Evaluation of osmotic stress tolerance in durum wheat (Triticum durum L.) advanced lines

Introduction Wheat is one of the most important and strategic products and is the most valuable food for the people of the world, especially the Third World countries. Wheat farms in arid and semiarid regions in rainfed conditions are generally exposed to drought stress at the germination, emergence and the late stages of the growing season. The effects of PEG simulated osmotic stress on morphological traits, such as root and stem length, fresh and dry weight of root and stem have been studied in a large number of previous studies. This research was conducted to investigate the effect of osmotic stress on morphological characteristics of advanced durum wheat lines and to classify the studied lines in terms of osmotic stress tolerance and to identify the susceptible and tolerant lines. Materials and methods In order to study the effect of osmotic stress in durum wheat lines, 83 lines were evaluated at two levels including zero (control) and -4 bar osmotic potential. The experiment was done in tow condition based on completely randomized design with four replications. Polyethylene glycol 6000 was used to create -4 bar osmotic potential. The lines were cultivated in plastic pots with 10 cm diameter and 50 cm height that filled with sand. Irrigation of all pots until germination of seeds was done by normal water. After germination stage, control pots irrigated with Hogland solution and under stress pots irrigated with Hogland solution contain PEG6000. The Measurement of morphological traits included root and shoot length, fresh and dry weight of root and shoot, root volume and root area was done one month after applying stress and Ti and SIIG indices were calculated based on these traits. After calculating the Ti index for the studied lines and obtaining the highest and lowest tolerance index for each trait, they were used to calculate the distance of each line from the positive ideal genotype (d +) and the ideal negative genotype (-d). In addition to using the SIIG index in this analysis, the grouping of the studied lines was done using cluster analysis using Ward method. This grouping was performed by applying the average of the lines for Ti index and the results of cluster analysis were compared with the results of the SIIG index. Statistical analysis of data was done using SPSS16 software and comparison of averages was done with Duncan's test at a probability level of 1%. Results and discussion The results of variance analysis of Ti showed that the lines had a significant difference in all traits at 1% probability level. Based on the results of the comparison of the average of durum wheat lines in terms of the Ti indices calculated from the traits, in most traits, the lines 9, 26, 34, 40 and 53 the lines had the highest value of Ti index and the lines 22, 29, 51, 77 and 79 were the lines with the lowest value of Ti index. The high level of this index on each line indicates the high tolerance of these lines to osmotic stress. The results of line rating using SIIG method showed that lines 9, 16, 24, 25, 26, 34, 35, 38, 53 and 64 had the highest SIIG in comparison with other lines and these lines were identified as the most tolerated ones to osmotic stress. Lines 22, 29, 30, 51, 52, 61, 73, 77, 79 and 82 were ten lines with the least amount of SIIG and were the most sensitive lines to osmotic stress. Conclusion Based on the indices of Ti, lines 34, 9, 53, 26, 40, 16, 64, 7 have a high average and lines 29, 77, 22, 30, 51, 13, 79 have the low average of the traits . According to the SIIG index, the lines 34.9, 53, 26, 16, 64, 38, 25, 35, 24 were in the high average group and the lines 61, 52, 51, 30, 82, 73, 79, 77, 29, 22 were in the low average group. These results were also obtained in cluster analysis, and the results of this grouping were highly consistent with the results of the lines' ranking using the SIIG index. This shows that the SIIG index helps the researcher to sum up the results of different indices. In general, it can be presented that in this study, the lines 9, 34, 53, 26, 16, 64, 38, 25, 35, 24 were tolerant lines and the lines 61, 52, 51, 30, 82, 73, 79, 77, 29, 22 were susceptible ones to osmotic stress.