Directory UMM :Data Elmu:jurnal:S:Scientia Horticulturae:Vol84.Issue1-2.Apr2000:
Scientia Horticulturae 84 (2000) 115±126
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
reticulata Blanco (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. limettioides Tan.), followed by that on rough lemon (C. jambhiri Lush.),
sour orange (C. aurantium L.), Volkamer lemon (C. volkameriana Ten. and Pasq.) and Estes rough
lemon, although there were no signi®cant differences among these rootstocks. Cumulative yields on
Carrizo and Yuma citranges (C. sinensis cv. Washington navel Poncirus trifoliata (L.) Raf.) were
next in order, followed by those on Rangpur (C. limonia Obs.), C. taiwanica, Troyer citrange and
Swingle citrumelo (C. paradisi Macf. 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
*
Tel.: 352-2-305101; fax: 357-2-316770.
E-mail address: [email protected] (A. Georgiou).
0304-4238/00/$ ± see front matter # 2000 Elsevier Science B.V. All rights reserved.
PII: S 0 3 0 4 - 4 2 3 8 ( 9 9 ) 0 0 1 2 0 - X
116
A. Georgiou / Scientia Horticulturae 84 (2000) 115±126
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 m 4.2 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 (Economides and Gregoriou, 1993; Gregoriou and Economides, 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
A. Georgiou / Scientia Horticulturae 84 (2000) 115±126
117
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 colorimetrically 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 and C. 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 (r 0.56, 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
118
A. Georgiou / Scientia Horticulturae 84 (2000) 115±126
Table 1
Effect of rootstock on tree size and scion:stock ratio of `Nova' mandarin treesa
Rootstock
Trunk cross- Canopy
sectional area height
(cm2)
(m)
Canopy
diameter
(m)
Canopy
volume
(m3)
Scion:stock
ratiob
Sour orange
Palestine sweet lime
Rough lemon
Estes rough lemon
Rangpur
Troyer citrange
Carrizo citrange
Yuma citrange
Swingle citrumelo
Volkamer lemon
C. taiwanica
cv. (%)
184a
146abc
145abc
138bc
110c
140bc
139bc
126bc
112c
167ab
153abc
10
4.08a
3.71abc
3.76ab
3.60bcd
3.38bcd
3.37bcd
3.23cd
3.20d
3.24cd
3.71abc
3.60bcd
9
32.9a
27.7abc
28.0ab
23.6bcd
19.6cd
21.4bcd
19.4cd
18.0d
18.5d
27.0abc
24.0bcd
23
0.88ab
0.86abc
0.86abc
0.95a
0.90a
0.76bcd
0.75cd
0.67d
0.65d
0.91a
0.77bcd
10
3.7a
3.7a
3.7a
3.4a
3.3a
3.5a
3.4a
3.3a
3.3a
3.7a
3.5a
9
a
Means in the same column followed by different letters are signi®cantly different (p 0.05)
using Duncan's New Multiple Range test.
b
Ratio of scion trunk circumference to rootstock trunk circumference.
moderately high and signi®cant (r 0.42, 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
and C. taiwanica did 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 2
Effect of rootstock on yield, yield ef®ciency (cumulative yield/tree volume) and alternate bearing index (ABI) of `Nova' mandarin treesa
Yield (kg/tree)
Year
Sour orange
Palestine sweet lime
Rough lemon
Estes rough lemon
Rangpur
Troyer citrange
Carrizo citrange
Yuma citrange
Swingle citrumelo
Volkamer lemon
C. taiwanica
cv. (%)
a
b
Yield efficiency
(kg mÿ3)
ABIb
(%)
32.9b
45.0ab
36.9ab
38.3ab
38.3ab
33.1b
49.5a
45.2ab
36.8ab
36.9ab
31.4b
25
23.1a
21.7a
22.1a
24.7a
22.7a
27.1a
25.3a
26.7a
25.8a
24.3a
27.1
94
Cumulative
1987±1997
1993
1994
1995
1996
1997
11ab
15a
12ab
12ab
8b
9b
11ab
10b
7b
10b
11ab
2
150a
136ab
129abcd
127abcd
95cd
198bcd
133abc
132abc
90d
136ab
113abcd
21
140ab
148ab
154ab
139ab
109b
117b
122b
113b
112b
180a
109b
24
142abc
149ab
162a
135abcd
130abcd
99cd
117abcd
93cd
89cd
158a
86d
30
96abcd
92abcd
96abcd
84bcd
107abc
137a
132ab
100abcd
80cd
112abc
53d
34
1039ab
1156a
1008a
913abcd
751cd
708d
862bcd
806bcd
673d
988abc
741cd
16
A. Georgiou / Scientia Horticulturae 84 (2000) 115±126
Rootstock
For explanation see footnote of Table 1.
