Germplasm evaluation for crop improvement: Analysis of grain quality and cadmium accumulation in barley

Evaluating genetic variation in barley (Hordeum vulgare) germplasm, combined with genome-wide genotyping, is vital for identifying genes controlling important grain-quality traits. For example, in addition to traditional grain quality properties such as starch and protein contents, grain safety parameters such as heavy metal content, are important in the use of barley for human food and animal feed. A number of genes affecting grain quality have been identified by map-based cloning strategies and functionally analyzed by genetic transformation experiments. Moreover, germplasm evaluation yielded information that enabled the introgression of a key gene controlling grain cadmium accumulation into an elite barley cultivar, reducing the content of this heavy metal in grain. Genotyping of molecular markers and resequencing of germplasm accessions may provide information about how grain quality–related loci evolved and how the current allelic diversity was established. In this review, we describe germplasm resources for barley grain quality–related traits and the methods used to analyze the functions of genes controlling these traits, illustrating cadmium accumulation as an example. We also discuss future directions for the efficient identification of grain quality–related genes.