Olinda Valencia’ Trees Grown on Nine Rootstocks in Saudi Arabia

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Obreza, T. A. 1994. Program fertilization for densely-planted ‘Hamlin’ or- Tucker, D. P. H., A. K. Alva, L. K. Jackson, and T. A. Wheaton. 1995. Nutrition ange trees. Proc. Fla. State Hort. Soc. 107:47-50. of Florida citrus trees. Univ. of Fla. Coop. Ext. Ser. SP 169, Gainesville. Rasmussen, G. K. and P. F. Smith. 1961. Evaluation of fertilizer practices for Willis, L. E., F. S. Davies, and D. A. Graetz. 1990. Fertilization, nitrogen leach- young orange trees. Proc. Fla. State Hort. Soc. 74:90-95. ing and growth of young Hamlin orange trees on two rootstocks. Proc. Syvertsen, J. P. and M. L. Smith. 1996. Nitrogen uptake efficiency and leach- Fla. State Hort. Soc. 103:30-37. ing losses from lysimeter-grown citrus trees fertilized at 3 nitrogen rates. Wutscher, H. K. 1989. Alteration of fruit tree nutrition through rootstocks. J. Amer. Soc. Hort. Sci. 121:57-62. HortScience 24:578-584.

Proc. Fla. State Hort. Soc. 115:17-22. 2002. YIELD AND FRUIT QUALITY OF ‘OLINDA VALENCIA’ TREES GROWN ON NINE ROOTSTOCKS IN SAUDI ARABIA

ALI AL-JALEEL bia, comprises 25% of total citrus production area. There are Najran Horticulture Development Research Center over one million trees and over 1,000 citrus orchards in the Ministry of Agriculture & Water, Food & Agriculture Organization Najran area. Orchard size ranges from one to 50 ha. In the Najran, Kingdom of Saudi Arabia Kingdom of Saudi Arabia, fruit is not sold based on soluble solids. All fruit is marketed fresh by weight and consumed lo- MONGI ZEKRI1 cally (Zekri and Al-Jaleel, 2000). University of Florida, IFAS ‘Clementine’ mandarin and Parent ‘Washington’ navel Hendry County Extension Office orange were among the most popular citrus cultivars grown PO Box 68 in the Najran area. However, because of the shortage of irri- LaBelle, FL 33935-0068 gation water, rainfall, and frequency of droughts, granulation (the drying of juice sacs of the fruit) has become a serious Additional index words. citrus, fruit production, fruit size, solu- problem for those two cultivars. Therefore, for the last five ble solids years, planting these cultivars has not been recommended. Currently, the most popular sweet orange cultivar in the King- dom of Saudi Arabia is ‘Olinda Valencia’, which accounts for Abstract. A long-term study was carried out to evaluate the horticultural adaptability and performance of ‘Olinda Valencia’ 30% of all citrus (Zekri and Al-Jaleel, 2000). sweet orange trees on nine commercial rootstocks in the Naj- Fifteen years ago, the most popular rootstocks, in the Naj- ran area of Saudi Arabia. Fruit yield, fruit size, individual fruit ran area of Saudi Arabia, were sour orange, ‘Troyer’ and ‘Carr- weight, peel thickness, percent juice, soluble solids, and acids izo’. Because of increasing problems with high pH and salinity, were measured. Over the seven-year production period, trees rootstocks have become a more critical issue than in previous on rough lemon (RL), ‘Volkamer’ lemon (VL), and Citrus mac- years. ‘Volkamer’ lemon, macrophylla, and ‘Cleopatra’ manda- rophylla (CM) were the most productive and trees on ‘Swingle’ rin have been gaining ground and are becoming very popular. citrumelo (SC) and ‘Cleopatra’ mandarin (Cleo) were the least Rootstocks have had a substantial role in the development productive. Trees on sour orange (SO), ‘Carrizo’ citrange (CC), of the citrus industry in the world. The effect of rootstocks on Citrus Taiwanica (CT), and Amblycarpa (Amb) were intermedi- ate in fruit production. The greatest fruit individual weight and citrus fruit production and fruit quality has been intensively largest fruit were found on trees budded on VL and CM, while studied in many citrus producing areas (Continella et al., the lowest fruit weight and smallest fruit were found on trees 1988; Economides and Gregorion, 1993; Fallahi and Rodney, budded on Cleo and SO. Trees on SC had the highest juice 1992; Fallahi et al., 1989; Gardner and Horanic, 1961, 1966; content and those on RL had the lowest juice content. Fruit Grisoni et al., 1989; Monteverde et al., 1988; Roose et al., 1989; from trees on CC accumulated the highest soluble solids and Rouse and Maxwell, 1979; Wheaton et al., 1991; Zekri, 1996, fruit from trees on CM and CT accumulated the lowest soluble 1997, 1999, 2000a, 2000b). Findings from these studies have solids, while fruit from trees on SC had the highest acid con- revealed different results and inconsistent conclusions, which tent and fruit from trees on VL and CT had the lowest acid con- were attributed to several factors including climatic conditions tent. Overall, trees on vigorous rootstocks (RL, VL, CM) and soil characteristics. Therefore, it is unwise to adopt root- performed better and were more productive than trees on other rootstocks. Trees on SC and Cleo performed the poorest. stock recommendations from one part of the world to another without a thorough evaluation locally. Since environmental conditions and cultural practices are unique and vary consid- Citrus acreage in the Kingdom of Saudi Arabia is over erably from one area to another, a long term study was carried 15,000 ha. The Najran area, located in southwest Saudi Ara- out to determine the horticultural adaptability and performance of ‘Olinda Valencia’ [C. sinensis (L.) Osbeck] orange trees on nine commercial rootstocks grown on a typical soil Florida Agricultural Experiment Station Journal Series No. N-02226. 1Corresponding author. where the Saudi Arabian citrus industry is flourishing. On-site

