Breeding for salt tolerance in wheat: The contribution of carbon isotopic signatures

Use of low-quality water for supplemental irrigation is expected to become soon a common practice in the Mediterranean area, where durum wheat is the main cultivated cereal. Breeding for salt stress tolerance may contribute to the improvement of wheat resilience to irrigation with brackish water. Various traits can be considered as indicators of salt stress tolerance, which include agronomical and physiological criteria. However, the complexity of salinity tolerance mechanisms, the G × E interaction and the lack of correlation between controlled and open field conditions causes uncertainty in the selection process. The present review highlights the main advantages and limitations of different agronomical and physiological traits used in screening for salt stress tolerance in wheat. Special focus is given to carbon and nitrogen isotope discrimination, that remains a bottleneck in breeding for salt stress tolerance. The use of different statistical tools to analyse data related to salt stress tolerance is also discussed in this review.