Freie, R. L. and R. D. Gaskalla. 1994. Commercial citrus inventory 1994. Flor Wheaton, T. A., J. D. Whitney, W. S. Castle, and D. P. H. Tucker. 1986. Tree ida Agricultural Statistics Service, 1222 Woodward St., Orlando, FL. spacing and rootstock affect growth, yield, fruit quality, and freeze dam Hutton, R.J. 1986. The influence of tree size control and plant density on cit age of young 'Hamlin' and 'Valencia' orange trees. Proc. Fla. State Hort. rus productivity. Acta Hort. 175:249-254. Soc. 99:29-32. Koo, R. C.J. and R. P. Muraro. 1982. Effect of tree spacing on fruit produc Wheaton, T. A., J. D. Whitney, D. P. H. Tucker, and W. S. Castle. 1984. Cross tion and net returns of 'Pineapple' oranges. Proc. Fla. State Hort. Soc. hedging, tree removal, and topping affect fruit yield and quality of citrus 95:29-33. hedgerows. Proc. Int. Soc. Citriculture 1:109-114. Paul, V. K. 1987. High density planting and dwarf rootstocks in citrus - a re Wheaton, T. A., J. D. Whitney, W. S. Castle, R. P. Muraro, H. W. Browning, view. J. Maharashtra Agric. Univ. 12(2):189-194. and D. P. H. Tucker. 1995. Citrus scion and rootstock, topping height, Tachibana, S., S. Morioka, and S. Nakai. 1987. Effect of planting density on and tree spacing affect tree size, yield, fruit quality, and economic return. fruit yield under different cultural treatments in Satsuma mandarin tree. J. Amer. Soc. Hort. Sci. 120:861-870. J.Japan. Soc. Hort. Sci. 56:9-15. Whitney, J. D., A. Elezaby, W. S. Castle, T. A. Wheaton, and R. C. Littell. 1991. Wheaton, T. A., W. S. Castle, D. P. H. Tucker, andj. D. Whitney. 1978. Higher Citrus tree spacing effects on soil water use, root density, and fruit yield. density plantings for Florida citrus - concepts. Proc. Fla. State Hort. Soc. Trans. Amer. Soc. Agr. Eng. 34:129-134. 91:27-33. Whitney, J. D., T. A. Wheaton, W. S. Castle, and D. P. H. Tucker. 1994. Opti Wheaton, T. A., W. S. Castle,J. D. Whitney, D. P. H. Tucker, and R. P. Muraro. mizing orange grove factors for fruit production and harvesting. Trans. 1990. A high density citrus planting. Proc. Fla. State Hort. Soc. 103:55-59. Amer. Soc. Agr. Eng. 37:365-371. Proc. Fla. State Hort. Soc. 108:69-73. 1995. "A 6-YEAR COMPARISON BETWEEN 16 ROOTSTOCKS BUDDED WITH 'HAMLIN' SWEET ORANGE' Charles O. Youtsey1 Introduction Florida Department of Agriculture & Consumer Services In 1955, Dr. Mortimer Cohen, then a pathologist with the Division of Plant Industry State Plant Board in Gainesville, made controlled pollina Bureau of Citrus Budwood Registration tions among selected trees in the University of Florida horti 3027 Lake Alfred Road, Winter Haven, Fl 33881-1438 cultural grove on Archer Road as part of his interest in horticultural characteristics of nucellar citrus seedlings. Orie Lee, Lee Associates Fruits from these pollinations were harvested in January and 5005 Lillian Lee Road March of 1956 and seed was planted. Many of these nucellar St. Cloud, Fl 34771 and zygotic seedlings were subsequently planted in 1960 at the Division of Plant Industry Budwood Foundation Grove lo Additional index words. Citrumelo, citrange. cated near U.S. 27 and 1-4 in Polk County. After extensive evaluation by personnel from the Citrus Abstract. Yields, juice quality, and tree size were recorded from Budwood Registration Office, nucellar selections of 'Pineap one Hamlin orange (C. sinensis (L.) Osbeck) clone on 10 un ple', navel, 'Valencia' and 'Redblush' grapefruit were re named citrumelo (Citrus paradisi Macf. x Poncirus trifoliata) leased as budwood for use by the Florida Industry beginning and 3 unnamed citrange (C. sinensis x P. trifoliata) rootstocks, in 1972 and have become popular scions commonly used in Sour orange {Citrus aurantium), Swingle citrumelo and Norton the Florida industry. (Bridges 1973) (Bridges & Youtsey 1974) citrange. Trees were planted in November 1986, spaced 14 x 22 (Norman 1964) (Pieringer et al. 1978). feet in 6 replications of 3 tree plots. Cumulative yields were Certain of the zygotic seedlings from Cohen's work were highest for trees on citrumelos F/80-3, F/81-18, W-2, F/80-2, and sour orange, and lowest for citrange F/81-10, citrumelo F/80-19 fruited and from 1968 through 1973, many seedling stands and F/80-7. Cumulative pounds soluble solids per acre were were established for evaluation of uniformity, vigor, germina highest for citrumelo F/80-3, F/81-18, F/80-2, F/80-8, and sour tion, and disease susceptibility. Several of the more uniform orange. They were lowest for citrange F/81-10, citrumelo F/80- and vigorous selections were identified for trial as rootstocks 