a larger percentage of early-bearing yields. In the irrigated experiment, larger early-bearing was observed on the 1646 and 1708 citradias as well as on the Morton citrange (Table 3). Furthermore, trees on Volkamer lemon and Orlando tangelo acted similarly in both experiments. These results indicated that irrigation induced higher fruit yields in most rootstocks, including a 257% increase in the Rangpur lime, a 379% increase in the Carrizo citrange tetraploid, a 324% increase in the Troyer citrange tetraploid, and a 432% increase in the Davis A trifoliate (Table 3). Rootstocks also influenced the cumulative yield, from the second year through the sixth year after planting (Table 3). In both experiments, larger cumulative yields were observed for plants on Catania 2 Volkamer lemon, the 1646 and 1708 citradias, Orlando tangelo and Morton citrange (Table 3). The interstock induced higher fruit production in plants on Davis A trifoliate in both experiments. The irrigated plants produced an average of 42% more fruits than non-irrigated ones. Paradoxically, 1646 citradia, Orlando tangelo, SFS sour orange and Flying Dragon trifoliate rootstocks produced similarly in both experiments. However, plants grafted on tetraploid Carrizo and Troyer citranges, Swingle citrumelo and Davis A trifoliate increased their cumulative production by more than 60% when irrigated (Table 3). Yield efficiency after six years from planting was affected by the rootstocks (Table 3). In the non-irrigated experiment, the plants on Flying Dragon trifoliate showed high yield efficiency due to its small canopy. In this condition, the competition between fruit for water, carbohydrates and minerals is more intense than in plants with lower yield efficiency. In the irrigated experiment, higher yield efficiency was observed in plants on 1646 and 1708 citradias, tetraploid Troyer citrange, Swingle citrumelo, Davis A trifoliate

4 E. Espinoza-Núñez et al. / Scientia Horticulturae 129 (2011) Table 1 Plant height and canopy volume of Tahiti lime on different rootstocks, interstocked or not interstocked, under irrigated and non-irrigated conditions. Brazil, Rootstocks Interstock Non-irrigated experiment Irrigated experiment Plant height (m) Canopy volume (m 3 ) Plant height (m) Canopy volume (m 3 ) Rangpur lime 3.33 ± 0.10b ± 1.1b 3.65 ± 0.02b ± 1.4b Catania 2 Volkamer lemon 3.65 ± 0.08a ± 0.9a 4.10 ± 0.05a ± 1.0a Catania 2 Volkamer lemon Flying Dragon 3.23 ± 0.09b ± 1.3b 3.97 ± 0.10a ± 1.3a 1646 citradia 3.35 ± 0.21b ± 2.8a 3.70 ± 0.23b ± 4.3b 1708 citradia 3.18 ± 0.08b ± 1.5b 3.77 ± 0.06b ± 1.3b Orlando tangelo Flying Dragon 3.75 ± 0.06a ± 0.5a 4.02 ± 0.15a ± 2.2a Morton citrange 3.61 ± 0.18a ± 5.0a 4.17 ± 0.03a ± 1.0a Morton citrange Flying Dragon 3.73 ± 0.12a ± 1.9a 4.23 ± 0.13a ± 2.1a Carrizo citrange tetraploid 3.46 ± 0.06a ± 2.1b 3.78 ± 0.09b ± 2.6b Troyer citrange tetraploid 3.45 ± 0.02a ± 2.6b 3.89 ± 0.21a ± 3.5b Swingle citrumelo 3.54 ± 0.15a ± 3.2a 3.93 ± 0.03a ± 3.2b Swingle citrumelo Flying Dragon 3.62 ± 0.12a ± 1.3b 3.90 ± 0.00a ± 2.4b Davis A trifoliate 3.08 ± 0.20b ± 3.4b 3.39 ± 0.11c ± 4.3b Davis A trifoliate Flying Dragon 3.44 ± 0.09a ± 1.5b 3.64 ± 0.09b ± 3.4b Flying Dragon trifoliate 2.33 ± 0.12c 8.06 ± 1.2d 2.44 ± 0.07d ± 0.8d SFS sour orange 2.59 ± 0.10c ± 1.1c 3.20 ± 0.18c ± 3.1c Mean CV (%) Contrast Non-interstocked plants 3.47a 31.30a 3.90a 42.88a Interstocked plants 3.50a 31.60a 3.93a 42.33a Interaction Rootstocks Irrigation in plant height (P = ) and canopy volume (P = ). Means followed by different letters in columns are significantly different (P < 0.05) by Scott Knott s test. Values represent means ± SE. and Flying Dragon trifoliate. In general, non-irrigated plants on less invigorating rootstocks showed higher yield efficiency than the plants watered and grafted on more invigorating rootstocks (Table 3). 