Genome scan of Kenyan Themeda triandra populations by AFLP markers reveals a complex genetic structure and hints for ongoing environmental selection

Tropical and subtropical rangeland systems provide core ecosystem services for the welfare of human populations that rely on readiness and quality of forage resources. However, forage species are still widely overlooked by molecular biology studies. In the present study, we employ 366 AFLP markers to provide the first description of the genetic landscape of three Kenyan populations of Themeda triandra Forssk., a key wild grass forage species. By including Australian T. triandra accessions and other closely related species in a molecular phylogeny, we provide a first evaluation of the relationships existing between African and Australian germplasm. Genetic diversity, population genetic structure and recombination rates in Kenyan T. triandra populations were investigated in detail. GPS coordinates of each sampled population were used to retrieve meteorological data at specific locations, and environmental factors likely contributing to T. triandra genetic differentiation were taken into consideration using a correlative approach based on outlier loci distribution. The use of molecular markers unveiled some previously unknown aspects about the biology of T. triandra, namely: i) African and Australian T. triandra genotypes analyzed in this study are genetically undistinguishable, ii) sexual recombination of Kenyan T. triandra is likely to play a major role in its reproduction, and iii) environmental characteristics of the collection sites are correlated with the allelic distribution of a limited set of loci under selection.