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Genes from virtually all the native species of blueberry have been incorporated into the northern highbush background, but the most useful native clone of all has been Florida 4B, a selection of diploid Vaccinium darrowi. Florida 4B was particularly instrumental in reducing the chilling requirement of the northern highbush, but it has also proven to transmit exceptionally high fruit quality, vigor, heat tolerance and adaptation to mineral soils (1, 3, 6). To date, its genes are in the background of 11 southern cultivars, and it shows high promise as a northern breeding parent.
The name of the species was given by the blueberry taxonomist, W.H. Camp to honor George M. Darrow who first recognized it as a specific entity (2). Dr. Darrow, USDA-ARS small fruit breeder, and Ralph Sharpe, University of Florida blueberry breeder, selected Florida 4B from the wild in Central Florida. Dr. Darrow related (personal communication) that they were driving near Tampa, Florida and saw from the highway a vigorous and outstanding V. darrowi plant growing in a pasture adjacent to the road. They stopped, took cuttings and gave it the designation Florida 4B.
In 1966, a series of blueberry crosses were initiated at Beltsville, Maryland to produce seedling populations adapted to low-chilling areas (500-900 winter hours below -7[degrees] C) in the Gulf Coast region of southeast U.S. The tetraploid highbush blueberry (V. corymbosum) with a rather lengthy history of genetic improvement has large, flavorful fruit, but a high chilling requirement (greater than 1,000 hours below -7[degrees] C) and does not succeed in low-chill areas. The breeding objectives were to originate tetraploid blueberry seedling populations that had highbush blueberry fruit quality, but were adapted to the soils and climate of southeast U.S. This type of blueberry later became known as southern highbush.
Plants of several southern diploid Vaccinium species, V. elliottii, V. tenellum, V. atrococcum, V. darrowi, tetraploid V. myrsinites and hexaploid V. ashei were used in our crosses at Beltsville to obtain southern adaptation (4, 5, 6). At the time, blueberry breeders generally did not intercross Vaccinium species due...