4. Discussion The low vigor and high yield efficiency traits of plants budded on Flying Dragon trifoliate suggest that this rootstock is suitable for high density plantations (Stuchi et al., 2003; Cantuarias- Avilés et al., 2010). Plants on Flying Dragon trifoliate occupied an area of 5.78 m 2.79 m in the irrigated experiment and an area of 5.05 m 2.17 m in the non-irrigated trial, as calculated from plant diameter measured after 6 years from planting, assuming 15% of tree overlapping along the row (De Negri et al., 2005). These plant spacings, however, corresponded to six-year-old plants. Therefore, lower plant density would be expected when the plants reach their final size. Researchers have recommended planting spacings of m between the rows, and m between plants along the row for Tahiti limes on Flying Dragon trifoliate (Stuchi and Silva, 2005). In this recommendation, however, the overlapping between canopies seems to exceed 15%. Another important feature of Flying Dragon trifoliate rootstock is its high resistance to root rot caused by Phytophthora spp., observed even in irrigated orchards (Stuchi and Silva, 2005). Nonetheless, Flying Dragon trifoliate seems inappropriate as a rootstock for Hamlin Table 2 Fruit yields in the fourth, fifth and sixth years after planting of Tahiti lime on different rootstocks, interstocked or not interstocked, under irrigated and non-irrigated conditions. Brazil, Rootstocks Interstock Non-irrigated experiment Irrigated experiment Fourth Fifth Sixth Fourth Fifth Sixth Rangpur lime 16.9 ± 3.2b 47.8 ± 2.6a ± 13.3c 48.9 ± 3.0b * 58.9 ± 4.7b ± 6.9b Catania 2 Volkamer lemon 37.4 ± 8.2a 68.7 ± 8.5a ± 14.3b 60.6 ± 5.5a * 88.9 ± 5.4a ± 5.3a Catania 2 Volkamer lemon Flying Dragon 34.9 ± 10.3a 78.8 ± 5.9a ± 11.6b 40.7 ± 1.7b ± 10.5a ± 17.3b 1646 citradia 31.2 ± 3.3a 60.7 ± 9.9a ± 5.1b 60.8 ± 8.9a * 67.3 ± 3.8b ± 11.6b 1708 citradia 33.6 ± 3.0a 60.9 ± 6.6a ± 10.2b 67.9 ± 3.5a * 69.7 ± 11.0b ± 10.7a Orlando tangelo Flying Dragon 38.2 ± 3.5a 61.6 ± 3.9a ± 4.6a 44.3 ± 16.1b 71.6 ± 15.3b ± 21.5a Morton citrange 18.4 ± 6.2b 59.2 ± 9.9a ± 12.5a 80.5 ± 5.9a * 83.1 ± 7.4a ± 15.6a Morton citrange Flying Dragon 21.5 ± 4.7b 61.3 ± 5.7a ± 7.9a 60.3 ± 5.9a * 64.9 ± 3.1b ± 9.5a Carrizo citrange tetraploid 5.1 ± 1.0c 24.3 ± 1.4b 73.9 ± 14.3d 44.8 ± 0.9b * 41.9 ± 0.3c ± 5.3b Troyer citrange tetraploid 14.1 ± 4.8b 41.4 ± 6.2b 85.8 ± 9.2c 40.4 ± 1.3b * 63.8 ± 5.3b ± 21.9b Swingle citrumelo 22.5 ± 6.7b 35.6 ± 10.9b ± 17.3b 58.1 ± 3.5a * 82.4 ± 11.9a ± 10.1b Swingle citrumelo Flying Dragon 16.5 ± 1.0b 49.2 ± 7.1a ± 25.8b 70.2 ± 6.4a * 51.6 ± 4.4c ± 15.7a Davis A trifoliate 4.1 ± 1.1c 33.5 ± 9.0b ± 20.2c 23.6 ± 2.0c * 37.9 ± 5.9c ± 23.2b Davis A trifoliate Flying Dragon 13.1 ± 2.9b 54.8 ± 8.2a ± 12.6b 50.5 ± 7.3c * 71.2 ± 10.3b ± 18.7a Flying Dragon trifoliate 2.7 ± 0.8c 14.8 ± 2.1c 67.3 ± 9.8d 18.5 ± 2.1c * 29.1 ± 5.7c 59.6 ± 2.7c SFS sour orange 0.13 ± 0.1c 6.4 ± 1.5c 51.5 ± 14.8d 3.7 ± 0.2d 19.5 ± 3.0c 54.1 ± 5.1c Mean CV (%) Contrast Non-interstocked plants b Interstocked plants a Interaction Rootstocks Irrigation in fourth (P < ), fifth (P = ) and sixth (P = ) years. Means followed by different letters in columns are significantly different (P < 0.05) by Scott Knott s test. Values represent means ± SE. * P < 0.05, rootstock differs between irrigated and non-irrigated experiments.

