QTL Mapping in an F1 Tetraploid Blueberry (Vaccinium corymbosum L.) Population

Worldwide demand for highbush blueberry (Vaccinium corymbosum L.) is rapidly growing, due in part to high consumer demand for its many health benefits.  Marker assisted breeding techniques are currently being developed to aid in more efficient development of improved cultivars with increased nutritional content and overall plant fitness in varying chill environments. To study the relationship of many commercially important traits, a cross between northern highbush ‘Draper’ and southern highbush ‘Jewel’ was made to produce a segregating F₁ population of 105 individuals. The population was clonally propagated and planted at four U.S. locations in 2009; Interlachen, FL; Manor, GA; Corvallis, OR; and Grand Junction, MI.  Eighteen traits were evaluated in 2011 using objective measures and subjective scores for segregating characteristics relating to winter chilling, overall plant characteristics, flowering times and fruit quality traits.  Analysis of segregation was performed on ‘Draper’, ‘Jewel’, and 90 F₁ individuals.  The draft map of ‘Draper’ resulted in 287 loci composed of 158 co-dominant SSRs and 129 SSRs scored as dominant markers. Cluster analysis in TetraploidMap was used to construct the current fifteen linkage groups, and a multipoint analysis was used to order the groups and calculate LOD scores and recombination frequencies between loci.  Genstat was used for a preliminary QTL analysis using phenotypic data generated in Florida and Georgia.  Multiple putative QTLs were identified for pedicel scar size, soluble solids content, and total titratable acids at P < 0.01; and berry weight, plant width, overall yield, and proportion of vegetative buds that broke at P < 0.001. The QTLs identified in this study will be confirmed across different locations and years for the 2011 and 2012 data. After QTL regions are confirmed, increased marker coverage will be targeted to these areas to identify genes controlling these traits.  The molecular breeding tools developed from this research will be disseminated to blueberry breeders in the academic and industrial sectors to assist in more efficient development of improved cultivars.