good tolerance to blight and high pH soils. Small scale exotic isolates of citrus tristeza virus. Proc. Fla. State Hort. Soc. 105: commercial trials with each rootstock are justified. (In press). Garnsey, S. M., R. F. Lee, C. O. Youtsey, R. H. Brlansky, and H. C. Burnett. 1980. A survey for citrus tristeza virus in registered budwood Literature Cited sources commercially propagated on sour orange rootstocks in Florida. Proc. Fla. State Hort. Soc. 93:7-9. Barrett, H. C. and A. M. Rhodes. 1976. A numerical taxonomic study of Grimm, G. R. and S. M. Garnsey. 1968. Foot rot and tristeza tolerance affinity relationships in cultivated Citrus and its close relatives. System. of Smooth Seville orange from two sources. Proc. Fla. State Hort. Soc. Bot. 1(2): 105-136. 81:84-90. Bevington, K. B. and B. R. Cullis. 1990. Evaluation of rootstocks for Hodgson, R. W. 1967. Horticultural varieties of citrus, p. 431-591. In: Marsh and Davis grapefruit in the Murray Region of New South W. Reuther, H. J. Webber, and L. D. Batchelor (eds.). The citrus Wales. Aust. J. Expt. Agr. 30:405-411. industry, vol. 1. University of California Press, Berkeley. Broadbent, P. and B. I. Gollnow. 1992. Selecting disease-tolerant citrus Hutchison, D. J. and F. W. Bistline. 1981. Preliminary performance of rootstocks for Australia. Proc. Intern. Soc. Citriculture (in press). 7-yr-old 'Valencia' orange trees on 21 rootstocks. Proc. Fla. State Hort. Castle, W. S. 1987. Citrus rootstocks. p. 361-399. In: R. C. Rom and R. Soc. 94:31-33. F. Carlson (eds.). Rootstocks for fruit crops. J. Wiley and Sons, NY. Permar, T. A., S. M. Garnsey, D. J. Gumpf, and R. F. Lee. 1990. A Chao, H-Y., Y-H. Chiang, C-B. Chang, C-S. Chiu, and W-F. Su. 1979. monoclonal antibody that discriminates strains of citrus tristeza virus. Distribution of seedling yellows tristeza virus in citrus and the tristeza Phytopathology 80:224-228. susceptibility of six sour orange rootstocks. Acta Phytopath. Sinica Van Vuuren, S. P., N. M. Greech, and R. P. Collins. 1991. Reaction of 9(l):61-72. Gou Tou orange to the citrus nematode, Phytophthora and citrus Derrick, K. S., G. A. Barthe, B. G. Hewitt, and R. F. Lee. 1990. A spot tristeza virus, p. 128-134. In: R. H. Brlansky, R. F. Lee and L. W. test for citrus blight. Citrus Ind. 71(2):56, 57. Timmer (eds.). Proc. 1 lth Conf. Intern. Org. Citrus Virol., Riverside, Gardner, F. E. and G. E. Horanic. 1966. Growth, yield and fruit quality CA. of Marsh grapefruit on various rootstocks on the Florida east coast—a Wutscher, H. K. 1977. The influence of rootstocks on yield and quality preliminary report. Proc. Fla. State Hort. Soc. 79:109-114. of red grapefruit in Texas. Proc. Intern. Soc. Citriculture 2:526-529. Gardner, F. E., D. J. Hutchison, G. E. Horanic, and P. C. Hutchins. 1967. Youtsey, C. O. and L. H. Hebb. 1982. Tristeza decline in four grapefruit Growth and productivity of virus-infected Valencia orange trees on cultivars at the budwood foundation grove, Dundee, Florida. Proc. twenty-five rootstocks. Proc. Fla. State Hort. Soc. 80:89-92. Fla. State Hort. Soc. 95:60-63. Garnsey, S. M. 1990. Seedling yellows isolates of citrus tristeza virus in Youtsey, C. O. and F. J. Rosenthal. 1986. Incidence of citrus blight in commercial citrus in Florida. Proc. Fla. State Hort. Soc. 103:83-87. Florida's citrus budwood foundation grove. Proc. Fla. State Hort. Soc. Garnsey, S. M. 1992. Tolerance of Gou Tou orange rootstocks to severe 99:71-73. Proc. Fla. State Hort. Soc. 105:60-63. 1992. THE PERFORMANCE OF 'VALENCIA' ORANGE TREES ON 21 ROOTSTOCKS IN THE FLORIDA FLATWOODS D. J. Hutchison and C. J. Hearn sour orange No. 2 (C aurantium), and Yuma. The largest U.S. Department of Agriculture trees were on sour orange No. 2, Yuma, and Sun Chu Sha. Agricultural Research Service U.S. Horticultural Research Laboratory Valencia' orange, Citrus sinensis (L.) Osbeck, is the 2120 Camden Road, Orlando, FL 32803 major citrus cultivar grown throughout the world. It is grown extensively in Florida in the deep, sandy soils of the F. W. Bistline central Ridge and the shallow soils of the flatwoods. The Coca-Cola, Inc., Foods Division Florida flatwoods soils are shallow over hardpans or lime P.O. Box 247, Auburndale, FL 33823 stone and range from acid to alkaline, poorly drained and highly variable. Extensive preplant site preparation is Additional index words, tree size, yield, fruit quality, survival. necessary, including the formation of beds to give the trees rooting space, the dredging of drainage ditches, and instal Abstract. 