Performance of `Nova' mandarin on eleven
rootstocks in Cyprus
Androula Georgiou
*Agricultural Research Institute, PO Box 2016, Nicosia 1516, Cyprus
Accepted 18 August 1999
Abstract
Tree size, yield, yield ef®ciency, fruit quality and leaf nutrients of `Nova' mandarin (Citrus reticulataBlanco(C. paradisi Macf.C. reticulata)) on 11 rootstocks were evaluated under Cyprus conditions. Cumulative yield over the 11-year production period was highest on Palestine sweet lime rootstock (C. limettioidesTan.), followed by that on rough lemon (C. jambhiriLush.), sour orange (C. aurantiumL.), Volkamer lemon (C. volkamerianaTen. and Pasq.) and Estes rough lemon, although there were no signi®cant differences among these rootstocks. Cumulative yields on Carrizo and Yuma citranges (C. sinensiscv. Washington navelPoncirus trifoliata(L.) Raf.) were next in order, followed by those on Rangpur (C. limoniaObs.),C. taiwanica, Troyer citrange and Swingle citrumelo (C. paradisiMacf.P. trifoliata). The largest trees were on sour orange, rough lemon and Palestine sweet lime, and the smallest on Yuma and Carrizo citranges, Swingle citrumelo and Rangpur. Yield ef®ciency was highest on Carrizo citrange, whereas other rootstocks had similar yield ef®ciencies. Rootstock affected fruit size and weight, rind thickness, juice content, Brix, total acids and Brix:acid ratio. Leaf analysis showed signi®cant differences among rootstocks in the concentration of 10 out of 12 elements. Overall, results so for showed that Carrizo citrange and Volkamer lemon are the most promising for replacing the sour orange rootstocks which is used commercially in Cyprus but which is highly susceptible to tristeza.#2000 Elsevier Science B.V. All rights reserved.
Keywords: Yield; Canopy volume; Fruit quality
Scientia Horticulturae 84 (2000) 115±126
*
Tel.:352-2-305101; fax:357-2-316770.
E-mail address: [email protected] (A. Georgiou).
1. Introduction
`Nova' mandarin, a hybrid between `Fina' clementine and `Orlando' tangelo, is a relatively new crop in Cyprus, rapidly expanding during the last 2±3 years, as a result of the high demand in the export market due to its excellent fruit quality. `Nova' fruit are medium to large for a mandarin with an attractive high internal quality (Saunt, 1990). Being self-incompatible the fruit is seedless in isolation. However, it has ten or more seeds per fruit when cross-pollinated. `Nova' is widely grown in other Mediterranean countries such as Israel and Spain, where it is known as `Clemenvilla' and `Suntina', respectively.
In Cyprus, all citrus cultivars are mainly budded on sour orange, which is highly susceptible to tristeza (Wallace, 1956a,b; Salibe, 1973). The problem of tristeza in Cyprus (Papasolomontos and Economides, 1968; Kyriakou and Polycarpou, 1989) has necessitated a research program to replace the susceptible sour orange with rootstocks tolerant to tristeza, for almost all the commercial cultivars (Economides, 1976a,b, 1977; Economides and Gregoriou, 1993; Gregoriou and Economides, 1993, 1994; Georgiou and Gregoriou, 1998). The aim of this work was to evaluate the effect of 11 rootstocks on growth, yield, fruit quality and leaf mineral content of `Nova' mandarin.
2. Materials and methods
All rootstocks were propagated from seed. Seedlings were budded and trees were subsequently planted at the Citrus Experimental Station, Akhelia (Latitude, 358N; Longitude, 328E) in March 1984. Seeds were obtained from Willits and Newcomb, Arvin, CA, except those of sour orange and Palestine sweet lime, which were obtained locally from selected healthy trees. Budwood of `Nova' mandarin, free of all known pathogens, was imported from Willits and Newcomb in 1979. The experimental design was a randomized complete block with six replications and a single tree per plot. Tree spacing was 6.6 m4.2 m. The experimental plantation was not isolated but surrounded by various citrus cultivars such as `Clementine', `Ortanique', `Fortune', `Valencia' etc. Soil type, weather conditions and management have been previously described (Econo-mides and Gregoriou, 1993; Gregoriou and Econo(Econo-mides, 1993, 1994; Georgiou and Gregoriou, 1998).