ABI was calculated by dividing the difference between two successive crops by the sum of two successive crops 100%.
119
120
A. Georgiou / Scientia Horticulturae 84 (2000) 115±126
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.
taiwanica and 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 and C. 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
Fruit
weight
(g)
Fruit
diameter
(cm)
Rind
thickness
(mm)
Juice
content
(%)
Brix
(%)
Total acids
(TA) (%)
Brix:TA
ratio
Number
of seeds
per fruit
Sour orange
Palestine sweet lime
Rough lemon
Estes rough lemon
Rangpur
Troyer citrange
Carrizo citrange
Yuma citrange
Swingle citrumelo
Volkamer lemon
C. taiwanica
cv. (%)
132.8d
140.7bc
139.8bc
141.7b
141.4b
141.7b
137.5bcd
135.2cd
139.8bc
148.3a
137.8bcd
8
6.67d
6.79abcd
6.79abcd
6.88a
6.82ab
6.81abc
6.77abcd
6.69cd
6.81abc
6.87ab
6.75bcd
3
3.13cd
3.63a
3.52ab
3.56ab
3.27cd
3.06d
3.13cd
3.33bc
3.26cd
3.58a
3.20cd
13
53.19abc
51.96bcd
51.86bcd
51.45d
49.44e
54.17a
52.04bcd
53.29ab
52.92abcd
49.87e
51.50cd
6
12.22cd
11.24d
11.08de
10.94e
11.31d
12.13abc
12.35a
11.96c
11.88c
10.82c
11.30d
4
1.01a
0.96b
0.93bc
0.90
0.93bc
1.02a
1.01a
1.01a
1.05a
0.92bc
0.90c
7
12.04bcd
11.84cd
11.98bcd
12.04bcd
12.26b
11.93bcd
12.19bc
11.84cd
11.36e
11.74d
12.63a
5
11.8 ab
14.8 a
11.4ab
13.7a
12.2ab
12.0ab
9.1b
10.5ab
11.2ab
12.4ab
13.2ab
24
a
For explanation see footnote of Table 1.
A. Georgiou / Scientia Horticulturae 84 (2000) 115±126
Rootstock
121
122
Rootstock
N
(%)
P
(%)
K
(%)
Mg
(%)
Na
(%)
Ca
(%)
Mn
(ppm)
Zn
(ppm)
Cu
(ppm)
Fe
(ppm)
B
(ppm)
Cl
(ppm)
Sour orange
Palestine sweet lime
Rough lemon
Estes rough lemon
Rangpur
Troyer citrange
Carrizo citrange
Yuma citrange
Swingle citrumelo
Volkamer lemon
C. taiwanica
cv. (%)
1.99d
2.25ab
2.12bcd
2.11bcd
2.26ab
2.17bcd
2.38a
2.23abc
2.17cd
2.18bcd
2.06cd
5.12
0.103d
0.115cd
0.125abc
0.118bcd
0.133ab
0.126abc
0.120abc
0.130abc
0.135a
0.133ab
0.125abc
8.06
1.04cd
1.23bc
1.24b
1.13bcd
1.19bcd
1.03d
1.08bcd
1.21bcd
1.44a
1.52a
1.18bcd
9.37
0.31bc
0.24e
0.26de
0.23e
0.28cd
0.38a
0.39a
0.30bc
0.30bc
0.24e
0.33b
7.26
0.12a
0.14a
0.13a
0.17a
0.14a
0.13a
0.16a
0.14a
0.14a
0.14a
0.15a
17.84
6.23a
5.54bc
5.22cd
5.53bc
5.28cd
5.20cd
5.25cd
5.39c
5.13cd
4.72d
6.03ab
7.30
27.5ef
48.0a
35.0bcd
40.0b
36.7bc
26.3f
27.8ef
33.8bcde
34.0bcde
32.8cdef
30.0def
11.90
17.8bcd
26.8a
24.5a
19.3bcd
19.7b
15.8d
16.0cd
17.8bcd
19.5bc
20.8b
21.0b
10.89
11.8abc
7.4e
9.4cde
10.9bcd
13.3ab
14.5a
14.3ab
13.0ab
14.5a
10.9bcd
8.2de
18.45
197a
173a
172a
165a
156a
180a
193a
158a
134a
150a
199a
19.31
108c
142b
118bc
130bc
118bc
141b
114bc
174a
113bc
119bc
172a
14.04
730bcd
750abcd
550d
840abc
640cd
820abcd
950ab
880abc
1003a
680cd
730bcd
21.99
a
For explanation see footnote of Table 1.