5 230 E. Espinoza-Núñez et al. / Scientia Horticulturae 129 (2011) Table 3 fruit yield (second to fourth years and second to sixth years after planting) and yield efficiency of Tahiti lime on different rootstocks, interstocked or not, under irrigated and non-irrigated conditions. Brazil, Rootstocks Interstock Non-irrigated experiment Irrigated experiment yield 2 4 years yield 2 6 years Yield efficiency a (kg m 3 ) yield 2 4 years yield 2 6 years Yield efficiency (kg m 3 ) Rangpur lime 17.3 ± 3.6b ± 11.1c 4.1 ± 0.51b 55.0 ± 1.4b * ± 9.7b 3.0 ± 0.27b Catania 2 Volkamer lemon 60.7 ± 9.7a ± 20.0a 3.9 ± 0.38b 72.1 ± 6.4b ± 10.0a 3.6 ± 0.04b Catania 2 Volkamer lemon Flying Dragon 50.6 ± 8.8a ± 19.6a 4.3 ± 0.43b 61.7 ± 2.5b ± 25.1a 3.3 ± 0.34b 1646 citradia 38.8 ± 2.8a ± 14.3a 4.6 ± 0.63b 77.3 ± 14.6a * ± 24.4a 4.3 ± 0.29a 1708 citradia 45.2 ± 2.7a ± 17.4a 4.6 ± 0.36b 76.7 ± 5.4a * ± 16.3a 5.2 ± 0.45a Orlando tangelo Flying Dragon 48.6 ± 5.5a ± 5.2a 3.9 ± 0.08b 56.4 ± 20.6b ± 56.0a 3.6 ± 0.39b Morton citrange 31.7 ± 5.2a ± 20.3a 4.9 ± 0.49b 96.8 ± 7.5a * ± 22.9a 4.2 ± 0.42a Morton citrange Flying Dragon 38.4 ± 6.6a ± 15.7a 4.2 ± 0.10b 87.4 ± 7.7a * ± 16.7a 3.3 ± 0.18b Carrizo citrange tetraploid 16.2 ± 4.5b ± 17.3d 2.8 ± 0.46b 58.0 ± 4.0b * ± 8.1b 3.5 ± 0.11b Troyer citrange tetraploid 19.8 ± 8.7b ± 23.4c 3.3 ± 0.38b 51.7 ± 5.5b * ± 28.1b 4.1 ± 0.63a Swingle citrumelo 32.7 ± 5.9a ± 33.8b 3.4 ± 0.22b 64.5 ± 1.9b * ± 18.7a 3.9 ± 0.14a Swingle citrumelo Flying Dragon 27.8 ± 5.1b ± 36.8b 4.5 ± 0.84b 88.3 ± 7.8a * ± 21.5a 4.8 ± 0.18a Davis A trifoliate 9.2 ± 2.9b ± 27.7c 4.1 ± 0.46b 34.7 ± 2.9c * ± 23.7b 4.6 ± 0.12a Davis A trifoliate Flying Dragon 22.7 ± 3.5b ± 23.2b 4.2 ± 0.43b 69.9 ± 11.1b * ± 36.6a 4.9 ± 0.53a Flying Dragon trifoliate 9.3 ± 0.7b 91.3 ± 9.7d 8.4 ± 0.40a 30.2 ± 1.3c * ± 4.6c 4.4 ± 0.31a * SFS sour Orange 0.1 ± 0.1b 58.1 ± 15.7d 3.6 ± 0.97b 6.2 ± 0.9d 79.8 ± 3.4c 2.5 ± 0.18b Mean CV (%) Contrast Non-interstocked plants Interstocked plants Interaction Rootstocks Irrigation in cumulative yield 2 4 years (P = ), cumulative yield 2 6 years (P = ) and yield efficiency (P = 0.003). Means followed by different letters in columns are significantly different (P < 0.05) by Scott Knott s test. Values represent means ± SE. a Yield efficiency was calculated from the relationship between fruit yield and canopy volume (m 3 ). * P < 0.05, rootstock differs between irrigated and non-irrigated experiments. and Valencia sweet oranges, Redblush grapefruit and Murcott tangor because the plants are too small and low yielding (Rabe, 1996; Wheaton et al., 1991). In Japan and the United States, Flying Dragon trifoliate is used as a rootstock for Satsuma mandarins in greenhouse crops (Nesbitt et al., 2008). The mechanism by which rootstocks, such as Flying Dragon trifoliate, induce growth reduction on grafted plants is still unknown (Solari and DeJong, 2006). The effect of Flying Dragon as an interstock on vegetative growth and fruit production was influenced by the rootstock. It was observed that on the Catania 2 Volkamer lemon rootstock, the interstock reduced plant size, while on the Davis A trifoliate, it increased plant size. The use of Flying Dragon trifoliate interstock also caused differences in vegetative growth on different rootstocks in Star Ruby grapefruit and Michal and