Detecting Local Adaptation for Rhizosphere Acidification in a Wild Deciduous Azalea Species

Measures of genetic differentiation provide useful benchmarks by which to compare quantitative trait differentiation in woody species. These analyses, typically known as Q_st-F_st comparisons, can infer whether a quantitative trait is locally adapted in a population. Such experiments produce not only ecological insights, but useful breeding directions and identify new germplasm sources for quantitative traits of interest. We set out to determine the genetic differentiation in a wide-ranging deciduous azalea Rhododendron viscosum (L.) Torr, a species of breeding interest due to its late bloom and general abiotic stress tolerance. We identified seven broad subpopulations across the southern United States from Arkansas to Florida encompassing a variety of environments. We developed 14 SSR loci from a sequenced R. viscosum bud transcriptome for estimations of subpopulation genetic differentiation based on F_st and R_st statistics. We compared this to the quantitative trait differentiation of rhizosphere acidification, a candidate trait for pH adaptability in deciduous azalea. To determine if rhizosphere acidification was locally adapted, we estimated the trait Q_st value, or ratio of trait additive variance among versus within subpopulations, from the progeny of 19 maternal half-sib families. Though rhizosphere acidificaiton was not locally adapted, we consider this research to be a blueprint for investigating novel, quantitative traits in uncharacterized woody species.