Impact of Wide Hybridization on Highbush Blueberry Breeding

Abstract

<jats:p>The use of interspecific hybridization in blueberry (<jats:italic>Vaccinium</jats:italic> L. section <jats:italic>Cyanococcus</jats:italic> Gray) breeding has resulted in the incorporation of novel traits from wild germplasm and the expansion of the geographic limits of highbush blueberry (<jats:italic>V. ×corymbosum</jats:italic> L.) production. The objectives of this study were: 1) to estimate the impact of wide hybridization on inbreeding, heterozygosity, and coancestry of the cultivated tetraploid highbush blueberry; 2) to establish the usefulness of microsatellite markers in assessing genetic relationships among southern highbush blueberry [SHB (<jats:italic>V. ×corymbosum</jats:italic>)] cultivars; and 3) to report on the expected genetic contribution of wild <jats:italic>Vaccinium</jats:italic> clones to SHB cultivars. Pedigrees of 107 highbush blueberry cultivars were used to calculate tetrasomic inbreeding coefficients (<jats:italic>F</jats:italic>), pedigree-based genetic distances, and expected genetic contributions of wild clones. Genotyping data from 21 single-locus microsatellite markers screened across 68 genotypes were used to calculate heterozygosity and proportion of shared alleles distances (D<jats:sub>sa</jats:sub>). The results indicated that the effects of wide hybridization on genetic diversity of cultivated blueberry were lower than previously thought. First, SHB cultivars exhibited similar levels of molecular relatedness as historical northern highbush blueberry [NHB (<jats:italic>V. ×corymbosum</jats:italic>)] cultivars (median D<jats:sub>sa</jats:sub> between pairs of cultivars equals 0.19 in both cultivar groups), despite the broader genetic base and larger pedigree distances in the former cultivar group. Second, levels of heterozygosity in modern NHB cultivars were not statistically different from those of SHB (χ<jats:sup>2</jats:sup> = 4.0; df = 3; <jats:italic>P</jats:italic> &gt; 0.05), despite the considerably higher levels of inbreeding in the former cultivar group (median <jats:italic>F</jats:italic> equal to 0.0035 and 0.0013, respectively). Furthermore, pedigree-based genetic distances were significantly correlated with D<jats:sub>sa</jats:sub> (<jats:italic>r</jats:italic> = 0.57, <jats:italic>P</jats:italic> ≤ 0.0001), indicating that microsatellite markers are reliable tools in most cases to assess the genetic relationships among SHB cultivars. Finally, seven <jats:italic>Vaccinium</jats:italic> species constitute the current genetic base of cultivated SHB. In this article, we report on the expected genetic contributions of <jats:italic>V. angustifolium</jats:italic> Ait., <jats:italic>V. constablaei</jats:italic> Gray, <jats:italic>V. corymbosum</jats:italic>, <jats:italic>V. darrowii</jats:italic> Camp, <jats:italic>V. elliottii</jats:italic> Chapman, <jats:italic>V. tenellum</jats:italic> Ait., and <jats:italic>V. virgatum</jats:italic> Ait. (syn. <jats:italic>V. ashei</jats:italic> Reade) clones to 38 SHB cultivars.</jats:p>

Adventitious shoot regeneration from leaf explants of southern highbush blueberry cultivars

“…In addition, transgenic 'Legacy' plants with herbicide resistance have been produced and field trials have been carried out (Song et al 2007(Song et al , 2008. However, with the wide differences in genetic composition of southern highbush cultivars (Brevis et al 2008;Ballington 2009), systematic studies are still needed to optimize regeneration systems for individual cultivars. In the present study, we developed efficient regeneration systems for four selected southern highbush cultivars using leaf explants and found that both cultivar source and physiological status of leaf explants affected shoot regeneration.…”

Reaction of Different Vaccinium Species to the Blueberry Leaf Rust Pathogen Thekopsora minima

“…In addition, it is important to characterize the existing breeding selections before they are released or used in crossing. Southern highbush blueberry possesses genes introduced from several Vaccinium species (Brevis et al, 2008). Two tested accessions of V. arboreum displayed immunity against T. minima.…”

“…Southern highbush blueberry cultivars possess genes introduced from several Vaccinium species, including V. darrowii Camp, V. angustifolium Ait., V. virgatum Ait., V. elliottii Chapm., V. tenellum Ait., V. pallidum Ait., V. myrsinites Lam., and V. stamineum Lam. (Brevis et al, 2008;Ehlenfeldt et al, 1995;Hancock et al, 1995;Yousef et al, 2014). Relatively little is known about the reaction of commercial blueberry cultivars and native diploid Vaccinium species to T. minima.…”

Ovule Culture and Embryo Rescue Facilitate Interspecific Hybridisation in Blueberry (Vaccinium Spp.)

“…V. angustifolium is well adapted to colder climates, is low maintenance with low agrochemical input requirements because of its high degree of pest resistance, and is well suited to mechanical harvesting (Janes and Percival, 2003;Yarborough, 2012). Hexaploid cultivars belonging to V. ashei have greater plant vigour and yield, tolerance of a wider range of soils, and greater fruit firmness, giving longer shelf-life of harvested fruit (Brevis et al, 2008).…”