Successes In Breeding Blueberries for Low-Chill Environments

In 1948, Ralph Sharpe began a program to develop low-chill highbush blueberry cultivars for Florida. High chilling requirement was known to be a principal  reason why northern cultivars grew poorly in Florida. The tetraploid Florida cultivars were developed by phenotypic recurrent selection, now in the 7^th to 8^th generation, that began with a population produced by crossing tetraploid highbush cultivars from Michigan and New Jersey with low-chill diploid, tetraploid, and hexaploid Vaccinium species from Florida and south Georgia. At first, progress was slow due to the low horticultural quality and long fruit-development period of the Florida native species, and the crossing barriers imposed by differences in chromosome numbers. Growing large seedling populations under field conditions at the location where it was intended to start the commercial industry, and rapidly turning the generations, resulted in rapid improvements in local adaptation, including lower chilling requirement, better adaptation to the long growing season, adequate flower bud initiation despite high autumn temperatures, and resistance to the diseases and insects particular to the region. As adaptation improved, strong selection pressure was simultaneously applied to obtain earlier ripening, higher yields, and better fruit quality, including the ability of the berries to maintain good flavor and texture under warm, humid conditions. Little time was spent studying the underlying genetic and physiological changes, but 8 generations of selecting plants that worked well in commercial fields gave cultivars that have been commercially successful. Depending on the location and the system of management, many of the Florida cultivars can be grown either with the traditional deciduous system or as evergreen plants, in which the leaves of the previous summer support the developing crop through harvest the following spring.