'Valencia' orange, Citrus sinensis (L.) Osbeck, was lation of irrigation systems because the shallow root sys grown on 21 rootstocks for 15 years in an area near Fort tems make the trees drought prone (Wutscher and Pierce, Florida. There were four 8-tree replications in ran Bistline, 1988). The rootstock-related diseases of citrus domized blocks, with 4.6 X 8.2 m spacing. Yield was deter blight (Smith and Reitz, 1977), citrus tristeza virus, and mined at 11 harvests, fruit quality at four harvests, and tree Phytophthora parasitica Dastur foot rot accentuate the pro size (canopy volume) and surviving healthy trees were re duction problems in the Florida flatwoods soils. Therefore, corded. Trees on Sun Chu Sha (C. reticulata Blanco), Yuma rootstock selection is a prime concern for ensuring the [Poncirus trifoliata (L.) Raf. hybrid], Argentina trifoliate profitability of newly established citrus plantings in the orange (P. trifoliata), and Smooth Flat Seville (C. aurantium flatwoods areas of southern Florida (Hutchison and L. hybrid) had the highest percentages of surviving healthy Bistline, 1981; Wutscher and Bistline, 1988). This report trees. Cumulative yield (kg/tree and kg solids/tree) was high presents information on the performance of a wide range est on Sun Chu Sha, Volkamer lemon [ C. limon (L.) Burm. f.], of rootstocks grown in the flatwoods of southern Florida. Materials and Methods Mention of a trademark, warranty, proprietary product, or vendor does not constitute a guarantee by the U.S. Department of Agriculture The planting site was near Ft. Pierce, Fla., where the and does not imply its approval to the exclusion of other products or soil was a shallow, poorly drained, fine loamy, depres- vendors that may also be suitable. 60 Proc. Fla. State Hort. Soc. 105: 1992. sional, siliceous (Winder sand, depressional type) ponded centages were determined on 20-fruit samples from each throughout most of the year, and has a variable pH level plot and the 4-year averages (1981, 1985, 1986, and 1989) (5.6-7.0). Land preparation, prior to planting citrus, con calculated. The juice was extracted by hand with a motor- sisted of dredging drainage ditches, formation of raised driven reamer. TSS was determined with a temperature- planting beds, and installation of an irrigation system. compensated refractometer, and TA by titration of 10 ml Trees on rough lemon [C. limon (L.) Burm. f.] rootstock of juice in 90 ml of distilled water with 0.1560 N NaOH to were originally planted at this site; however, the trees were a pH of 8.2. Tree size, expressed as canopy volume ca/cu- removed after 12 years because of extensive losses due to lated by the formula width2 X height/4 (Hutchison et al., citrus blight. Adjacent beds were planted with trees on sour 1972), was determined in 1989. Data were subjected to orange (C. aurantium L.) rootstock and extensive losses to analysis of variance and the means separated using Dun citrus tristeza virus (CTV) forced a change to rootstocks can's multiple range test. other than rough lemon and sour orange. Trees at this location also had a high incidence of Phytophthora parasitica Results and Discussion Dastur foot rot. The rootstock cultivars (Table 1) used in this experiment were selected on the basis of their broad Table 2 shows the number of trees declining and lost genetic diversity. to diseases. Several trees declined and died within 3 years Seeds of the rootstock cultivars were planted in a field after the experiment was planted due to foot rot and root seedbed in 1971 and lined out in a field nursery in 1972. rot caused by Phytophthora parasitica (Dastur). The greatest All of the rootstock cultivars produced uniform seedling losses to Phytophthora were incurred by red rough lemon populations, except Yuma, where 50% of the seedlings had 2, Chase rough lemon, and Cleopatra mandarin to be discarded due to their variability. The seedlings were rootstocks; these rootstocks have been reported as suscep budded with a nucellar 'Valencia' orange (Budwood Regis tible to P. parasitica (Carpenter, et al., 1975; Hutchison, tration Bureau, Florida Department of Plant Industry No. 1977). Subsequently, trees on Tunis sour orange, sour F/37-4) in the spring of 1973, and the trees were trans orange No. 2, Argentina sour orange, and CRC-1449, and planted to the field in February 1974 and arranged in a to a lesser extent on Yuma rootstocks (based on visual stem randomized complete block design. Plot size was 4 rows x pitting and IKI starch test), were lost or declined due to 2 trees in the row, with 4 replications and a tree spacing CTV (S. M. Garnsey, personal communication). A high of 4.6 x 8.2 m. The experimental planting was given nor incidence of citrus blight (based on visual symptoms) was mal commercial grove maintenance. Data were recorded observed on trees on Argentina trifoliate orange, Carrizo from the 4 center trees of each replication.