Molecular approaches and breeding strategies for drought tolerance in barley

Barley genotypes, in particular landraces and wild species, represent an important source of variation for adaptive traits that may contribute to increase yield and yield stability under drought conditions, and that could be introgressed into improved varieties. Traits that have been investigated include physiological/biochemical and developmental/ morphological traits. Yield performance under drought is particularly a complex phenomenon, and plants exhibit a diverse range of genetically complex mechanisms for drought resistance. Quantitative trait loci (QTL) studies with and without H. spontaneum have shown that developmental genes, notably those involved in flowering time and plant stature show pleiotropic effects on abiotic stress tolerance and ultimately determine yield. Problems associated with the hybridization of H. spontaneum such as alleles with deleterious effects on field performance could be best addressed in the advanced backcross (AB-) QTL analysis. It was interesting to see that in AB-QTL populations like in balanced populations major QTL overshadowed minor QTL-alleles. Nevertheless, crosses with H. spontaneum, AB-QTL populations and association studies with H. spontaneum have also identified new alleles and genes that are related to abiotic stress tolerance. In order to identify genes that are related to drought tolerance microarrays analysis to monitor gene expression profiles for plants exposed to limited water environment is performed.
Several studies with rapid dehydration treatment have shown that osmotic-stress-inducible genes could explain the response to drought stress in plants. Another development is the identification and use of nucleotide polymorphisms (SNP) in genes related to abiotic stress tolerance. An understanding of the combined function and expression of genes involved in various abiotic stresses, could help identify candidate genes underlying QTL of interest.