LOW CHILL BREEDING OF DECIDUOUS FRUITS AT THE UNIVERSITY OF FLORIDA

Florida’s low chill fruit breeding program was initiated in the early 1950s. Blueberry breeding in Florida has concentrated mainly on developing low-chill, early ripening, tetraploid highbush cultivars. The method has been recurrent selection starting with hybrids between Florida native blueberries (mainly Vaccinium darrowi Camp) and high-chill highbush cultivars (mainly V. corymbosium L.) from Michigan, New Jersey, and North Carolina. Peach breeding utilized South China peaches from the descendants of importations through Charleston, South Carolina, the Hawaiian group, and Okinawa as sources for local adaptation. These were inter-hybridized with the best commercial genotypes, mostly at USDA, Ft. Valley, Georgia, and segregating and backcross generations provided the melting flesh varieties upon which the low chill industry was founded. Non-melting flesh was introduced from Mexico in 1969, from North Carolina in 1972, and from Brazil in 1982. Semi-freestone, low chilling genotypes have been obtained from the 3 sources. Development of the high density fruiting nursery, identifying early ripening from red anthocyanin in autumn leaves, and selection for less blind nodes and bud drop has led to major improvements in the peach breeding program. Undesirable characteristics associated with nonmelting flesh such as long fruit development period, high chill, lack of red skin, off flavor, and low aroma, have been overcome. Improvement in firmness, tree ripe flavor, red skin development as fruit were allowed to ripen on the tree, round fruit shape, short pubescence, and tree ripen flavor were possible with the non-melting flesh. Advances in tree structure, resistance to bacterial spot and leaf rust, and development of ornamental flower and novel fruit types such as peento and anthocyanless fruits have been made. Subtropical plums were developed by crossing a low chill Japanese plum from Taiwan with high chill genotypes at USDA, Byron, Georgia, and because of self incompatibility were carried through 5 polycross generations to produce the ‘Gulf-’ prefix cultivars. The search for subtropical apricots has centered on a low-chill mume from Thailand [(Prunus. mume Sieb. & Zucc. x apricot) F₂], to produce 2 selections that have been open pollinated and backcrossed again to apricots. These seedlings are expected to produce home garden apricot cultivars. Subtropical sweet cherry development is less promising, but a low chill selection of interspecific hybridization has been crossed with sweet cherry and resulting F2 seedlings may produce a home garden cultivar. ‘Anna’ and ‘Dorsett Golden’ subtropical apples have been used in breeding ‘TropicSweet’ in Florida and others in Mexico such as ‘Granny Mex’. Subtropical pears were mainly “sand pears.” ‘Flordahome’, bred in Florida, has “buttery” flesh texture like European pears.

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