Response of seed germination and seedling growth of (Triticum aestivum and Triticum durum L.) wheat genotypes to salinity stress and temperature regimes

Introduction Wheat has been planted in saline conditions in many areas of central and southern Khuzestan, and high temperatures at early planting date may exacerbate the effects of salinity. Investigations show that not only different crop species but also genotypes of a species may have a different tolerance to salinity. Main constructs of tolerant wheat cultivars include the separation of sodium and chlorine in vacuole root and leaf cells. It has also been reported that tolerance cultivars, with osmotic stress in the root environment, have better seedling growth rates. The reason for the difference between the wheat cultivars studied in response to salinity was the ratio of sodium to potassium in the seedling of these cultivars. Seedling tolerant to salinity in wheat has a lower sodium content and higher potassium content than sensitive genotypes.  Materials and Methods  In order to investigate the effect of salinity and temperature on germination and seedling growth of three genotypes of bread and durum wheat, this experiment was carried out in the laboratory of Islamic Azad University, Khouzestan Research Branch, in 2011 in Petri Dish growing conditions. Factorial experiment was carried out using three temperature treatments (15/10, 25/20 and 35/30 ° C night/ day), wheat genotypes (two bread genotypes of Chamran and 20 Sarasary and Durum Line D85-17) and salinity (0, 2, 4, 8, and 12 ds/m). During the experiment, the germinated seed was considered to have a root length of at least two millimeters. One week after the treatments, from each petri dish, five seeds were selected to measure the traits. The traits of root length, stem and coleoptile, germination percentage, germination rate and sodium / potassium ratio were measured.   Results and discussion The results showed that salinity increased germination percentage significantly in wheat genotypes. The maximum and minimum stem length was 25.25 and 35.30 ° C, respectively. With increasing temperature from 15.10 to 25.20 ° C, there was 43% increase in stem length. The increase in temperature from 25.20 ° C to 35.30 ° C reduced the stem length by about 52%. The percentage reduction in the root length of bread wheat cultivars, Chamran, as well as the durum line in 12 ds.m-1 compared to control distilled water were 41.5, 41.1 and 59.5%, respectively. Wheat genotypes at 25/25 ° C had the highest seedling growth. The highest and lowest germination percentages were observed at 15/15 and 35/30 ° C temperature treatments. Line 17-85D in comparison with bread genotypes was more sensitive to salinity and temperature. Increasing ambient temperature exacerbated the effect of salinity on germination and seedling growth. Increasing temperature increased the effect of salinity on plumule length, so that the reduction in plumule length under salinity of 12 dS/m and 15/35, 25/20 and 35/30° C temperature treatments, was 33.3, 50 and 84 percent respectively. Na+/K+ ratio was higher in wheat genotypes at high temperatures. Durum line D85-17 had a higher Na+/K+ and sensitivity to salinity compared to two bread genotypes.     Conclusions According to the results, sodium and potassium ratio index was a suitable criterion for evaluating reaction of genotypes to salinity in temperature treatments. The Durum line was more susceptible to salinity and two bread genotypes were more tolerant to salinity due to less sodium accumulation and a higher sodium to potassium ratio. Meanwhile, genotypes such as Chamran, with more tolerance to the temperature, had less susceptibility to salinity. In general, it was recommended that in order to increase the accuracy of the research, the response of other wheat genotypes to salinity and temperature should be studied.