Genome-wide association of gene regions controlling selenium and magnesium accumulation in walnuts (Juglans regia L.)

Walnut (Juglans regia L.) is one of the most economically important species. It is of great importance to the food industry due to its nutritional value, and high content of many beneficial components such as macro and microelements. In the current study, the aim was to determine markers of single nucleotide polymorphism (SNP) associated with the gene(s) controlling the accumulation of Selenium (Se) and Magnesium (Mg) in walnuts. Se and Mg concentrations were measured in 154 genotypes of Juglans regia in 2021 and 2022. A total of 16,473 SNP markers were used for association mapping to analyze the marker-trait associations. The Se and Mg concentrations exhibited a normal distribution pattern with high heritability values (0.96 for Se and 0.98 for Mg) for the two years. Association mapping analysis was carried out with TASSEL software (v5.2.87) using the mixed linear model method. The result was that 17 markers for Se and 15 markers for Mg were significantly associated. A total of 189 and 86 putative candidate genes were detected for markers significantly associated with the Se and Mg levels, respectively. Among these genes, 33 genes are involved in ion binding, one gene in the binding and transport of Mg ions, 10 in hormone metabolism, and 53 in DNA and RNA binding. These potential candidate genes and markers observed in this study can be used in marker-assisted breeding programs to improve biofortified walnut varieties and further explore the genetic mechanisms underlying the Se and Mg accumulation.