Proc. Fla. State Hort. Soc. 115: 2002. 17

field evaluation of rootstocks benefits local growers in select- The experiment was a complete randomized block design ing the most suitable rootstocks for their citrus cultivars under and consisted of nine treatments (rootstocks) with four replica- their specific climatic and edaphic conditions. tions of 4-tree plots. Statistical analysis was conducted using analysis of variance and Duncan’s multiple range test was used Materials and Methods for mean comparison when the F-test was significant at P < 0.05.

The experiment was conducted in Najran, Saudi Arabia, Results and Discussion to compare the effects of sour orange (Citrus aurantium L.) (SO), ‘Carrizo’ citrange [(Citrus sinensis (L.) Osbeck × Poncir- Fruit yield. Over the 7-year production period, trees on us trifoliata (L.) Raf.] (CC), ‘Cleopatra’ mandarin (Citrus resh- rough lemon (RL), ‘Volkamer’ lemon (VL), and Citrus macro- ni Hort. ex Tan.) (Cleo), rough lemon (Citrus limon) (RL), phylla (CM) were the most productive. Trees on ‘Swingle’ cit- ‘Swingle’ citrumelo [(Citrus paradisi (L.) × Poncirus trifoliata rumelo (SC) and ‘Cleopatra’ mandarin (Cleo) were the least (L.) Raf.] (SC), Taiwanica (Citrus Taiwanica) (CT), Amblycar- productive. Trees on sour orange (SO), ‘Carrizo’ citrange pa (Citrus limonellus var. Amblycarpa Hassk) (Amb), ‘Volkam- (CC), Citrus Taiwanica (CT), and Amblycarpa (Amb) were in- er’ lemon (Citrus volkameriana Ten and Pasq.) (VL), and termediate in fruit production (Table 1). The poor crop for Macrophylla (Alemow) (Citrus macrophylla Wester) (CM) on trees on Cleo was partly attributed to Phytophthora infestation, fruit yield, fruit size, individual fruit weight, peel thickness, which also reduced growth and tree size. Trees on Cleo grew and percent juice, soluble solids, and acid of ‘Olinda Valen- slowly and fruited poorly during the first few years. Trees on SC cia’ orange trees. The budwood source and budded trees were had dieback, were relatively small, and consistently produced free of virus and viroids. The trees were planted in 1987 with fewer fruit. This was consistent with Gardner and Horanic a 6.0 m by 6.0 m spacing and a tree density of 278 trees/ha. (1961) who concluded that scions on Cleo were not preco- The soil texture was loamy sand (85% sand, 11% silt, and cious. Similar results of yield problems for trees on Cleo have