In January 1997, height and canopy diameter and trunk circumference, 15 cm above the bud union, were measured. Canopy volume was calculated using the equation for one half of a prolate spheroid (Castle and Phillips, 1980) and trunk circumference was converted into trunk cross-sectional area (TCSA). Yield ef®ciency was estimated as the ratio of cumulative yield to canopy volume. Scion and stock circumference were measured in December, 1996 just above and below
the bud union and their ratio was determined. In September 1996, 30 leaves from non-fruiting twigs were collected from each tree and analyzed for N, P, K, Mg, Na, Ca, Mn, Zn, Cu, Fe and Cl by the following methods: Micro-Kjeldahl digestion for N, P, K, Na and colorimetric analysis of N and P with Chemlab Continuous Flow Analyzer; K and Na were analyzed on the ¯ame photometer. After ashing, samples were analyzed by atomic absorption for Ca, Mg, Fe, Mn, Cu and Zn. Chlorides were determined potentiometrically and Boron color-imetrically with carmine (Hatcher and Wilcox, 1950).
Fruit was harvested and weighed in the beginning of each year and 10 fruits per tree randomly collected, were analyzed for quality from 1988 to 1997. Fruits were weighed and fruit diameter and rind thickness at the equator were measured. Juice was extracted with a motor-driven hand reamer (Santos, No. 11) and Brix was measured with a hydrometer at 208C; total acids (TA) were determined (as citric acid equivalent) by titrating with NaOH (Anonymous, 1946). Data were analyzed using SAS procedures (SAS Institute, 1989). Analysis of variance was used to examine rootstock effects on yield and fruit quality characteristics. Means were separated by Duncan's New Multiple Range Test.
3. Results and discussion
3.1. Tree size
Rootstock had a signi®cant effect on TCSA, canopy diameter and canopy volume, but not on canopy height (Table 1). Rootstock in¯uence on canopy diameter was similar to that on canopy volume. Sour orange induced the highest values of canopy volume and canopy diameter, although they were not statistically different to those induced by Palestine sweet lime, rough lemon and Volkamer lemon. The smallest trees were those on Yuma citrange, Carrizo citrange and Swingle citrumelo, but they did not differ signi®cantly from those on Estes rough lemon, Rangpur, Troyer citrange andC. Taiwanica. TCSA is usually considered to be highly correlated with tree weight and canopy volume (Weestwood and Roberts, 1970). In this trial, the correlation between TCSA and canopy volume was moderately high and signi®cant (r0.56,P< 0.001).
3.2. Scion:stock ratio
The ratio of the circumference of the scion to that of the rootstock measures equality in growth rate of scion and rootstock (Roose et al., 1989). Swingle citrumelo, Yuma citrage and, to a lesser extent, Carrizo and Troyer citranges and
C. taiwanica tended to grow more rapidly than the scion (Table 1). The correlation coef®cient between scion:stock ratio and canopy volume was
moderately high and signi®cant (r0.42, P< 0.001). However, the correlation between scion:stock ratio and yield ef®ciency was low and negative (r ÿ0.28,
P< 0.003).
3.3. Yield
Trees on all rootstocks started bearing in 1987 at the age of 3 years. Trees on Palestine sweet lime had the highest cumulative yield, but not signi®cantly different from that on sour orange, rough lemon, Volkamer lemon and Estes rough lemon (Table 2). Trees on Swingle citrumelo and Troyer citrange were the least productive. The cumulative yield on Rangpur, Carrizo and Yuma citranges andC. taiwanicadid not differ signi®cantly, although they were more productive than Swingle citrumelo and Troyer citrange. Trees on all rootstocks exhibited a relatively strong alternate bearing index (ABI). However, no signi®cant differences were detected among the rootstocks.
3.4. Yield ef®ciency
Yield ef®ciency was highest on Carrizo citrange and lowest on sour orange, Troyer citrange and C. taiwanica (Table 2). However, yield ef®ciency on these rootstocks was not signi®cantly different from that on other rootstocks. The correlation between yield ef®ciency and tree volume was negative, high and
Table 1
Effect of rootstock on tree size and scion:stock ratio of `Nova' mandarin treesa
Rootstock Trunk
cross-Sour orange 184a 3.7a 4.08a 32.9a 0.88ab
Palestine sweet lime 146abc 3.7a 3.71abc 27.7abc 0.86abc
Rough lemon 145abc 3.7a 3.76ab 28.0ab 0.86abc
Estes rough lemon 138bc 3.4a 3.60bcd 23.6bcd 0.95a
Rangpur 110c 3.3a 3.38bcd 19.6cd 0.90a
Troyer citrange 140bc 3.5a 3.37bcd 21.4bcd 0.76bcd Carrizo citrange 139bc 3.4a 3.23cd 19.4cd 0.75cd
Yuma citrange 126bc 3.3a 3.20d 18.0d 0.67d
Swingle citrumelo 112c 3.3a 3.24cd 18.5d 0.65d
Volkamer lemon 167ab 3.7a 3.71abc 27.0abc 0.91a
C. taiwanica 153abc 3.5a 3.60bcd 24.0bcd 0.77bcd
cv. (%) 10 9 9 23 10
a
Means in the same column followed by different letters are signi®cantly different (p0.05) using Duncan's New Multiple Range test.
b
Ratio of scion trunk circumference to rootstock trunk circumference.
