Breeding strategies for structuring salinity tolerance in wheat

The wheat gene pool has a tremendous amount of genetic diversity for salinity tolerance. During the last few decades, several wheat genetic stocks have been developed showing all three types of tolerance mechanisms, i.e., tissue tolerance, osmotic tolerance and ion (Na+) exclusion. However, delivery of improved crop varieties adapted to saline conditions has been lagging behind due to several reasons including the huge knowledge gap in understanding genetic basis of salinity tolerance in wheat, and then applying the available knowledge to deliver salt-resilient crop varieties. We review the research around salinity tolerance in wheat in context of historical and rapidly evolving breeding technologies and discuss the future prospects. The extensive research on identifying promising resources of salinity tolerance in durum wheat, synthetic hexaploid wheats and tertiary gene pool species such as those of Thinopyrum have been explored to transfer salinity tolerance traits to bread wheat. As the last few years witnessed leading-edge transformations where we have now (i) new and improved genotyping assays in form of SNP arrays and next-generation sequencing to facilitate gene discovery, (ii) new generation turn-over methods to get five to six generations per year by "speed breeding" facilitating gene deployment, (iii) gene-editing tools to precisely manipulate the effects of causal genes, and (iv) new phenomic platforms for capturing salinity effects in field and glass-house conditions. Integration of all these technologies will help in understanding the complex genetic architecture of wheat adaptability in saline soils and will accelerate the delivery of our future potential wheat cultivars.