Nova mandarins (Ashkenazi et al., 1992). On the other hand, Morton citrange and Swingle citrumelo seem to mask the effects of Flying Dragon interstock and did not show significant differences in vegetative growth between plants with and without interstock. Other researchers have reported that Volkamer lemon and Carrizo citrange neutralized the effect of Flying Dragon interstock on Hamlin sweet orange plants (Ferguson and Chaparro, 2004). Regarding cumulative yield, the rootstocks best suited to Tahiti lime scion were Catania 2 Volkamer lemon, 1646 and 1708 citradias, Orlando tangelo, and Morton citrange. Most of these rootstocks were classified as highly invigorating rootstocks, except on the citradias, which induced only intermediary vigor. Vigorous plants are grown in smaller densities at lower planting costs, but their high heights make pesticide applications and harvest labors difficult; thus, increasing operating costs. Less invigorating rootstocks have higher planting costs, but lower operating costs. Harvesting costs of dwarf plants are lower by avoiding the use of ladders (Tucker et al., 1994). Irrigation increased vegetative growth and fruit production. These results support previous research regarding the close relationship between the vegetative growth of young citrus plants and the irrigation regime (Shalhevet and Levy, 1990). Likewise, irrigated plants began to bear fruit earlier than plants without irrigation. Early-bearing is a highly valued attribute, especially in high density groves increasingly exposed to new phytosanitary problems raised in the last decade (Castle et al., 2010). Larger plants, however, resulted in lower production efficiency in the irrigated experiment, a fact that has also been observed on apples (Webster, 2004) and on mandarins (Mourão Filho et al., 2007). Based on their general performance, the evaluated rootstocks were classified according to their suitability for growth under irrigated or non-irrigated conditions. For non-irrigated groves, the most appropriate rootstocks were the Rangpur lime, Catania 2 Volkamer lemon, the 1646 and 1708 citradias, Morton citrange, and Orlando tangelo. Flying Dragon trifoliate also proved to be appropriate for non-irrigated conditions, although it is important to consider that in some seasons, the production on this rootstock may drop dramatically because of drought stress (Stuchi and Silva, 2005). Moreover, high density planting of Flying Dragon may lead to higher planting costs. Another important criterion for rootstock selection is their behavior concerning root rot caused by Phytophthora spp. In this study, several trees on Rangpur lime, Volkamer lemon, Orlando tangelo and SFS sour orange were lost due to root rot. The most suitable rootstocks for the irrigated plants were 1708 citradia, Morton citrange (not interstocked), Swingle citrumelo (interstocked) and Davis A trifoliate (interstocked). In general, irrigation also increased the yield in plants grafted on intermediate invigorating rootstocks and their cultivation should be considered only under this condition. On the other hand, irrigated trees budded on highly invigorating rootstocks did not significantly increase their yield. Irrigation increased plant vegetative growth, leading to a reduction in light interception and an increase in shading between trees that ultimately resulted in yields that were similar to nonirrigated plants. This information contradicts recommendations from other producing regions, such as Florida, where irrigation is an indispensable practice, even with an annual rainfall of about 1200 mm (Parson and Wheaton, 2000). However, in Florida, irriga-

