No abstract

Due to lack of water resources in irrigated agriculture, genetically improving plants to abiotic stresses such as salinity is a necessity for food and feed production. In this respect, the new third man-made amphiploid cereal, tritipyrum (2n=6x=42, AABBE, is an example which is capable of tolerating a high level of NaCl. In order to determine the salinity tolerance mechanisms of this new cereal, an experiment was conducted using hydroponic technique. Ten tritipyrum lines and two wheat cultivars were tested under three levels of salinity (50, 100 and 200mM NaCl). The effect of salinity stress on Na + and K + concentration of leaf, shoot and root, proline and chlorophyll content were measured at 50% ear emergence and their grain yield plant -1 was evaluated at physiological maturity. Leaf Na + concentration in tritipyrum lines increased with increasing salinity while K + concentration did not show any especial pattern. The chlorophyll and proline content in tritipyrum lines were higher than that of wheat cultivars. Despite the high sodium concentration in tritipyrum lines in comparison with wheat, the grain yield of tritipyrum lines were less affected than that of wheat. There was also a negative correlation between proline content and grain yield plant -1 in tritipyrum lines. It can be concluded that mechanisms such as higher Na + uptake along with appropriate ion compartmentation could be used by tritipyrum lines to combat with salt stress like some halophytes and it can make tritipyrum lines suitable for planting in saline soils and improving the salinity tolerance of wheat. Keywords:Halophytic wild ancestors, Proline, Salt tolerance mechanism, Tritipyrum. Abbreviations: LNa_ leaf sodium concentration; LK_ leaf potassium concentration; LK:Na or L K + /Na + _ leaf potassium to sodium ratio; SN_ stem sodium concentration; SK_ stem potassium concentration; SK:Na_ stem potassium to sodium ratio; RN_ root sodium concentration; RK_ root potassium concentration; RK:Na_ root potassium to sodium ratio; Chl a_chlorophyll a concentration; Chl b_ chlorophyll b concentration; Chl a/b_ chlorophyll a to chlorophyll b ratio; T Chl_ total chlorophyll; GY_ grain yield plant

The novel salt tolerant cereal, Tritipyrum, was suggested as a potential species for cultivation in saline soils to improve s alt tolerance in wheat via breeding programs. Hence, investigation of its reaction to salinity stress, especially at different growth stages, seems to be necessary. For this purpose, an experiment was conducted using hydroponic technique in controlled as well as field conditions. Nine tritipyrum lines were tested under three levels of salinity (50, 100 and 200 mM NaCl) in hydroponic culture. Then, based on the results, three tritipyrum lines along with one wheat cultivar were cultivated in the field under three levels of salinity of irrigation water (control, 7dS/m and 14dS/m). In the hydroponic test, according to the statistical analysis of the genotypes based on their vegetative, reproductive and seed maturity traits, tritipyrum lines were more salt tolerant than salt tolerant wheat cultivar. Also cluster analysis showed that (St/b)×(Cr/b), F4 and Az/b were the most salt tolerant tritipyrum lines. Furthermore, based on the field trial, tritipyrum lines showed better performance and produced higher grain yield as well as higher grain protein content than wheat cultivar in saline condition. Based on our results, it is conceivable to improve the salt tolerance of wheat through breeding programs. Tritipyrum lines can also be cultivated in saline soils as fodder or forage crop.

Mechanisms of salt tolerance in tritipyrum, a promising achievement of breeding programs against the deleterious effects of salinity stress, have not been fully explored. Therefore, we conducted a greenhouse experiment with four tritipyrum lines and one wheat cultivar under four salinity levels (0, 60, 120 and 180 mM NaCl), in hydroponic condition. Sampling for physiological traits was conducted in 48 hours, one week and one month after exposure to salinity treatment. The results showed that tritipyrum had more chlorophyll pigments and carotenoid than wheat. Furthermore, concentration changes of proline and carbohydrate was more prominent in tritipyrum than in wheat; superoxide dismutase and catalase as well as peroxidase and ascorbate peroxidase activity were lower in Az/b and (Ka/b)*(Cr/b), F 6 than in Cr/b and wheat; lower malondialdehyde in Az/b and (Ka/b)*(Cr/b),F 6 indicated higher salinity tolerance of these hybrids compared with wheat and Cr/b; it was also found that different genotypes used various defense mechanisms to adapt themselves to salinity. Other defense mechanisms such as developed photosynthetic machinery, better activity of non-enzymatic antioxidant systems and higher accumulation of compatible solutes can be more effective than antioxidant enzymes in higher salt tolerance of tritipyrum lines. Our results indicate that non-enzymatic defense systems are more important than enzymatic ones in tolerating salinity stress in tritipyrum lines. Furthermore, in comparison with wheat, higher salinity tolerance of tritipyrum lines, especially Az/b, can make them suitable for the improvement of salinity tolerance of common wheat by breeding programs.