4% clay) throughout the root zone having a 2.9% CaCO3 con- been found from many citrus areas in the world. Cleo is consid- tent and a pH of 8.2. The trees were managed according to ered a “lazy” rootstock because trees grafted to it fruit relatively standard local commercial practices, pruned annually, and poorly until they are 10 to 15 yrs of age (Castle et al., 1993). watered as needed using a drip irrigation system delivering The yield results of this study were consistent with results of 120 to 180 L/d. The irrigation water had a pH of 8.0 and an several studies conducted in different citrus growing regions electrical conductivity of 1.02 dS/m. In early November, each where cumulative yields were higher on trees budded on VL tree was fertilized with 1.0 kg of 18-7.9-4.2-1.5 (N-P-K-Mg) and and RL than on those budded on SC and Cleo (Castle et al., 25 kg of composted manure. One kg of N from urea was also 1988; Fallahi et al., 1989; Monteverde et al., 1988; Wutscher applied 3 times (½ in January, ¼ in March, and ¼ in May). In and Shull, 1973; Zekri, 2000b). However in other studies, no the spring, foliar sprays of manganese and zinc were also ap- significant differences in cumulative yields were found among plied. The soil was kept free of weeds using post-emergence rootstocks including Cleo, SO, CC, VL, RL, CT, and CM (Falla- herbicides. Pest populations were kept under control follow- hi et al., 1991; Hearn, 1989). Furthermore, trees on SC pro- ing a recommended pest management program. duced the most fruit yield as compared with other rootstocks Fruit yield of each tree was taken at harvest. Fruit samples (Rouse and Maxwell, 1979; Wheaton et al., 1991; Wutscher et from each experimental plot were collected for fruit quality al., 1975; Wutscher and Shull, 1976a, 1976b). All these results measurements and evaluations. Individual fruit weight, fruit di- indicated the inconsistency in yield differences as affected by ameter, peel thickness, juice weight, total soluble solids or Brix, rootstocks, which could be attributed to differences in scion and titratable acid concentrations were determined in the labo- cultivars, tree age, climatic conditions, and soil characteristics. ratory using standard procedures. Juice was extracted from the Fruit size. The greatest individual fruit weight and largest fruit samples, weighed, and tested for Brix and acid. The Brix fruit were found from trees on VL and CM, while the lightest content (mostly soluble sugars) was determined using a hy- weight per fruit and smallest fruit were found on trees bud- drometer that measured the specific gravity, which was convert- ded on Cleo and SO (Tables 2 and 3). Similar results were ed to degrees Brix. The percent acid was determined by titration found by several other workers where fruit were smaller and using sodium hydroxide and a phenolphthalein indicator. lighter from trees on SO and Cleo and/or larger and heavier

Table l. Fruit yield (kg/tree) of ‘Olinda Valencia’ trees on nine rootstocks.

Rootstock

Year SO CC Cleo RL SC CT Amb VL CM 1993 62.25z 91.50 59.50 104.25 41.25 73.50 66.75 128.00 137.25 1994 85.75 101.00 75.75 119.25 60.00 99.50 89.50 128.25 128.00 1995 151.88 121.88 123.75 126.25 82.50 123.75 151.75 144.38 151.88 1996 85.00 80.00 84.38 87.19 62.81 83.44 88.75 82.50 68.44 1997 101.20 97.20 106.95 89.33 100.63 97.08 90.65 94.63 111.40 1998 98.25 92.88 82.88 84.00 41.13 102.13 84.38 85.75 57.88 1999 83.80 74.58 84.00 113.85 72.33 78.25 111.75 90.25 102.88 Averagey 95.45 abx 91.15 ab 88.17 b 103.45 ab 65.81 c 93.95 ab 97.65 ab 107.68 a 108.25 a zMean of four replications. yMean of twenty-eight measurements (four replications by seven years). xSuperscripts indicate mean separation within the last row (among rootstocks) by Duncan’s multiple range test, 0.05 level.

18 Proc. Fla. State Hort. Soc. 115: 2002.

Table 2. Individual fruit weight (g) of ‘Olinda Valencia’ trees on nine rootstocks.