A. Georgiou / Scientia Horticulturae 84 (2000) 115±126
Table 4
Effect of rootstock on leaf composition of `Nova' mandarina
A. Georgiou / Scientia Horticulturae 84 (2000) 115±126
123
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.
taiwanica accumulated 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
124
A. Georgiou / Scientia Horticulturae 84 (2000) 115±126
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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grapefruit on 15 rootstocks in Cyprus. J. Am. Soc. Hort. Sci. 118(3), 326±329.
Embleton, T.W., Jones, W.W., Labanauskas, C.K., Reuther, W., 1973. Leaf analysis as a diagnostic
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California Press, Berkeley, CA, pp. 184±210.
Georgiou, A., Gregoriou, C., 1998. Yield and fruit quality of `Shamouti' orange on 14 rootstocks in
Cyprus. Sci. Hort. 1307, 1±10.
Gregoriou, C., Economides, C.V., 1993. Growth, yield, and fruit quality of nucellar frost Marsh
grapefruit on 15 rootstocks in Cyprus. J. Am. Soc. Hort. Sci. 118(3), 326±329.
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orange on 15 rootstocks in Cyprus. Acta Hort. 365, 57±68.
Hatcher, J.Y., Wilcox, L.V., 1950. Colorimetric determination of boron using carmine. Anal. Chem.
22, 567±569.
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Improvement Council, News 12, pp. 3±4.
Mikhail, E.H., El-Zeftawi, B.M., 1979. Effect of soil types and rootstocks on root distribution,
chemical composition of leaves and yield of Valencia oranges. Aus. J. Soil Res. 17, 335±342.
Papasolomontos, A., Economides, C.V., 1968. The presence of tristeza virus in certain species of
citrus in Cyprus. FAO Plant Protection Bull. 16, 8±9.
Roose, M.L., 1990. California citrus rootstocks. Div. of Agric. and Nat. Res., University of
California, Publication 21477.
Roose, M.L., Cole, P.A., Atkin, D., Kupper, R.S., 1989. Yield and tree size of four citrus cultivars
on 21 rootstocks in California. J. Am. Soc. Hort. Sci. 114(4), 678±684.
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Saunt, J., 1990. Citrus varieties of the world. Singlair International, UK.
Sharples, G.C., Hilgeman, 1972. Leaf mineral composition of ®ve citrus cultivars grown on sour
orange and rough lemon rootstocks. J. Am. Soc. Hort. Sci., 97(3), 427±430.
Smith, P.F., 1975. Effect of scion and rootstock on mineral composition of mandarin-type citrus
leaves. J. Am. Soc. Hort. Sci. 100, 368±369.
Smith, G.K., Scudder Jr., Hrnciar, G., 1970. Comparison of four varieties of young- and oldbudline oranges grown on sand culture with three potassium levels. Proc. Fla. State Hort. Soc.
83, 6±10.
Taylor, B.K., Dimsey, R.T., 1993. Rootstock and scion effects on the leaf nutrient composition of
citrus trees. Aus. J. Expt. Agric. 33, 363±371.
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phytophthora root rot and populations of phytophthora paracitica. Proc. Fla. State Hort. Soc.
104, 173±178.
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Wallace, J.M., 1956a. Tristeza disease of citrus with special reference to its situation in the US. FAO
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Wallace, J.M., 1956b. Tristeza and stem-pitting disease of citrus in South Africa. FAO Plant
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Whiteside, J.O., Knorr, L.C., 1978. Susceptibility of different rough lemon collections to foot rot
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Hort. Sci. 101(1), 88±91.
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
reticulata Blanco (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. limettioides Tan.), followed by that on rough lemon (C. jambhiri Lush.),
sour orange (C. aurantium L.), Volkamer lemon (C. volkameriana Ten. and Pasq.) and Estes rough
lemon, although there were no signi®cant differences among these rootstocks. Cumulative yields on
Carrizo and Yuma citranges (C. sinensis cv. Washington navel Poncirus trifoliata (L.) Raf.) were
next in order, followed by those on Rangpur (C. limonia Obs.), C. taiwanica, Troyer citrange and
Swingle citrumelo (C. paradisi Macf. 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
*
Tel.: 352-2-305101; fax: 357-2-316770.