6 E. Espinoza-Núñez et al. / Scientia Horticulturae 129 (2011) tion is crucial because the critical periods of flowering and fruit set occur during the dry season. In Brazil, these critical periods coincide with the onset of rain. However, in the São Paulo State, strong droughts and dry periods do frequently occur during flowering and initial fruit set stages, causing intense drop of flowers and developing fruits (Cantuarias-Avilés et al., 2010; Hutton et al., 2007). Rangpur lime induced higher yield when grown without irrigation. Irrigation increased vegetative growth and, consequently, decreased plant density. These results may explain, in part, the extensive choice of Rangpur lime in Brazil as rootstock for nonirrigated groves. However, this rootstock is very susceptible to root rot caused by Phytophthora spp. (Castle et al., 1993; Stenzel and Neves, 2004). Therefore, its use in recent years has decreased in Brazilian nurseries in favor of P. trifoliata hybrids (Pompeu and Blumer, 2006). In both experiments, plants budded on SFS sour orange and Orlando tangelo were the most susceptible to root rot, which caused the elimination of two treatments. Therefore, the use of both rootstocks is not recommended for Tahiti lime. These results are supported by studies showing that Orlando tangelo induces large plants and high yield, but it is highly susceptible to root rot (Figueiredo et al., 1996). The 1708 citradia outstood among all the studied rootstocks by inducing high yield, both on irrigated and non-irrigated conditions. Plants on this rootstock were intermediate-sized, with good quality fruit and had no symptoms of root rot susceptibility. The main criteria used in this study to select the rootstocks were yield, early-bearing, fruit quality, vigor, compatibility and tolerance to biotic and abiotic stresses. However, these criteria are insufficient if not coupled with economical aspects (Castle et al., 2010). In Tahiti lime, for instance, higher prices are paid for large dark-green fruits destined for export or for fruits picked in the off season (Gayet and Salvo Filho, 2003). 5. Conclusions - Flying Dragon trifoliate is a suitable rootstock for irrigated high density Tahiti lime groves. - The effect of rootstock on plant size and fruit yield can vary according to use of interstock. The Flying Dragon trifoliate used as interstock increases the yield of Tahiti lime grafted onto Davis A trifoliate and Swingle citrumelo, but reduces the yield of plants budded on Morton citrange. - Invigorating rootstocks grown without irrigation have high yields, with the 1646 citradia and the Morton citrange being strongly recommended for such conditions. - The rootstocks tetraploid Carrizo and Troyer citranges, Swingle citrumelo, and the trifoliates Davis A and Flying Dragon induced higher yields under irrigated conditions. - The 1708 citradia can be used as rootstock for irrigated or nonirrigated Tahiti lime, inducing high yields in both conditions. Acknowledgements The authors acknowledge Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) for the Ph.D. student fellowship to the first author (Proc. 07/ ) and grant support to this research. The authors also acknowledge Mr. Luiz Gustavo Parolin and Mr. Dimas Alves Toledo for technical support, and Dr. Jay L. 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