Rootstock

Year SO CC Cleo RL SC CT Amb VL CM 1993 222.60z 233.15 195.60 211.53 210.05 243.25 227.53 212.08 274.03 1994 222.03 229.30 197.53 242.75 210.98 223.58 221.95 269.83 241.93 1995 197.83 245.75 201.90 226.75 217.15 240.05 226.95 242.98 252.03 1997 210.73 240.3 188.60 235.93 238.23 219.03 225.68 220.35 220.93 1998 189.53 176.03 181.48 213.38 170.18 201.48 195.58 254.20 231.25 1999 199.05 193.65 165.30 222.73 221.00 228.20 230.35 232.48 218.65 Averagey 206.93 cx 219.70 bc 188.40 d 225.51 ab 211.26 bc 225.93 ab 221.34 bc 238.65 a 239.80 a zMean of four replications. yMean of twenty-four measurements (four replications by six years). xSuperscripts indicate mean separation within the last row (among rootstocks) by Duncan’s multiple range test, 0.05 level. from trees on VL and RL (Continella et al., 1988; Economides gelo was higher for trees on RL (Fallahi et al., 1991) and that and Gregoriou, 1993; Monteverde et al., 1988; Rouse and of grapefruit was higher on CT (Fallahi et al., 1989) as com- Maxwell, 1979; Wutscher and Shull, 1976a; Zekri, 2000b). On pared with CC. Fruit rind thickness was found to be the high- the other hand, no significant differences were found in ‘Va- est for ‘Marsh’ grapefruit trees on CT and Amb and the lowest lencia’ orange fruit size and weight among trees growing on for trees on SC, CC, and ‘Estes’ RL (Economides and Grego- RL, Cleo, SO, and CT (Wutscher and Shull, 1973) and ‘Fair- riou, 1993). Trees on SO and VL produced fruit with the child’ fruit weight was higher from trees on CT than fruit thickest rind (Monteverde et al., 1988; Wutscher and Bistline, from trees on RL, CC, and CM (Fallahi and Rodney, 1992). 1988). However for ‘Marrs’ oranges, rind thickness was the Furthermore, ‘Ambersweet’ orange fruit from trees on Cleo highest from trees on SC (Wutscher and Shull, 1976b) and were found larger and heavier than those from trees on SC, grapefruit rind thickness was higher for fruit from trees on which could be attributed to the low number of fruit per tree Cleo than CT and RL (Wutscher et al., 1975). From all those on Cleo (Zekri, 1996). In general, fruit size is correlated with studies, there is no consistent trend that the more vigorous fruit number per tree. The fewer the fruit on the tree, the rootstocks promoted thicker peel. Furthermore, not all root- larger and heavier are the fruit. Moreover, in a particular year stock studies showed differences in peel or rind thickness beside fruit load, the ultimate size a citrus fruit achieves is the among rootstocks. Wutscher and Shull (1976a) did not find a result of many complex factors including nutrition and irriga- significant difference in rind thickness of ‘Orlando tangelo tion programs, rainfall distribution, pruning, and the root- fruit from trees grown on all the 4 rootstocks studied, SC, SO, stock-scion combination. Large fruit size is most often Cleo, and CT. preferred in the fresh fruit market and brings higher prices Juice content. Overall, juice content by being over 50%, was early in the season. relatively good. The juicier the fruit, the better is its accep- Peel thickness. Another determinant of citrus fresh quality tance not only for the juice market but also as a fresh fruit. is peel thickness, firmness or texture. Both extremes in peel Like other fruit quality variables, juice content was affected by thickness are not desirable. Fruit with thick peel are usually the rootstock and varied through the years. Fruit from trees low in juice, while those with thin peel are prone to splitting on SC had the highest juice content while those from trees on and are sensitive to postharvest problems that can occur dur- SO, RL, and CT had the lowest juice content (Table 5). Simi- ing shipping and storage. Peel thickness was also affected by lar results were reported from some earlier studies. Fruit from the rootstock. Peel thickness was the highest in fruit collected trees on SC and Cleo had the best juice percentage compared from trees on CT and CM and the lowest in fruit collected with trees on VL, CC, and SO (Monteverde et al., 1988). Fruit from those on Cleo, SC, and Amb (Table 4). Differences in from trees on CT had the lowest percent juice compared with fruit peel thickness as affected by rootstocks were also report- RL, VL, RL, CM, and CC (Fallahi et al., 1989). Fruit from trees ed in some previous studies. Peel thickness of ‘Orlando’ tan- on CC and RL contained more juice than those from trees on

Table 3. Fruit diameter (cm) of ‘Olinda Valencia’ trees on nine rootstocks.

Rootstock

Year SO CC Cleo RL SC CT Amb VL CM 1993 7.23z 7.48 7.08 7.25 6.88 7.65 7.43 7.30 7.80 1994 7.35 7.28 7.08 7.58 7.18 7.38 7.38 7.93 7.58 1995 7.05 7.58 7.18 7.45 7.38 7.58 7.40 7.63 7.70 1997 7.08 7.38 6.75 7.45 7.35 7.23 7.20 7.30 7.20 1998 7.03 6.88 7.03 7.35 6.95 7.30 6.95 7.50 7.70 1999 7.20 6.85 6.73 7.20 7.55 7.50 7.60 7.08 7.40 Averagey 7.15 dx 7.24 cd 6.98 e 7.38 bc 7.21 cd 7.44 ab 7.33 bcd 7.45 ab 7.56 a zMean of four replications. yMean of twenty-four measurements (four replications by six years). xSuperscripts indicate mean separation within the last row (among rootstocks) by Duncan’s multiple range test, 0.05 level.

