Manganese (Mn) deficiency remains an unsolved nutritional problem affecting crop production worldwide. The tolerance to Mn limiting conditions, known as Mn efficiency, is a quantitative abiotic stress trait, generally controlled by several genes. However the underlying genetic background of Mn efficiency remained elusive. This PhD study aimed to understand better the genetic determination of the trait and propose new insights for plant breeding purposes. Two genome-wide approaches were used in a winter barley collection to characterize the genetic control of the trait. First, a Genome-wide association
study (GWAS) and chlorophyll a fluorescence phenotyping allowed to identify several QTLs involved in the plant response to Mn deficiency. Multiple candidate coding genes were fund, among which, photosystem II PsbP subunit, germin-like proteins or Mn-Superoxide Dismutase. It supports the Mn functionality in Mn dependent pathways and processes. In a the second step, a genuine statistical method to assist breeding programs in selecting new varieties, named Genomic Selection (GS), was applied. It was demonstrated that GS is an effective tool to be used in breeding programs for selecting more efficient varieties for Mn efficiency. The obtained results, using the two different genome-wide approaches, provided useful information for future barley breeding for Mn efficiency. Moreover candidate genes identification opened perspectives for a better characterization of Mn efficiency trait at the genome level.