Table 2
Effect of rootstock on yield, yield ef®ciency (cumulative yield/tree volume) and alternate bearing index (ABI) of `Nova' mandarin treesa
Rootstock Yield (kg/tree) Yield efficiency
(kg mÿ3)
ABIb (%)
Year Cumulative
1987±1997
1993 1994 1995 1996 1997
Sour orange 11ab 150a 140ab 142abc 96abcd 1039ab 32.9b 23.1a
Palestine sweet lime 15a 136ab 148ab 149ab 92abcd 1156a 45.0ab 21.7a
Rough lemon 12ab 129abcd 154ab 162a 96abcd 1008a 36.9ab 22.1a
Estes rough lemon 12ab 127abcd 139ab 135abcd 84bcd 913abcd 38.3ab 24.7a
Rangpur 8b 95cd 109b 130abcd 107abc 751cd 38.3ab 22.7a
Troyer citrange 9b 198bcd 117b 99cd 137a 708d 33.1b 27.1a
Carrizo citrange 11ab 133abc 122b 117abcd 132ab 862bcd 49.5a 25.3a
Yuma citrange 10b 132abc 113b 93cd 100abcd 806bcd 45.2ab 26.7a
Swingle citrumelo 7b 90d 112b 89cd 80cd 673d 36.8ab 25.8a
Volkamer lemon 10b 136ab 180a 158a 112abc 988abc 36.9ab 24.3a
C. taiwanica 11ab 113abcd 109b 86d 53d 741cd 31.4b 27.1
cv. (%) 2 21 24 30 34 16 25 94
a
For explanation see footnote of Table 1.
b
ABI was calculated by dividing the difference between two successive crops by the sum of two successive crops100%.
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signi®cant (r ÿ0.51,P< 0.0001). Higher yield ef®ciencies were also reported for trees reduced in size by rootstocks (Castle and Phillips, 1980; Roose et al., 1989).
3.5. Fruit quality
Rootstock affected all fruit quality characteristics determined (Table 3). The largest and heaviest fruit was obtained on Volkamer lemon, Estes rough lemon, Rangpur and Troyer citrange; no rootstock induced smaller and lighter fruit than that induced by sour orange. However, the range in fruit weight and fruit diameter was less than 12% and 4%, respectively. Therefore, there is no practical signi®cance for the Cyprus industry, since the difference in commercial counts is ca. 18%. Differences in rind thickness, although signi®cant, were small. Fruit on Palestine sweet lime and Volkamer lemon had the thickest rind, whereas those on Troyer citrange the thinnest. Troyer and Yuma citranges produced fruit with the highest juice content, whereas Volkamer lemon and Rangpur the lowest. Most rootstocks induced fruit with lower Brix and acid content than those induced by sour orange. Only fruit on Troyer and Carrizo citranges had both Brix and acid content as high as on sour orange. The Brix:acid ratio was highest for C. taiwanicaand lowest for Volkamer lemon. Other rootstocks had similar Brix:acid ratio. Although the number of seeds per fruit was signi®cantly in¯uenced by the rootstocks, our observations did not reveal differences that could affect the market value of the fruit.
3.6. Leaf nutrient levels
Rootstock signi®cantly affected the nutrient level of 10 elements; differences in leaf concentration of Na and Fe were not signi®cant (Table 4). The N levels of `Nova' leaves were ``de®cient'' (Embleton et al., 1973) on sour orange, Estes rough lemon, rough lemon andC. taiwanica and in the low range on the other rootstocks. However, levels of N were highest on Carrizo citrange and Rangpur. These results con®rm those reported for various mandarin type scions, including `Nova' (Smith, 1975; Wutscher and Shull, 1976). The low levels of N may re¯ect the quantity and type of fertilizers applied. The P and K leaf levels were in the optimum or high ranges; the highest levels though were induced by Volkamer lemon and Swingle citrumelo. In this trial, N and K the two elements reportedly having the greatest effect on tree growth (Smith et al., 1970) were not signi®cantly correlated with TCSA and tree volume.