E-mail address: [email protected] (A. Georgiou).
0304-4238/00/$ ± see front matter # 2000 Elsevier Science B.V. All rights reserved.
PII: S 0 3 0 4 - 4 2 3 8 ( 9 9 ) 0 0 1 2 0 - X
116
A. Georgiou / Scientia Horticulturae 84 (2000) 115±126
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 m 4.2 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 (Economides and Gregoriou, 1993; Gregoriou and Economides, 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
A. Georgiou / Scientia Horticulturae 84 (2000) 115±126
117
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 colorimetrically 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 and C. 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 (r 0.56, 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
118
A. Georgiou / Scientia Horticulturae 84 (2000) 115±126
Table 1
Effect of rootstock on tree size and scion:stock ratio of `Nova' mandarin treesa
Rootstock
Trunk cross- Canopy
sectional area height
(cm2)
(m)
Canopy
diameter
(m)
Canopy
volume
(m3)
Scion:stock
ratiob
Sour orange
Palestine sweet lime
Rough lemon
Estes rough lemon
Rangpur
Troyer citrange
Carrizo citrange
Yuma citrange
Swingle citrumelo
Volkamer lemon
C. taiwanica
cv. (%)
184a
146abc
145abc
138bc
110c
140bc
139bc
126bc
112c
167ab
153abc
10
4.08a
3.71abc
3.76ab
3.60bcd
3.38bcd
3.37bcd
3.23cd
3.20d
3.24cd
3.71abc
3.60bcd
9
32.9a
27.7abc
28.0ab
23.6bcd
19.6cd
21.4bcd
19.4cd
18.0d
18.5d
27.0abc
24.0bcd
23
0.88ab
0.86abc
0.86abc
0.95a
0.90a
0.76bcd
0.75cd
0.67d
0.65d
0.91a
0.77bcd
10
3.7a
3.7a
3.7a
3.4a
3.3a
3.5a
3.4a
3.3a
3.3a
3.7a
3.5a
9
a
Means in the same column followed by different letters are signi®cantly different (p 0.05)
using Duncan's New Multiple Range test.
b
Ratio of scion trunk circumference to rootstock trunk circumference.
moderately high and signi®cant (r 0.42, 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
and C. taiwanica did 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 2
Effect of rootstock on yield, yield ef®ciency (cumulative yield/tree volume) and alternate bearing index (ABI) of `Nova' mandarin treesa
Yield (kg/tree)
Year
Sour orange
Palestine sweet lime
Rough lemon
Estes rough lemon
Rangpur
Troyer citrange
Carrizo citrange
Yuma citrange
Swingle citrumelo
Volkamer lemon
C. taiwanica
cv. (%)
a
b
Yield efficiency
(kg mÿ3)
ABIb
(%)
32.9b
45.0ab
36.9ab
38.3ab
38.3ab
33.1b
49.5a
45.2ab
36.8ab
36.9ab
31.4b
25
23.1a
21.7a
22.1a
24.7a
22.7a
27.1a
25.3a
26.7a
25.8a
24.3a
27.1
94
Cumulative
1987±1997
1993
1994
1995
1996
1997
11ab
15a
12ab
12ab
8b
9b
11ab
10b
7b
10b
11ab
2
150a
136ab
129abcd
127abcd
95cd
198bcd
133abc
132abc
90d
136ab
113abcd
21
140ab
148ab
154ab
139ab
109b
117b
122b
113b
112b
180a
109b
24
142abc
149ab
162a
135abcd
130abcd
99cd
117abcd
93cd
89cd
158a
86d
30
96abcd
92abcd
96abcd
84bcd
107abc
137a
132ab
100abcd
80cd
112abc
53d
34
1039ab
1156a
1008a
913abcd
751cd
708d
862bcd
806bcd
673d
988abc
741cd
16
A. Georgiou / Scientia Horticulturae 84 (2000) 115±126
Rootstock
For explanation see footnote of Table 1.
ABI was calculated by dividing the difference between two successive crops by the sum of two successive crops 100%.