Proc. Fla. State Hort. Soc. 115: 2002. 19

Table 4. Peel thickness (mm) of fruit from ‘Olinda Valencia’ trees on nine rootstocks.

Rootstock

Year SO CC Cleo RL SC CT Amb VL CM 1993 5.28z 5.53 4.95 5.25 4.78 5.68 5.30 5.13 5.63 1994 4.98 4.90 4.70 5.03 5.04 4.90 4.60 5.25 5.15 1995 3.75 4.70 4.10 4.48 4.03 4.35 3.95 3.85 4.23 1997 4.68 4.48 4.53 4.78 4.38 4.50 4.45 4.55 4.60 1998 5.05 4.88 5.28 5.15 5.13 5.78 5.23 5.33 5.60 1999 5.48 5.05 4.65 5.23 4.73 5.65 4.83 4.93 5.78 Averagey 4.87 abx 4.92 ab 4.70 b 4.98 ab 4.68 b 5.14 a 4.73 b 4.84 ab 5.16 a zMean of four replications. yMean of twenty-four measurements (four replications by six years). xSuperscripts indicate mean separation within the last row (among rootstocks) by Duncan’s multiple range test, 0.05 level.

CM (Fallahi et al., 1991). However, juice content of ‘Marrs’ were among the highest from fruit on SO (Monteverde et al., orange was the highest for trees on SO and the lowest for 1988; Wutscher and Shull, 1973; Wutscher and Shull, 1976b). trees on CT (Wutscher and Shull, 1976b). In general, the Fruit from trees on SO, CC and/or Cleo had the highest sol- larger the fruit and the thicker the peel or rind, the lower is uble solids concentration, while those on VL and RL had the the juice content. Juice content was the highest for SO and lowest soluble solids concentration (Castle et al., 1988; Conti- the lowest for ‘Estes’ RL, VL, Amb and Cleo (Economides and nella et al., 1988; Fallahi et al., 1989; Fallahi and Rodney, Gregoriou, 1993), and ‘Hamlin’ fruit from trees on RL and 1992; Wutscher and Bistline, 1988). Total soluble solids were VL had the lowest percent juice (Wutscher and Bistline, among the highest for fruit from trees on SC and the lowest 1988). On the other hand, not all rootstock studies demon- for fruit from trees on RL, VL and Milam (Economides and strated that rootstocks had an influence on juice content. For Gregoriou, 1993; Zekri, 2000b). The results on soluble solids example, no significant difference in juice content of ‘Orlan- for all these studies are consistent, showing poorer internal do’ tangelo, ‘Comune’ Clementine, ‘Fairchild’ mandarin and fruit quality for trees grown on relatively vigorous rootstocks grapefruit was found from trees grown on all the studied root- such as RL and VL, compared with trees grown on less vigor- stocks (Wutscher and Shull, 1976a; Continella et al., 1988; ous rootstocks such SC and SO. Fallahi and Rodney, 1992; Wutscher et al., 1975). Acid content. Total acidity of citrus juices is an important Soluble solids. The flavor and palatability of citrus fruits is a factor in overall juice quality and in determining time of har- function of relative levels of soluble solids, acids, and pres- vest in several citrus producing countries. Acid content in the ence or absence of various aromatic or bitter juice constitu- juice was found to be affected by rootstocks. Acid content in ents. Although fruit quality standards, which determine the juice of fruit from trees on SC and Amb was higher than minimum levels of acceptability, have not been established in that from trees on SO, Cleo, RL, CT, and VL (Table 7). Simi- Saudi Arabia, soluble solids concentration in the juice has not lar results were found by other workers. The lowest total acids been completely ignored as an important parameter for fresh in the fruit juice were from trees on CT and the highest were fruit. Rootstocks were found to affect soluble solids concen- from trees on SC (Wutscher and Shull, 1976a, 1976b). Acid tration in fruit juice. Soluble solids concentration in fruit content was the highest for trees grown on SO and the lowest from trees on SO and CC was the highest, while it was the low- for trees on VL and RL (Continella, 1988). Total acid was est for fruit from those on RL, CT, VL, and CM (Table 6). among the highest in the juice from trees on CC, SC and Cleo Other workers have found similar results. Total soluble solids and the lowest from trees on RL and VL (Fallahi et al., 1989, were the lowest for RL and the highest for Cleo and SO 1991; Wutscher and Bistline, 1988; Wutscher et al., 1975). (Hearn, 1989; Wutscher et al., 1975). Total soluble solids However, no significant difference in juice content was found

Table 5. Juice content (% wt) of fruit from ‘Olinda Valencia’ trees on nine rootstocks.

