Evaluation of physiological traits, yield and yield components at two growth stages in 10 durum wheat lines grown under rainfed conditions in Southern Syria

Water stress, which limits the distribution and productivity of durum wheat (Triticum durum Desf.) in the Mediterranean region, is also considered to be a major factor reducing yield in semiarid regions. Improving drought resistance is thus an important objective in plant breeding programs for rainfed agriculture. The current study was carried out to identify drought-tolerant durum wheat lines among 10 lines and one variety (Douma1, the control) in the first and second settlement zones in the Southern part of Syria and to recognize the most important physiological parameters associated with drought tolerance. Membrane stability index, chlorophyll (chl) content, relative water content and chl fluorescence were recorded at the vegetative and anthesis stages, as were yield and yield components. Data recorded at vegetative and anthesis stages in both zones showed that there were significant differences between all lines growing in the first and second settlement zones and that all characters in the second zone were significantly lower than those in the first zone. Line 1 was superior to Douma1 in terms of membrane stability index, relative water content, chl content and chl florescence, also showing better yield and higher total plant biomass, tiller number/m2, 1000 grain weight and grain number/ear than the control. The ability of wheat cultivars to perform reasonably well in variable rainfall and water-stressed environments is an important trait since it allows for stable production under drought stress. Moreover, prior to genetic manipulation, it is important to characterize the physiological parameters of known drought-tolerant or drought-sensitive wheat cultivars with the objective of better understanding their physiological responses under drought

Response to temperature stress of reactive oxygen species scavenging enzymes in the cross-tolerance of barley seed germination*

A number of studies have shown the existence of cross-tolerance in plants, but the physiological mechanism is poorly understood. In this study, we used the germination of barley seeds as a system to investigate the cross-tolerance of low-temperature pretreatment to high-temperature stress and the possible involvement of reactive oxygen species (ROS) scavenging enzymes in the cross-tolerance. After pretreatment at 0 °C for different periods of time, barley seeds were germinated at 35 °C, and the content of malondialdehyde (MDA) and the activities of ROS scavenging enzymes were measured by a spectrophotometer analysis. The results showed that barley seed germinated very poorly at 35 °C, and this inhibitive effect could be overcome by pretreatment at 0 °C. The MDA content varied, depending on the temperature at which seeds germinated, while barley seeds pretreated at 0 °C did not change the MDA content. Compared with seeds germinated directly at 35 °C, the seeds pretreated first at 0 °C and then germinated at 35 °C had markedly increased activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT), and glutathione reductase (GR). The SOD and APX activities of seeds germinated at 35 °C after 0 °C-pretreatment were even substantially higher than those at 25 °C, and GR activity was similar to that at 25 °C, at which the highest germination performance of barley seeds was achieved. These results indicate that low-temperature pretreatment can markedly increase the tolerance of barley seed to high temperature during germination, this being related to the increase in ROS scavenging enzyme activity. This may provide a new method for increasing seed germination under stress environments, and may be an excellent model system for the study of cross-tolerance