Novel microsatellite markers for evaluation of genetic diversity in the tetraploid flame azalea, Rhododendron calendulaceum (Ericaceae).

Microsatellite markers have become a popular and useful tool for investigating evolutionary processes at shallow taxonomic scales such as within a species or between extremely closely related species. Rhododendron sect. Pentanthera is a closely related group of deciduous azaleas that demonstrate both naturally occurring and horticulturally derived hybridization. Two species, flame azalea and Cumberland azalea, represent a particularly recalcitrant evolutionary problem, which will benefit from the development of rapidly evolving molecular markers. Microsatellite markers were specifically developed for Rhododendron calendulaceum, the flame azalea, for use in studies of genetic structure and potential hybridization with its close relative Rhododendron cumberlandense, the Cumberland azalea. Forty-eight primer pairs designed from paired-end Illumina MiSeq data were screened for robust amplification. Sixteen of these pairs were PCR-amplified in the presence of fluorescently labeled primers and genotyped in 66 flame azalea individuals from three geographically dispersed populations. Fifteen primer pairs were both reliable and polymorphic and exhibit ample variability for use in downstream population-level investigations. Cross-amplification in all other members of Rhododendron sect. Pentanthera was highly successful, suggesting broad utility across the entire clade. The novel microsatellite markers presented here functioned well within the target species and amplified with high success in the remaining members of the clade. They represent a significant improvement to the genetic toolkit available for Rhododendron sect. Pentanthera, and particularly for the flame/Cumberland azalea evolutionary problem.