Rootstock

Year SO CC Cleo RL SC CT Amb VL CM 1993 50.63z 52.38 52.05 49.90 53.35 50.43 51.90 52.80 51.30 1994 53.08 55.43 56.00 55.95 55.08 55.80 55.93 54.90 54.85 1995 55.68 55.58 56.35 54.05 58.58 55.20 56.60 56.28 55.94 1997 49.18 51.55 49.30 47.03 53.05 48.48 49.63 50.13 50.73 1998 50.55 47.58 51.30 50.93 52.03 50.20 50.80 51.85 50.53 1999 49.08 52.48 48.68 48.83 50.15 48.30 51.43 50.68 47.75 Averagey 51.36 bx 52.50 ab 52.28 ab 51.11 b 53.70 a 51.40 b 52.71 ab 52.77 ab 51.85 ab zMean of four replications. yMean of twenty-four measurements (four replications by six years). xSuperscripts indicate mean separation within the last row (among rootstocks) by Duncan’s multiple range test, 0.05 level.

20 Proc. Fla. State Hort. Soc. 115: 2002.

Table 6. Soluble solids concentration (%) of fruit from ‘Olinda Valencia’ trees on nine rootstocks.

Rootstock

Year SO CC Cleo RL SC CT Amb VL CM

1993 12.35z 12.93 12.70 12.33 13.63 11.58 12.68 12.65 10.93 1994 13.38 13.90 12.98 12.15 12.65 12.10 13.15 11.75 12.48 1995 13.63 12.93 12.65 11.78 12.33 11.50 13.40 12.10 11.15 1997 13.45 13.00 13.45 11.45 12.30 11.68 12.30 12.50 11.63 1998 14.33 15.38 14.25 13.03 13.30 12.48 13.98 12.43 12.25 1999 13.73 13.93 13.78 12.23 12.05 11.23 12.60 12.33 12.40 Averagey 13.48 ax 13.68 a 13.30 ab 12.16 ef 12.71 cd 11.76 f 13.02 bc 12.29 de 11.80 f

zMean of four replications. yMean of twenty-four measurements (four replications by six years). xSuperscripts indicate mean separation within the last row (among rootstocks) by Duncan’s multiple range test, 0.05 level.

Table 7. Acid content (%) of fruit from ‘Olinda Valencia’ trees on nine rootstocks.

Rootstock

Year SO CC Cleo RL SC CT Amb VL CM 1993 0.78z 0.84 0.87 0.81 0.97 0.80 0.87 0.86 0.85 1994 0.91 0.90 0.76 0.86 1.16 0.81 0.86 0.82 0.84 1995 0.86 0.88 0.87 0.83 1.19 0.85 1.06 0.84 0.90 1997 0.97 1.02 0.98 0.97 1.20 0.87 1.14 0.92 1.03 1998 0.84 0.93 0.98 0.82 1.15 0.81 0.95 0.86 0.86 1999 1.08 1.10 1.09 1.16 1.19 1.12 1.16 1.06 1.20 Averagey 0.91 cx 0.94 bc 0.91 c 0.91 c 1.14 a 0.88 c 1.00 b 0.89 c 0.95 bc

