In order to study the effect of water deficit on root morphological treat of sesame, a three replicated split plot experiment was conducted based on randomized complete block design during 2008- 2009 growing season in Agriculture and Natural Resources Research Center in Parsabad, Ardabil province. In this experiment, irrigation as the main factor with three levels (100 (field capacity), 75 and 50 percent of plant water requirement) and ten sesame cultivars as the secondary factor were included. To calculate the water requirement of the sesame, the CROPWAT software (Penman- Monteith method) was used according to FAO-56. Results showed that difference between cultivars and irrigation regimes in respect to root treat was significant at root characters. Also, interaction between cultivars and irrigation regimes were significant in all traits. Comparing of means showed that under water deficit condition, all root treats (diameter, volume and surface, wet and dry mater), were reduced. In this study difference among cultivars in respect to root system was considerable and should be considered in drought résistance breeding programs. Grouping of cultivars showed that the Karaj1, and Ultan cultivars with suitable root system, were tolerant cultivars against water deficit. The Indian14 and Yellowhite cultivars had weaker root system. Generations which are derived from crossing between tolerant and susceptible cultivars could be used as segregating population in genetic and molecular studies.
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