Leaf levels of Mg, Na and Ca were in the optimum range, on almost all rootstocks. Rootstock effects on Mg levels were strong, in that Carrizo and Troyer citranges accumulated the highest and Estes rough lemon and Palestine sweet lime the lowest levels of Mg. These results are in agreement with those reported
Table 3
Effect of rootstock on `Nova' mandarin quality (Average 1987±1997)a
Rootstock Fruit
Sour orange 132.8d 6.67d 3.13cd 53.19abc 12.22cd 1.01a 12.04bcd 11.8 ab
Palestine sweet lime 140.7bc 6.79abcd 3.63a 51.96bcd 11.24d 0.96b 11.84cd 14.8 a Rough lemon 139.8bc 6.79abcd 3.52ab 51.86bcd 11.08de 0.93bc 11.98bcd 11.4ab
Estes rough lemon 141.7b 6.88a 3.56ab 51.45d 10.94e 0.90 12.04bcd 13.7a
Rangpur 141.4b 6.82ab 3.27cd 49.44e 11.31d 0.93bc 12.26b 12.2ab
Troyer citrange 141.7b 6.81abc 3.06d 54.17a 12.13abc 1.02a 11.93bcd 12.0ab
Carrizo citrange 137.5bcd 6.77abcd 3.13cd 52.04bcd 12.35a 1.01a 12.19bc 9.1b
Yuma citrange 135.2cd 6.69cd 3.33bc 53.29ab 11.96c 1.01a 11.84cd 10.5ab
Swingle citrumelo 139.8bc 6.81abc 3.26cd 52.92abcd 11.88c 1.05a 11.36e 11.2ab
Volkamer lemon 148.3a 6.87ab 3.58a 49.87e 10.82c 0.92bc 11.74d 12.4ab
C. taiwanica 137.8bcd 6.75bcd 3.20cd 51.50cd 11.30d 0.90c 12.63a 13.2ab
cv. (%) 8 3 13 6 4 7 5 24
aFor explanation see footnote of Table 1.
Table 4
Effect of rootstock on leaf composition of `Nova' mandarina
Rootstock N
Sour orange 1.99d 0.103d 1.04cd 0.31bc 0.12a 6.23a 27.5ef 17.8bcd 11.8abc 197a 108c 730bcd Palestine sweet lime 2.25ab 0.115cd 1.23bc 0.24e 0.14a 5.54bc 48.0a 26.8a 7.4e 173a 142b 750abcd Rough lemon 2.12bcd 0.125abc 1.24b 0.26de 0.13a 5.22cd 35.0bcd 24.5a 9.4cde 172a 118bc 550d Estes rough lemon 2.11bcd 0.118bcd 1.13bcd 0.23e 0.17a 5.53bc 40.0b 19.3bcd 10.9bcd 165a 130bc 840abc Rangpur 2.26ab 0.133ab 1.19bcd 0.28cd 0.14a 5.28cd 36.7bc 19.7b 13.3ab 156a 118bc 640cd Troyer citrange 2.17bcd 0.126abc 1.03d 0.38a 0.13a 5.20cd 26.3f 15.8d 14.5a 180a 141b 820abcd Carrizo citrange 2.38a 0.120abc 1.08bcd 0.39a 0.16a 5.25cd 27.8ef 16.0cd 14.3ab 193a 114bc 950ab Yuma citrange 2.23abc 0.130abc 1.21bcd 0.30bc 0.14a 5.39c 33.8bcde 17.8bcd 13.0ab 158a 174a 880abc Swingle citrumelo 2.17cd 0.135a 1.44a 0.30bc 0.14a 5.13cd 34.0bcde 19.5bc 14.5a 134a 113bc 1003a Volkamer lemon 2.18bcd 0.133ab 1.52a 0.24e 0.14a 4.72d 32.8cdef 20.8b 10.9bcd 150a 119bc 680cd
C. taiwanica 2.06cd 0.125abc 1.18bcd 0.33b 0.15a 6.03ab 30.0def 21.0b 8.2de 199a 172a 730bcd
cv. (%) 5.12 8.06 9.37 7.26 17.84 7.30 11.90 10.89 18.45 19.31 14.04 21.99
a
For explanation see footnote of Table 1.
by Smith (1975) and by Castle and Krezdorn (1975). The well-known K/Mg antagonism (Embleton et al., 1973) is strongly expressed by Volkamer lemon and Palestine sweet lime and to a lesser degree by Estes rough lemon, Swingle citrumelo and rough lemon. Effects of rootstocks on Mn, Zn and Cu levels were particularly pronounced, with Cu content being in¯uenced the most. On all rootstocks, levels of Mn and Cu were in the normal range whereas those of Zn were in the low range on all except one rootstock. In Cyprus, Zn de®ciencies are common because of the high pH. It seems that foliar Zn sprays cannot be avoided with the selection of rootstock.
