temperature, and light intensity on the growth of lowbush blueberry and ion translocation in wheat. Physiol. Plant. 39:305-310. (Vaccinium anguslifolium A.t.) Can. J. Bot. 39:1733-1739. 21. Orchard, B. 1980. Effect of root and air temperature on growth and 16. Hussan, M. M. and F. M. Basiouny. 1984. The use of metabolic in yield of tomatoes. Acta Hort. 98:19-28. hibitors, film-forming antitranspirants, and maxijet irrigation to in 22. Pallars, I. E. Jr. 1960. Effects of temperature and humidity on foliar crease yield, improve quality and water use efficiency of blueberries. absorption and translocation of 2,4-dichloropheroxyacetic acid and Proc. Fla. State Hort. Sci. 97:348-350. benzoic acid. Plant Physiol. 35:575-580. 17. Locasio, S. J. and G. F. Warren. 1960. Interaction of soil temperature 23. Spiers, J. M. 1983. Influence of N, K and Na concentration on growth and phosphorus on growth of tomatoes. J. Amer. Soc. Hort. Sci. and leaf element content of Tifblue' rabbiteye. HortScience 18:223- 75:601-610. 224. 18. McNairn, R. and H. B. Currier. 1968. Translocation blockage by 24. Spiers, J. M. 1978. Effects of pH level and nitrogen source on ele sieve plate callose. Plana 82:369-380. mental leaf content of 'Tifblue' rabbiteye blueberry. J. Amer. Soc. 19. Moorly, J. and C. J. Graves. 1980. Root and air temperature effects Hort. Sci. 103:705-708. on growth and yield of tomatoes and lettuce. Acta Hort. 98:29-43. 25. Webster, D. H. 1965. Heat-induced callose and lateral movement of 20. Nordin, A. J. 1977. Effect of low root temperature on ion uptake assimulates from phloem. PhD Diss., Univ. Calif., Davis. Proc. Fla. State Hort. Soc. 98: 158-162. 1985. BREEDING BLUEBERRY CULTIVARS FOR THE CENTRAL FLORIDA PENINSULA P. M. Lyrene and W. B. Sherman the central peninsula of Florida. Two factors make this University of Florida, IFAS prospect interesting. One is the large potential U-pick mar Fruit Crops Department ket available around population centers in the region and Gainesville, FL 32611 the second is the possibility of producing blueberries for shipment during April, when no other fresh blueberries Additional index words. Vaccinium ashei, Vaccinium corym- are available. bosum, pentaploids, chilling requirement. 'Sharpblue' (19) is currently believed to be the cultivar best adapted to the area south of Ocala, although grower experience with blueberries in this area is not sufficient to Abstract. Wild highbush blueberries (Vaccinium corymbosum allow firm conclusions. For the U-pick market, where early L) occur in woodland sites in the central Florida peninsula ripening is less important, some of the currently available southward to Lake Okeechobee. This suggests that commercial rabbiteye cultivars may also prove satisfactory. blueberry production should be possible in the area if suitable cultivars are developed. Two potentially profitable markets The purpose of this paper is to discuss the prospects for growing blueberries in the central Florida peninsula are the local U-pick market and the April fresh-fruit shipping market. Consistent production of blueberries during early to and to describe some breeding strategies that could result in cultivars that would perform better in the area. mid April will require production sites where the last killing frost is 15 Feb. or earlier. Cultivars for this purpose must Blueberry Cultural Problems In The Central Florida Peninsula flower early and have short flowering-to-ripening intervals. For the U-pick market, high yields are more important than Climate. The climate between 1 Nov. and 1 Mar. is the early ripening. Possible selections for U-pick production, in primary reason for uncertainty regarding the performance clude rabbiteye blueberries (V. ashei, Reade) selected for re of north-Florida blueberry cultivars in the central Florida sistance to mild-winter-induced fruit drop and fruitful pentap- peninsula. The 2 cultivated types, highbush and rabbiteye, loid hybrids, which combine the high plant vigor of the rab are deciduous in north Florida. Flower buds ordinarily be biteye with the highbush ability to set fruit well following come visible in the leaf axils during Sept., Nov., and Dec. insufficient chilling. The leaves begin to abscise after the first killing frost, and plants usually lose most of their leaves by 1 Jan. North- Blueberry production is expanding rapidly in North Florida blueberry cultivars have a chilling requirement of America. In 1935 there were fewer than 1,000 acres of about 200 to 300 hr below 45°F for 'Sharpblue' and 200 to cultivated blueberries on the continent, but estimates in 500 hr for various rabbiteye cultivars. Plants that have been 1983 placed combined cultivated acres of highbush and inadequately chilled usually show delayed bud break in the rabbiteye blueberries at 39,050 (15). Florida's acreage of spring. Some buds may open and grow, while others