among trees grown on VL, CC, CT, RL, and CM (Fallahi and Literature Cited Rodney, 1992). Although internal fruit quality including acid content can be affected by the scion cultivar, tree age and oth- Castle, W. S., D. P. H. Tucker, A. H. Krezdorn, and C. O. Youtsey. 1993. Root- er factors, the results on acid content from most of these stud- stocks for Florida citrus. Fla. Coop. Ext. Serv. Bull. SP 42. ies are consistent showing relatively lower acid content for Castle, W. S., H. K. Wutscher, C. O. Youtsey, and R. R. Pelosi. 1988. Citrume- trees grown on lemon rootstocks. los as rootstocks for Florida citrus. Proc. Fla. State Hort. Soc. 101:28-33. Continella, G., C. Germana, G. La Rosa, and E. Tribulato. 1988. Performance and physiological parameters of ‘Comune’ Clementine influenced by four rootstocks. Proc. Sixth Intern. Citrus Congr. p. 91-100. Conclusions Economides, C. V. and C. Gregoriou. 1993. Growth, yield, and fruit quality of nucellar frost ‘Marsh’ grapefruit on fifteen rootstocks in Cyprus. J. Amer. Rootstocks can affect the success and profitability of vir- Soc. Hort. Sci. 118:326-329. tually any commercial citrus culture. Rootstock use is consid- Fallahi, E., J. W. Moon, Jr., and D. R. Rodney. 1989. Yield and quality of ‘Red- blush’ grapefruit on twelve rootstocks. J. Amer. Soc. Hort. Sci., 114:187- ered essential in citriculture because of its strong influence 190. on how and where citrus can be grown successfully. In this Fallahi, E., Z. Mousavi, and D. R. Rodney. 1991. Performance of ‘Orlando’ study, it was quite obvious that rootstocks had a significant ef- trees on ten rootstocks in Arizona. J. Amer. Soc. Hort. Sci. 116:2-5. fect of fruit yield and quality. Failure to assess accurately the Fallahi, E. and D. R. Rodney. 1992. Tree size, yield, fruit quality, and leaf mineral nutrient concentration of ‘Fairchild’ mandarin on six rootstocks. J. impact of climate, soils, and rootstocks on economic profit- Amer. Soc. Hort. Sci. 117:28-31. ability of citrus can be a major reason for crop losses or re- Gardner, F. E. and G. E. Horanic. 1961. A comparative evaluation of root- duced income because of reduced yield and quality stocks for Valencia and Parson Brown oranges on Lakeland fine sand. potential. Trees on CM, VL, and RL rootstocks were more Proc. Fla. State Hort. Soc. 74:123-127. vigorous, precocious and more productive than those on the Gardner, F. E. and G. E. Horanic. 1966. Growth, yield, and fruit quality of Marsh grapefruit on various rootstocks on the Florida East Coast - A pre- other rootstocks. Cleo and SC rootstocks are not recom- liminary report. Proc. Fla. State Hort. Soc. 79:109-114. mended for the Najran area of Saudi Arabia because of Grisoni, M., P. Cabeu, and B. Aubert. 1989. Resultats de douze annees d’ un Cleo’s high susceptibility to Phytophthora particularly in essai de comportement de cinq porte-greffe en association avec quatre poorly drained situations and because of SC poor adaptabil- cultivars d’agrumes a l’ile de la Reunion. Fruits 44:529-537. Hearn, C. J. 1989. Yield and fruit quality of ‘Ambersweet’ orange hybrid on ity to high pH soil, calcareous soils, and/or relatively saline different rootstocks. Proc. Fla. State Hort. Soc. 102:75-78. environment. Based on this study, CM, VL, and RL are good Monteverde, E. E., F. J. Reyes, G. Laborem, and J. R. Ruiz. 1988. Citrus root- choices as rootstocks for ‘Valencia’ orange in the Najran area stocks in Venezuela: Behavior of Valencia orange on ten rootstocks. Proc. of Saudi Arabia. Sixth Inter. Citrus Congr. 47-55.

Proc. Fla. State Hort. Soc. 115: 2002. 21

Roose, M. L., D. A. Cole, D. Atkin, and R. S. Kupper. 1989. Yield and tree size Wutscher, H. K. and A. V. Shull. 1976a. Performance of ‘Orlando’ tangelo on of four citrus cultivars on 21 rootstocks in California. J. Amer. Soc. Hort. 16 rootstocks. J. Amer. Soc. Hort. Sci. 101:88-91. Sci. 114:678- 684. Wutscher, H. K. and A. V. Shull. 1976b. Performance of ‘Marrs’ early orange Rouse, R. E. and N. P. Maxwell. 1979. Performance of mature nucellar ‘Red- on eleven rootstocks in south Texas. J. Amer. Soc. Hort. Sci. 101:158-161. blush’ grapefruit on 22 rootstocks in Texas. J. Amer. Soc. Hort. Sci. Zekri, M. 1996. Leaf mineral concentration, growth, yield, fruit quality, and 104:449-451. economics of ‘Ambersweet’ orange trees on two rootstocks. Proc. Fla. Wheaton, T. A., W. S. Castle, J. D. Whitney, and D. P. H. Tucker. 1991. Per- State Hort. Soc. 109:92-96. formance of citrus scion cultivars and rootstocks in a high-density plant- Zekri, M. 1997. Performance of Ambersweet, a new citrus hybrid cultivar, on ing. HortScience 26:837-840. two rootstocks in Florida. Fruits 52:141-148. Wutscher, H. K. and F. W. Bistline. 1988. Performance of ‘Hamlin’ orange on Zekri, M. 1999. Performance of ‘Valencia’ orange trees on four rootstocks in 30 citrus rootstocks in southern Florida. J. Amer. Soc. Hort. Sci. 113:493- a high-density planting. Proc. Interamer. Soc. for Trop. Hort. 43:108-115. 497. Zekri, M. 2000a. Citrus rootstocks affect scion nutrition, fruit quality, growth, Wutscher, H. K., N. P. Maxwell, and A. V. Shull. 1975. Performance of nucel- yield and economical return. Fruits 55:231-239. lar grapefruit, Citrus paradisi Macf., on 13 rootstocks in south Texas. J. Am- Zekri, M. 2000b. Evaluation of orange trees budded on several rootstocks and er. Soc. Hort. Sci. 100:48-51. planted at high density on flatwoods soil. Proc. Fla. State Hort. Soc. Wutscher, H. K. and A. V. Shull. 1973. The performance of Valencia orange 113:119-123. trees on 16 rootstocks in south Texas. Proc. Trop. Reg. Amer. Soc. Hort. Zekri, M. and A. Al-Jaleel. 2000. The citrus industry in Saudi Arabia. The Cit- Sci. 17:66-73. rus Industry Mag. 81:24-26.