Selection of rootstock is an important mean of avoiding Cl and B toxicities, and Fe de®ciency chlorosis in adverse soil conditions (Embleton et al., 1973; Taylor and Dimsey, 1993). In the current trial rootstock strongly in¯uenced the B and Cl leaf levels but not Fe levels. Levels of Fe and B were in the high range whereas those of Cl in the normal range. Despite the fact the soil in this experiment has a relatively high lime content (20%) and a high pH (8.0), trees on all rootstocks except those on Yuma citrange did not become chlorotic, probably because of the high Fe and adequate Mg leaf levels (Mikhail and El-Zeftawi, 1979). Levels of B and Cl were in the high and normal range, respectively. Yuma citrange and C. taiwanicaaccumulated the highest and sour the lowest B level.
Rough lemon and Rangpur showed the lowest Cl levels, which concurs with reports that these rootstocks are good excluder of Cl which make them tolerant to high salinity (Taylor and Dimsey, 1993). In contrast, Swingle citrumelo and citranges are accumulators of Cl although the levels were not in toxic range.
It is obvious that rootstocks have a strong effect on the mineral nutrition of `Nova' trees. However, it is emphasized that nutritional effects of rootstocks can be in¯uenced by edaphoclimatic conditions and cultural practices (Sharples and Hilgeman, 1972).
3.7. Promising rootstocks
Based on the present results, Carrizo citrange and Volkamer lemon, both tolerant to tristeza, appear to be the most promising. Both rootstocks had a similar cumulative yield to that of sour orange. Moreover, Carrizo citrange had a signi®cantly higher yield ef®ciency and lower tree volume. These characteristics suggest that it may also be suitable for a higher planting density.
Fruit quality on Carrizo citrange was high and similar to that on sour orange. Fruit on Volkamer lemon was the heaviest, and among the largest, but with juice, Brix and acid content signi®cantly lower than that on sour orange. Differences in these organoleptic characteristics, although signi®cant are still small and are not expected to affect the market value of the fruit.
This experimental work took place in an area where the soil contained 20% CaCO3. However, the most citrus producing areas in Cyprus are highly
calcareous. Since Carrizo citrange is sensitive to highly calcareous soils in these areas Volkamer lemon should be preferred because of its high calcium tolerance. (Wutscher, 1979; Roose, 1990; Davies and Albrigo, 1994).
Rough lemon, Estes rough lemon, Palestine sweet lime and Rangpur are not considered promising, mainly because of their sensitivity to diseases. All of them are highly susceptible to Phytophthora (Whiteside and Knorr, 1978; Wutscher, 1979; Roose, 1990; Timmer et al., 1991; Davies and Albrigo, 1994), whereas regarding their reaction to tristeza, Palestine sweet lime is moderately susceptible and rough lemon susceptible to the severe strains of the virus (Wutscher, 1979; Davies and Albrigo, 1994).
The other two citranges evaluated, Troyer and Yuma, are not as good as Carrizo. Compared with Carrizo, Troyer decreased cumulative yield and yield ef®ciency by 18% and 33%, respectively, whereas it increased tree volume by 10%. Trees on Yuma citrange, as well as being chlorotic, exhibited a very low ratio of scion:stock circumference which may indicate bud union problems in the future. In addition, Yuma signi®cantly reduced Brix content. Swingle citrumelo and C. taiwanica were the least productive rootstocks considering both cumulative yield and yield ef®ciency. In addition, Swingle citrumelo showed the lowest scion:stock ratio.
In conclusion, the results of this experiment show that tree size, yield, yield ef®ciency and fruit quality of `Nova' mandarin can be controlled by the proper selection of rootstock and that Carrizo citrange and Volkamer lemon seem to be the most promising in replacing the tristeza Ð susceptible sour orange in Cyprus. However, this trial is young and conclusions may be altered as disease problems and incompatibilities often become more evident as trees age.
Acknowledgements
The author wishes to thank Mr C.V. Economides for running the experiment until 1987, Mr C. Cregoriou for supervising the experiment from 1987 to 1992, Dr. A. Mavrogenis for statistical analysis and Mr N. Karaolis, Mr G. Kallis and Mrs A. Argyridou for technical assistance.
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