Novel germplasm resources for improving environmental stress tolerance of hexaploid wheat

Wheat (Triticum spp. L.) breeders have significantly improved wheat adaptation to stress-prone environments around the world. This progress has largely been achieved using empirical selection and genetic variability within the primary wheat gene pool. As most stress tolerance traits are quantitatively inherited, expansion of the available genetic diversity for stress tolerance is necessary if rates of genetic progress are to be maintained. This review explores three sources of novel genetic variability, namely synthetic wheat, landrace cultivars, and alien introgressions and their applicability to applied wheat breeding. Synthetic hexaploid wheat, derived by crossing tetraploid wheat with Aegilops tauschii, provides new genetic variability for adaptation to drought, high temperature, salinity, waterlogging, and soil micronutrient imbalances from the secondary wheat gene pool. Synthetic-derived materials have performed well in many stressed environments globally. There is significant unexploited variation among landraces and modern wheat cultivars to improve the stress adaptation of cultivated wheat. The tertiary gene pool, with a few significant exceptions, has been more difficult to exploit due to complex inheritance, meiotic instability, and linked deleterious effects. Nevertheless, there is sufficient genetic variation in the wheat gene pool to ensure the continued improvement of wheat adaptation to abiotic stress.