The integration of population genomics and association mapping using a landrace meta-population and historical data on commercial varieties elucidates the genetic basis of adaptation to Mediterranean conditions in barley (Hordeum vulgare L.)

Identifying the genomic regions responsible for the adaptation to different agroecological conditions and subtending environmentally adaptive phenotypic traits is a fundamental task for biologists, geneticists, and breeders. This Ph.D. thesis reports the results of different but complementary experiments carried out to understand plant adaptation processes. The evolutionary history of a barley landrace metapopulation collected in Sardinia, Italy, and evolved under Mediterranean conditions was exploited together with historical data recorded on commercial varieties grown in the same environments. Two main objectives were pursued. The first was to investigate the level and structure of the genetic diversity of barley landrace populations and to determine how this diversity was shaped. To accomplish this task, the role of the different evolutionary forces (genetic drift, migration, and selection) in shaping the current germplasm diversity has been studied. The second objective was to decipher the genetic basis of barley adaptation to diverse environmental and agro-ecological conditions (for bioclimates, latitude, and crop use). Several population genomic analyzes and signatures of selection mapping methods were integrated. Phenotypic characterisations of diverse plant materials and comparative genome-wide association studies were performed. Genomic maps of regions putatively under divergent selection and associated with environmentally adaptive traits such as heading date, plant height, leaf width, erect/prostrate growth habit, thousand-kernel weight, kernels per m2, and grain yield have been produced. The role of candidate genes comprised in these regions has been discussed. The genomic regions identified will support the breeding of new varieties better adapted to current environmental conditions and future climate changes and the implementation of appropriate strategies for the conservation of agrobiodiversity.