Effect of drought stress on vascular system in rachis of wheat (var.Rowshan Back Cross)

In order to study, the effect of drought stress on vascular system in wheat rachis (var.Rowshan Back Cross) this experiment was conducted in the research farm of Islamic Azad University of Saveh in 2009-2010 years in 4 replications. This experiment was arranged in randomized complete blocks design with drought stress factor in two levels including: 1- Control (without drought stress, 2- drought stress (from stem elongation stage to complete anthesis). The number, size and distribution of vascular bundle in different parts of spike were checked. The results have shown that, in both samples (control and drought stress), number and size of central vascular bundle acropetally decreased along the rachis from proximal to distal part of spike as the most decreasing number and size dedicated in central part. Samples under drought stress condition revealed that the number and size of vascular bundles decreased as compare to control and it was the result of drought stress. The size of vascular bundles decreased along the rachis in both the treatments as the biggest size of vascular bundles revealed in the middle of spike and then in the proximal and distal of spike respectively. There was a positive relation between the number and weight of grains with the number and size of vascular bundles for each spikelet along rachis of spike. The spikelets of middle part of spike rachis had the most average of weight and number of grains in both treatments as compare to other parts. However there are less weight and number of grains in the spike under drought stress in compare with the same parts in control situation. As the results revealed, the weight and the number of grains in drought stress conditions decreased because of decreasing in number and size of vascular bundles along the rachis of spike.