Document Type : Original Article
Authors
1 Faculty of Agriculture, Islamic Azad University, Karaj
2 University of Birjand
3 Islamic Azad University, Shahre-Rey, Iran
4 Islamic Azad University, Varamin
Abstract
In order to evaluate effects of drought stress on yield and yield components of two wheat cultivars under field condition, two similar experiments were conducted in 2004 in Field Research Stations of Islamic Azad Universities of Karaj and Torbat-e-Jam Unites. The study was arranged as factorial experiments based on a randomized complete block design with four replications. The first factor was consisted of nine different irrigation regimes including control (T1), irrigating when 60 and 80 percent of soil moisture was depleted at stem elongation to ripening stage (T2 and T3, respectively), at the start of flowering to ripening (T5 and T7, respectively), at flowering stage (T4 and T6, respectively), and irrigation termination at flowering and grain filling stages to ripening stage (T8 and T9, respectively). The second factor was included two wheat cultivars, Chamran and Marvdasht. Results showed a significant difference between different treatments of drought stress and control regarding yield and yield components. Irrigation termination from flowering onward led to the lowest grain yield, with 64 percent reduction compared to control. The lowest yield reduction equal to 19 percent beside control was obtained with irrigating at 60 percent soil moisture depletion from stem elongation up to end of growth period. According to these results, the most sensitive growth stages of wheat to drought stress were flowering and grain filling stages. Marvdasht despite its higher yield under sufficient moisture condition, and even under water-deficit through growth period, suffered more damage than Chamran from terminal irrigation termination. Under optimum condition of humidity, grains per spike and length of peduncle showed higher correlation with grain yield, respectively. When irrigation was withheld from flowering to ripening stage, weight of 1000 kernels showed a positive and significant correlation with yield, indicating that impact of water stress in this stage on yield was mediated by reduction of kernel weight.
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