Generating Genomic Tools for Blueberry Improvement—An Update of Our Progress

There is increased demand for and consumption of blueberries worldwide because of their many recognized health benefits. Great strides have been made in blueberry cultivar development since its domestication using traditional breeding approaches. However, genomic tools are lacking in blueberry, which could be used to hasten improvement. The overall aim of our Specialty Crop Research Initiative project, “Generating Genomic Tools for Blueberry Improvement,” is to develop genomic tools for molecular breeding and assessing genetic diversity of blueberry. Our specific objectives are to develop genomic resources for blueberry, which include expressed sequence tag (EST) libraries, EST-derived molecular markers, and genetic linkage maps in diploid and tetraploid blueberries. We plan to use these markers to identify quantitative trait loci associated with cold hardiness, chilling requirement, and fruit quality traits in highbush blueberry (Vaccinium corymbosum), and in studies of genetic diversity, gene flow, and evolutionary relationships between wild blueberry species. In 2009-2010, transcriptome sequences were generated from highbush fruit at different stages of development, flower buds at different stages of cold acclimation, and leaves by "next generation" 454 sequencing. Over 500,000 sequences were assembled into approximately 15,000 contigs, which are currently being annotated. SSR and EST-PCR primer pairs designed from previously available ESTs were screened for polymorphism in parents of the mapping populations and are being added to each map. Plants from the tetraploid mapping population were propagated and established at various locations. Plants from the diploid mapping population were evaluated for cold hardiness over two years. In a study on gene flow and yield in wild lowbush blueberry (Vaccinium angustifolium), two high- and two low-producing clones from each of two cultivated fields in Maine were used as pollen recipients in hand crosses. Mixtures of pollen from each clone's neighborhood, as well as the other three neighborhoods in that field, were applied in crosses. Interestingly, the lowest producer's yield (fruit set times mean berry weight) was increased by 2-6 times when pollinated by any of the three ‘foreign' pollen neighborhoods as compared to their own neighborhood. A preliminary phylogenetic tree of Vaccinium species in the section Cyanococcus was constructed based on length polymorphisms of EST-PCR markers. The availability of these genomic tools generated as part of this project will allow future advances such as the development of a blueberry microarray to study gene expression, use of marker-assisted breeding in highbush blueberry, and insight into yield differences among wild, lowbush blueberry genotypes.