The influence of exogenously applied “anti-stress” agents in the upregulation of the drought response in Iraqi wheat varieties
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Bread wheat (Triticum aestivum L.) is one of the most important cereal crops grown in the world. It has great importance because it constitutes a major source of carbohydrate for more than one third of the world’s population (Budak et al., 2013). In the last three decades, drought conditions are becoming more widespread in wheat production areas including Europe, Australia and Asia, and it is considered a major cause of reduced wheat growth and productivity in most developing countries with semi-arid climates. Drought constitutes the most important threat for wheat production in Iraq and especially for the Kurdistan Regional Governate owing to the limited source of water during at least some part of the growing period. Because wheat is considered a staple food and has economic importance for the Kurdistan Regional Government research is needed to determine the production capacity of Iraqi wheat varieties under drought stress and the potential for the maximization of the drought tolerance response. The soil moisture holding capacity of the intended growing medium was measured gravimetrically in pots with and without wheat plants and correlated with the soil capacitance measured using a TDR Theta Probe (Delta-T Devices). This was used to determine the available water content of the soil (AWC) and to control and manage the watering regimes during drought studies. The results of a study of the response of different cultivars of Iraqi wheat (Triticum aestivum L.) to watering regimes of 70% and 50% showed that drought stress had a significant effect on the biomass and yield traits especially tiller number and stem bundle weight compared to normal conditions. The highest significant difference was observed for cv. Tamooz 2 in comparison to Adana 99, but there was a little difference between cvs. Rizgary and Sham 6. The effect of the exogenous application of salicylic acid (SA) and molybdenum (Mo) on drought tolerance of cvs. Tamooz 2 and Adana 99, showed that Tamooz 2 had higher values for growth characteristics and higher yield potential when sprayed with a lower concentration of SA (1.44 mM) under well-watered conditions in comparison with Adana 99. The effect of spraying variety Tamooz 2 with SA at different growth stages indicated that biomass production and yield components (the number of spikes/pot, grain dry weight and average 1000 grain dry weight) significantly increased at both stem+flower as well as leaf+stem+flower sprayings for plants subjected to drought. Also, SA treatments at stem extension and flowering had a positive effect on the up-regulation of the drought response gene CBF/DREB under drought stress conditions. These findings indicate that agronomic treatments with exogenous applications of salicylic acid and molybdenum could help to reduce the effects of drought in the field.