Advances in strawberry breeding at the University of Florida

In the last three years, the strawberry breeding program at the University of Florida (UF) has sought to implement genomics-assisted breeding. Continuing a long history of cultivar releases for subtropical and Mediterranean climates, development of new cultivars with improved flavor, fruit quality, early yield and disease resistance is being accomplished by combining traditional field breeding with DNA-based tools. In collaboration with the RosBREED consortium, a combination of high-throughput genome scanning and pedigree-based quantitative trait locus (QTL) analysis has been the strategy of choice for discovering and exploiting genetic loci with meaningful effects in breeding populations. Examples of large-effect QTL for resistance to three strawberry diseases are: angular leaf spot caused by Xanthomonas fragariae [locus Xf1 on linkage group (LG) 6D], crown and root rot caused by Phytophthora cactorum (Pc1 on LG7D), and crown rot caused by Colletotrichum gloeosporioides (Cg1 on LG6B). Moderate-effect QTL include those identified for soluble solids content (LG6A) and fruit size (LG6C and LG4B). These five QTL, discovered in UF germplasm totaling more than 1,100 individuals from 122 full-sib families, were validated in sets of advanced selections totaling more than 600 individuals. Haplotype information was utilized in the selection of all parents and crosses in 2015, and marker-assisted seedling selection was performed on ~8000 seedlings using two previously developed DNA tests: a high-resolution melting (HRM) analysis for fruity aroma (γ-decalactone) and an SSR marker for perpetual flowering. HRM tests for Pc1 and for Xf1 were added in 2016, to screen ~30,000 seedlings. Finally, the development and application of genomic selection methodology will also be discussed as a complementary strategy for complex, polygenic traits in strawberry.