Floral Bud Chill Requirement of Low-Chill Southern Highbush Blueberry Germplasm

The University of Florida southern highbush blueberry (SHB) (Vaccinium corymbosum L. hybrids) breeding program has traditionally focused selection efforts in an area that annually receives >= 300 h of winter chilling at 0 to 7 degrees C. Thus, many of the cultivars released from the breeding program are not adapted to regions in central and south Florida that receive less annual chilling unless dormancy-breaking agents such as hydrogen cyanamide (HC) are used. To assess the potential for expansion into very low-chill production areas, floral bud chill requirements for 23 advanced selections and two cultivars planted at two locations in Florida were estimated using an excised shoot forcing method. The majority (72%) of the genotypes assessed had at least 70% floral budbreak after accumulation of 200 chill-hours at 0 to 7 degrees C. When HC application was compared with untreated plants of the same genotype, the dormancy breaking compound either hastened floral budbrcak or increased the percentage of floral budbrcak of insufficiently chilled plant material.