The 2011 ASHS Annual Conference

Once a plant enters dormancy, accumulation of adequate chilling is a key component necessary for the onset of normal reproductive and vegetative development.  The range of chilling accumulation required for highbush blueberry (Vaccinium corymbosum L.) cultivars varies from near 150 hours at 0-7°C to greater than 1,000 hours.  Knowledge of the chilling requirement for a blueberry cultivar is critical to properly identify the climatic range suitable for production.  To determine the quantitative trait loci (QTL) associated with chilling requirement, an intra-specific cross between the northern highbush ‘Draper’ (> 800 hr chill requirement) and southern highbush ‘Jewel’ (< 200 hr chill requirement) was made to create a segregating F₁ population consisting of 105 individuals.  Plants were then clonally propagated by semi-hardwood cuttings in 2007 and planted in four U.S. locations in 2009.  The locations were selected based upon varying degrees of total chill hours and winter temperatures and include: Gainesville, FL; Manor, GA; Corvallis, OR; and Grand Junction, MI.  The chilling requirement of each individual in the population was calculated by budbreak of potted plants removed from an unheated greenhouse after 50 chill-hour intervals using a modification of the Utah Chill Unit Model for peach. The impact of insufficient chill accumulation was expected to be greatest at the Georgia and Florida sites; however, abnormally cool winter temperatures resulted in higher than normal chill accumulation by March 1, 2011, particularly in Florida (approx. 300 hours average, 580 hours in 2011).  Thus, we had the unique opportunity to study the interplay between chill hour requirement and fruit development period at the Georgia and Florida locations.  Plants in Georgia and Florida were evaluated for all segregating characteristics related to fruit development period in 2011, including flower and leaf developmental stages, overall plant characteristics, fruit quality traits, and post harvest quality.  Variation was observed within and between locations suggesting environmental and genetic control over traits related to fruit developmental period.  The observed phenotypic variation present in this population will be used for future QTL studies to enable the identification of genomic regions associated with these traits, with the ultimate goal of developing marker-assisted breeding strategies to select for variation in fruit developmental period.