19, and F/80-7. Tree size was calculated by measuring the ef in 1973 when the Budwood Foundation Grove was moved to fective height of fruiting. Citrumelo F/80-2,W-2, F/81-18, sour a new location near Dundee, Florida, and in other trials by orange, F/80-3 and F/80-6 were the largest trees. USDA and IFAS research scientists. (Wutscher et al. 1988) When Swingle was assigned an index of 100, there were trees (Youtsey and Bridges 1979). on seven rootstocks that produced fruit higher in the tree than Because of increased interest in the potential for use of ci- Swingle. Using Swingle as an index for production of pounds soluble solids per tree in seasons 1992-93 & 1993-94, only tranges and citrumelos, this study was undertaken to deter trees on F/80-2, F/81-18, sour orange, and F/80-3 rootstocks mine the performance of these controlled pollination out produced trees on Swingle. Tests for Citrus Tristeza Virus seedlings used as rootstocks for Hamlin sweet orange in com (CTV) in December 1992 on all trees on sour orange rootstock parison with standard commercial rootstocks. showed that 27.7% of these trees were identified with severe isolates of CTV. By August 1993, five trees on sour orange Materials and Methods rootstock were declining. In the fall of 1983, seeds were harvested and sown for 10 citrumelo, (C. paradisi cv. 'Duncan' grapefruit x P. trifoliata) 'Retired and 3 citrange (c.sinensis cv. 'Parson Brown' x P. trifoliata and Proc. Ha. State Hort. Soc. 108: 1995. 69 one cv. 'Pineapple' x P. trifoliata) seedling trees, and for Swin Results and Discussion gle citrumelo, Norton citrange, and Sauvage sour orange. Uniform seedlings were lined out in Nov. 1984 and budded Trees on F/80-3 (container grown) averaged 118 fruit per in July 1985. Budwood was taken from the H-1-4-1-X-E mother tree 2 years after planting. Trees on Swingle, F/80-8, F/81-12, tree maintained under screen at the DPI Citrus Budwood F/80-7 averaged 29 fruit per tree. Average fruit yield for all Foundation grove in Dundee. The budwood source was free rootstocks was 24 per tree. Trees began bearing a commercial of citrus tristeza virus (CTV) as well as psorosis, xyloporosis/ crop at 3 years of age and varied from 1/2 to 2 boxes. The cachexia, exocortis, and other detectable viroids. Subsequent trees on citrumelo F/80-3 rootstock led, or equaled, all other serological tests for citrus blight did not show the presence of stocks in annual yields and led sour orange and Swingle by blight specific markers (Derrick et al. 1990). Other visible 15.5% and 24.6%, respectively, in cumulative yields (Table 1). symptoms of citrus blight in the mother tree have not been Yields of scions on sour orange were reduced in the most re observed. Trees were planted in Nov. 1986 at St. Cloud, Flor cent 2 years due to CTV decline affecting 6 of the 18 trees. An ida, in soil consisting predominately of Myakka fine sand. nual yields of citrumelo F/81-18 were comparable with sour Tree spacing was 14 x 22 feet. The experimental design was a orange except in the 1992-1993 and 1994-1995 seasons and randomized complete block with 6 replications of 3-tree were comparable to or greater than Swingle in all seasons. Cu plots. Trees of the citrumelo F/80-3 were container-grown in mulative yields were less than 1% greater for F/81-18 vs. sour a commercial greenhouse (budded in September 1985) and orange, but 8.8% better than Swingle. Trees on citrange F/ were originally set in an adjacent trial, but later moved by tree 81-10, citrumelo F/80-19, and citrumelo F/80-7 yielded spade into this planting in November. 47.3%, 33.2%, and 22.2% less fruit, respectively, than Swingle For the first crop in the 1987-1988 season, fruit were for the 6-year period. Sour orange had better yields than counted from individual trees; thereafter yields were deter Swingle in most years, but CTV will cause a reduction in fu mined for each 3-tree plot in standard 10-box tubs by measur ture yields. ing the depth of fruit with a calibrated stick inserted through Pounds soluble solids per acre generally followed yields a crossbar placed over the rim of the tub. Each box equals ap per tree, except for citrumelo W-2 which was slightly better in proximately 90 pounds. Approximately 40 fruit were collect cumulative yields than Swingle, but produced less soluble sol ed from each of 3 replications for juice analysis prior to ids per acre than Swingle (Table 2). Trees on rootstock F/80- harvest. Analysis was done by the Dept. of Citrus using com 3 led all other rootstocks in production of pounds of soluble mercial extractors at CREC.