This study presents the first data on the drought resistance pattern of seven new synthetic 6x primary Tritipyrum amphiploid lines and evaluates their mitotic instability. The primary Tritipyrum lines were crossed with Iranian 6x bread wheat 'Navid' cultivar and their F 1 and F 2 progenies were obtained. Two experiments with complete randomized design were conducted under optimum and limited water conditions to evaluate Tritipyrum-derived genotypes for drought resistance in greenhouse. Under optimum water conditions, grain yield, numbers of grains per spike and harvest index of Tritipyrum-derived genotypes were significantly lower than bread wheat; however the differences were not significant under limited water conditions. These results showed the better responses of Tritipyrumderived genotypes to drought conditions. Evaluation of leaf osmotic and water potentials and drought susceptibility index showed that drought resistance of Tritipyrum and F 1 genotypes was significantly higher than that of bread wheat and Triticale. Cytological investigations showed that Tritipyrum-derived genotypes aneuploidy was significantly higher than Triticale and bread wheat (p<0.05). Mitotic instability in light grains (1000-grains weight < 30 gr) was significantly higher than heavy grains (1000-grains weight > 30 gr) in parental and F 2 genotypes (p<0.01). Aneuploidy has showed a significant negative correlation with fertility, grain yield and 1000-grains weight in Tritipyrum genotypes. In general, Tritipyrum may complement the role of bread wheat in arid and semi-arid regions; but further breeding research is needed to overcome its mitotic instability.

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