on cultivated blueberries has increased from fewer than 200 the same stem remain dormant, flowering may be delayed to almost 1,000 acres within the past 10 years, and the rate a month or more, and the flowering period may be pro of expansion is accelerating. Almost all of this acreage has longed. Berry ripening also will begin later than normal been planted from Ocala northward, where current cul and extend over a longer period. Plants may lose vigor and tivars are best adapted and have been tested most exten die if underchilling is severe and occurs for several years. sively (16,17,18). Poor fruit set is another effect of insufficient chilling Although their fruit is too small for commercial use, at (10). This is very important with many rabbiteye cultivars least 3 species of native wild blueberries, V. darrowi Camp, but much less so with highbush. Following mild winters, V. myrsinites Lam., and V. corymbosum are abundant on acid some rabbiteye cultivars flower normally, but set few fruit, soils as far south as Lake Okeechobee (1,11,12,20). This the young berries abscising shortly after petal fall. This indicates that blueberry cultivation should be possible in phenomenon is poorly understood, and it it is not clear why the problem is so much more severe with rabbiteyes University of Florida Journal Series Number 6841. than with highbush. The severity of mild-winter-induced 158 Proc. Fla. State Hort. Soc. 98: 1985. fruit drop varies considerably among rabbiteye cultivars. veloped with a bloom-to-ripe interval as short as 50 days, Other problems with climatic adaptation might be an dependable berry production in early April will probably ticipated when north-Florida blueberry cultivars are grown require cultivars that flower earlier than 'Sharpblue'. Such south of their region of best adaptation. During a very cultivars would not be adapted to north Florida because mild winter, vigorous plants might continue to grow the danger of crop loss from spring frost would be too throughout the winter without losing their leaves. This great. Table 1 shows for selected cities in north and central could result in nonsynchronous flowering. After the nor Florida the date after which chances are 80% that temper mal fruit harvest in May, vigorous 'Sharpblue' at Gaines atures lower than 28°F will not occur (14). This is the ap ville sometimes flower a second time during the summer proximate date on which a grower might wish his blueber and fall. The resulting fruit is usually destroyed by frost ries to flower if he were growing for the early market and in November. When grown farther south, 'Sharpblue' did not have overhead irrigation for frost protection. might ripen this fruit during the winter if protected from Overhead irrigation at 0.2 acre-inches/hr could protect frost. flowers and fruit down to 22°F if winds were light. With 'Sharpblue' and other low-chilling highbush cultivars overhead irrigation, optimum flowering dates would be could be somewhat vulnerable to frost in central Florida. earlier than those shown in Table 1. If the first part of the winter season was cold, and warm Care must be taken in using Table 1 due to localized weather followed during Jan. and early Feb., the plants variations in last-frost dates. A location even within a few could flower by 10 Feb. and be vulnerable to spring frost. miles of the weather station may differ significantly in frost The opposite problem with trying to produce early-season occurrences because of local topographic features.The im berries would occur in years when flowering and fruiting portance of local variation is illustrated by Sanford and dates were delayed excessively due to lack of chilling. Deland (Table 1), which are less than 20 miles apart but The greatest challenge in trying to breed blueberries differ in average date of last 28°F temperature by 26 days. for the central peninsula is not lack of chilling per se, since Longtime residents often know from experience whether low-chilling genes are available in native blueberries. The their locations are warmer or colder than official recording greatest challenge is the high year-to-year variability in the locations. amount of chilling received and the variability in timing of Average temperatures for December, January, and the chilling period. Native species cope with this variability February indicate how much chillling plants receive. Areas by coupling evergreen growth habit with late flowering or with temperatures averaging 59.0°F or below from 1 Dec. by having a long flowering period. Neither strategy is very through 28 Feb. should be able to get good yields on low- satisfactory for a breeder if his goal is to produce early-ri chill rabbiteye cultivars in most years. This expectation is pening blueberries with synchronous ripening. based on several years' observations of blueberry farms in Other cultural problems.