Wheat, as a main crop, plays a significant role in supplying food and human health. However, water stress and zinc deficiency are important factors limiting the growth and yield of crop plants including wheat. On the other hand, roots are important not only for providing water, nutrients and hormones but also for their contribution to water stress tolerance and nutrient use efficiency. Therefore, this study was conducted in order to investigate the roles of root morphological characteristics and also foliar application of zinc sulphate on the responses of wheat cultivars to water deficit. In this experiment, four wheat cultivars (Ghods, Roshan, Chamran and Kavir) were evaluated under four levels of irrigation (irrigation based on 100, 90, 75 and 50% of crop water requirement) and two levels of zinc (foliar application of zinc sulphate at stem elongation stage and non-sprayed as control). The experiment was carried out at Isfahan University of technology, arranged as factorial in a completely randomized design with three replications. Wheat plants were harvested at physiological maturity. Measured traits were SPAD index, plant height, tiller numbers, spike numbers, grain weight per plant and shoot dry weight and also root parameters including root dry weight, volume, cumulative surface and length and diameter, determined at 0-30, 30-60 and 60-100 cm soil depths. The results showed that there were significant differences among cultivars for all measured traits, except plant height and SPAD index. Tiller numbers, spike numbers, grain weight per plant and shoot dry weight were decreased as the available water was reduced in soil. However, the responses of plant height and SPAD index to water deficit were dependent on cultivar, irrigation and zinc level. Root dry weight was decreased under mild and severe levels of water deficit (it was instead increased with zinc foliar application under mild water deficit in cultivars Ghods and Roshan and under severe water deficit in Ghods). The extent of decreases in root dry weight was greater for the roots measured at 30-60 cm soil depth. The responses of other root parameters including root volume, cumulative root surface and length and root diameter to water stress were dependent on both experimental treatments and the soil depth at which roots were measured. The root system of Ghods, and Chamran cultivars showed more flexibility in response to water deficit as compared to those of Kavir and Roshan. Foliar spray of zinc sulphate, in average, increased grain yield (grain weight per plant) 12.3 percent. However, the extent of the increases was higher under irrigation based on 100 (24.6 percent), than under irrigation based on 90, 75 and 55% (3.75, 10.79 and 8.33 percent, respectively) of crop water requirement. The increase in grain yield was significant only in Ghods (28.6), showing that this cultivar was more responsive to zinc application than others. The effects of foliar application of zinc sulphate on cumulative root surface and length were more evident in roots measured at 0-30 cm and on root dry weight and root volume at 30-60 cm soil depth. Root depth was not significantly affected by zinc application. Chamran was the most responsive cultivar (in most cases positively) in terms of the changes in root parameters under zinc foliar application, instead, zinc application generally restrained root growth of Ghods, Roshan and Kavir. Under all irrigation levels and in most cases, there were significant negative correlations between grain yield and the changes in root characteristics. At soil depth of 0-30 cm, the negative correlation between grain yield and root dry weight became higher with increasing water stress. The results from this experiment showed that the effect of zinc foliar application on wheat root growth pattern was dependent not only on irrigation level and cultivar but also on the soil depth at which root parameters were measured. Keywords: Genetic variation, Foliar application, Root parameters, Soil layers, Water-deficit stress, Wheat, Zinc sulfate.