Abstract
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) (I1), at booting stage (43 of the Zadoks) ( I2), at initiation of grain – filling stage (70 of the Zadoks) (I3), and full irrigation (I4). Subplots included three cultivars, that is, Chamran (C1), Marvdasht (C2), and Shahriar (C3). Compared to control treatment (I4), treatments (I1), (I2) and (I3) exhibited 85, 57 and 43% yield decreases, respectively. In response to moisture stress during different growth stages, Shahriar CV (C3) was damaged more severely than Chamran CV (C1), 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. Key words: Bread wheat, cultivar, drought stress, path analysis, grain yield, yield components.
Highlights
Drought is the most common environmental stress affectting about 32% of 99 million hectares under wheat cultivation in developing countries and at least 60 million hectares under wheat cultivation in developed countries (Rajaram, 2000)
Main plots included four drought stress treatments, that is, (I1): drought imposed from onset of stem elongation stage (31 of the Zadoks) until maturity; (I2) : drought imposed from onset of boot stage (43 of the Zadoks), (I3) : drought imposed from onset of grainfilling stage (70 of the Zadoks); and (I4): full irrigation
Mean temperature was higher in Mahidasht region during terminate months of wheat growth period (May and June) compared to Sararood region, which resulted in shortening the reproductive period, in reducing wheat yield in this region (Figures 1 and 2)
Summary
Drought is the most common environmental stress affectting about 32% of 99 million hectares under wheat cultivation in developing countries and at least 60 million hectares under wheat cultivation in developed countries (Rajaram, 2000). In Iran, about 67% of wheat – cultured area is devoted to dryfarming lands, which are exposed to drought stress during growth season (Galeshi and Oskuei, 2001). Such limiting factors as low temperature in winter (absolute minimum of temperature;-30°C), high temperature during the terminal grain filling period (+35°C), and post anthesis water deficit condition in irrigated wheat, influence crop growth and yield (Sanjari, 2001). The drought stress entailed a significant decrease in grain yield, number of fertile spikes per unit area, number of grains per spike, 1000 grain weight, biological yield, harvest index and plant height (Fischer, 1979; Debaek et al.,1996; Moustafa et al, 1996; Reynolds et al, 2001)
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