Differential agronomic responses of bread wheat cultivars to drought stress in the west of Iran

Two similar and concurrent experiments were carried out in 2007-2008 on dry land agriculture research sub-institute Sararood and Mahidasht agricultural research center to study the effects of drought stress on yield and yield components of wheat cultivars under field conditions. The experimental design was split plot based on randomized complete block design with three replications. Main plots consisted of four drought stress treatments which was imposed by irrigation stoppage at different growth stages, that is, at initiation of stem elongation stage (31 of the Zadoks) (I(1)), at booting stage (43 of the Zadoks) (I(2)), at initiation of grain - filling stage (70 of the Zadoks) (I(3)), and full irrigation (I(4)). Subplots included three cultivars, that is, Chamran (C(1)), Marvdasht (C(2)), and Shahriar (C(3)). Compared to control treatment (I(4)), treatments (I(1)), (I(2)) and (I(3)) exhibited 85, 57 and 43% yield decreases, respectively. In response to moisture stress during different growth stages, Shahriar CV (C(3)) was damaged more severely than Chamran CV (C(1)), the latter enjoyed more yield stability under such conditions. The result of stepwise regression analysis showed that the most important yield component was number of grains per spike followed by number of spikes per unit area, then, by 1000 grain weight. Analysis of simple correlation and path analysis showed that, in overall, given direct and indirect effects of yield components on grain yields, number of grain per spike had the largest effect on grain yield.