Proc. Fla. State Hort. Soc. 115:22-26. 2002. PRUNING AND SKIRTING EFFECTS ON CANOPY MICROCLIMATE, GROWTH, AND FLOWERING OF ‘ORLANDO’ TANGELO TREES

PAULA MORALES AND FREDERICK S. DAVIES1 skirted, non-pruned trees than for other treatments. The fol- University of Florida lowing season, shoot number was the lowest in gable-topped Horticultural Sciences Department trees. Flowering the following season was not affected by Gainesville, FL 32611 pruning or skirting treatments. The upper canopy had more leafy and leafless inflorescences than the sides of the tree for all treatments. Additional index words. citrus, temperature, relative humidity The vegetative response of citrus to pruning depends on Abstract. Pruning and skirting effects on canopy temperature the date and intensity of pruning. Pruning vigorous oranges and relative humidity (RH), vegetative growth and flowering of trees in fall or winter resulted in less vigorous (Moss, 1973) ‘Orlando’ tangelo trees [Citrus paradisi Macf. × Citrus reticula- ta Blanco] on Carrizo citrange rootstock [C. sinensis (L.) Osb. and less fruitful (Bacon, 1981) regrowth than trees pruned in × Poncirus trifoliata (L.) Raf.] were studied at the University of spring. Little difference in the vegetative response was found Florida Fifield Farm in Gainesville, Fla. during 1997-98. Two if ‘Valencia’ orange trees were hedged between spring and skirting (skirted or non-skirted) and three pruning (gable-top, early summer (Bacon, 1981). Moore and Nauer (1955) sug- flat-top or non- pruned) treatments were evaluated. Trees were gested that adequate regrowth was obtained by pruning from skirted and pruned in Mar. 1997. Vegetative regrowth and flow- late winter to late summer. Bevington and Bacon (1978) ering were measured using frame counts and shoot length was found that it was preferable to prune after fruit set in order to measured at the end of each growth flush in 1997 and 1998. have an idea of the next year’s crop before hedging. Bacon Large diurnal fluctuations in RH were observed throughout the (1981) reported that hedging time did not increase final season in all treatments. The RH in the bottom-inside canopy flush length since the first flush that comes after hedging decreased to about 50% during the day and increased to 100% at night. Diurnal fluctuations in RH were greater in the upper reaches a certain length independent of hedging time or time than lower canopy. RH in the bottom of skirted trees was sim- interval between hedging and regrowth. However, Fucik ilar to that of non-skirted trees and was also similar for all prun- (1978) reported that large branches pruned in March pro- ing treatments. Skirting and pruning did not affect air duced the longest shoots in July. The length of the second temperature in the bottom canopy. In contrast, temperature in and third flushes following pruning was greater for branches the upper canopy of flat-topped trees was 18°F higher than that pruned from spring to early summer than for branches of gable-topped and non-pruned trees and reached more than pruned in fall (Bevington and Bacon, 1978). 114°F during spring and summer. Shoot number and length Pruning influences flowering by increasing the number of were the same for all treatments during the season of pruning, new shoots and thus potential flowering sites (Krajewski and but total length was higher for skirted, gable topped and non- Rabel, 1995a). However, Bevington and Bacon (1976) and Wheaton et al. (1984) suggest that the first growth flushes This research was supported by the Florida Agricultural Experiment Sta- produced after severe pruning usually do not flower. Similar- tion, and approved for publication as Journal Series No. N-02228. ly, ‘Valencia’ orange trees did not flower or fruit during the 1Corresponding author.

22 Proc. Fla. State Hort. Soc. 115: 2002.