119
120
A. Georgiou / Scientia Horticulturae 84 (2000) 115±126
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.
taiwanica and 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 and C. 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
Fruit
weight
(g)
Fruit
diameter
(cm)
Rind
thickness
(mm)
Juice
content
(%)
Brix
(%)
Total acids
(TA) (%)
Brix:TA
ratio
Number
of seeds
per fruit
Sour orange
Palestine sweet lime
Rough lemon
Estes rough lemon
Rangpur
Troyer citrange
Carrizo citrange
Yuma citrange
Swingle citrumelo
Volkamer lemon
C. taiwanica
cv. (%)
132.8d
140.7bc
139.8bc
141.7b
141.4b
141.7b
137.5bcd
135.2cd
139.8bc
148.3a
137.8bcd
8
6.67d
6.79abcd
6.79abcd
6.88a
6.82ab
6.81abc
6.77abcd
6.69cd
6.81abc
6.87ab
6.75bcd
3
3.13cd
3.63a
3.52ab
3.56ab
3.27cd
3.06d
3.13cd
3.33bc
3.26cd
3.58a
3.20cd
13
53.19abc
51.96bcd
51.86bcd
51.45d
49.44e
54.17a
52.04bcd
53.29ab
52.92abcd
49.87e
51.50cd
6
12.22cd
11.24d
11.08de
10.94e
11.31d
12.13abc
12.35a
11.96c
11.88c
10.82c
11.30d
4
1.01a
0.96b
0.93bc
0.90
0.93bc
1.02a
1.01a
1.01a
1.05a
0.92bc
0.90c
7
12.04bcd
11.84cd
11.98bcd
12.04bcd
12.26b
11.93bcd
12.19bc
11.84cd
11.36e
11.74d
12.63a
5
11.8 ab
14.8 a
11.4ab
13.7a
12.2ab
12.0ab
9.1b
10.5ab
11.2ab
12.4ab
13.2ab
24
a
For explanation see footnote of Table 1.
A. Georgiou / Scientia Horticulturae 84 (2000) 115±126
Rootstock
121
122
Rootstock
N
(%)
P
(%)
K
(%)
Mg
(%)
Na
(%)
Ca
(%)
Mn
(ppm)
Zn
(ppm)
Cu
(ppm)
Fe
(ppm)
B
(ppm)
Cl
(ppm)
Sour orange
Palestine sweet lime
Rough lemon
Estes rough lemon
Rangpur
Troyer citrange
Carrizo citrange
Yuma citrange
Swingle citrumelo
Volkamer lemon
C. taiwanica
cv. (%)
1.99d
2.25ab
2.12bcd
2.11bcd
2.26ab
2.17bcd
2.38a
2.23abc
2.17cd
2.18bcd
2.06cd
5.12
0.103d
0.115cd
0.125abc
0.118bcd
0.133ab
0.126abc
0.120abc
0.130abc
0.135a
0.133ab
0.125abc
8.06
1.04cd
1.23bc
1.24b
1.13bcd
1.19bcd
1.03d
1.08bcd
1.21bcd
1.44a
1.52a
1.18bcd
9.37
0.31bc
0.24e
0.26de
0.23e
0.28cd
0.38a
0.39a
0.30bc
0.30bc
0.24e
0.33b
7.26
0.12a
0.14a
0.13a
0.17a
0.14a
0.13a
0.16a
0.14a
0.14a
0.14a
0.15a
17.84
6.23a
5.54bc
5.22cd
5.53bc
5.28cd
5.20cd
5.25cd
5.39c
5.13cd
4.72d
6.03ab
7.30
27.5ef
48.0a
35.0bcd
40.0b
36.7bc
26.3f
27.8ef
33.8bcde
34.0bcde
32.8cdef
30.0def
11.90
17.8bcd
26.8a
24.5a
19.3bcd
19.7b
15.8d
16.0cd
17.8bcd
19.5bc
20.8b
21.0b
10.89
11.8abc
7.4e
9.4cde
10.9bcd
13.3ab
14.5a
14.3ab
13.0ab
14.5a
10.9bcd
8.2de
18.45
197a
173a
172a
165a
156a
180a
193a
158a
134a
150a
199a
19.31
108c
142b
118bc
130bc
118bc
141b
114bc
174a
113bc
119bc
172a
14.04
730bcd
750abcd
550d
840abc
640cd
820abcd
950ab
880abc
1003a
680cd
730bcd
21.99
a
For explanation see footnote of Table 1.
A. Georgiou / Scientia Horticulturae 84 (2000) 115±126
Table 4
Effect of rootstock on leaf composition of `Nova' mandarina
A. Georgiou / Scientia Horticulturae 84 (2000) 115±126
123
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.
taiwanica accumulated 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
124
A. Georgiou / Scientia Horticulturae 84 (2000) 115±126
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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