Study of effects of drought stress on yield and yield components of four sunflower cultivars in Zanjan, Iran

To study the production efficiency of four sunflower cultivars and hybrids introduced for cold regions under different moisture stress levels, a split-plot experiment was carried out on the basis of Randomized Complete Block Design with three replications in experimental field of Agriculture and Natural Resources Research Center, Zanjan, Iran in 2009. The stress treatment included four levels (no-water stress, stress at head formation stage, stress at flowering stage and stress at grain filling period) and the cultivars included Master and Lakomka and two hybrids Euroflour and Azargol. At harvest, the traits which were measured included head size/plant, grain number/head, growth period duration, 1000-grain weight, biological yield, harvest index and grain yield. The data were statistically analyzed and the means were compared by Duncan's multiple range test (DMRT) at 5% level when the effects of treatments were significant. For this comparison, the software MSTATC and MS-Excel were used. The results showed that Azargol had the highest yield under no-stress conditions and Master had the lowest yield under stress at head formation stage. Azargol had higher yield under both stress and no-stress conditions than the other cultivars. Also, the stress from head formation until the end of growing season had the highest effect on yield components, especially 1000-grain weight and head diameter because the plants were exposed to drought stress for a longer time. Head diameter is one of the essential traits which is decreased by moisture stress and adversely affects yield components such as grain number/head. No-stress treatment had the greatest head diameter whereas the stress at head formation stage had the lowest head diameter. No-stress condition and Lakomka had the highest 1000-grain weight (78.85 and 80.24 g, respectively) while the stress at head formation stage and Euroflour had the lowest one (64.03 and 64.4 g, respectively). In the case of grain number/head, the differences among different moisture stress levels and the interactions between stress and cultivar were not significant, but the cultivars affected this trait at 1% level, so that Azargol and Euroflour had the highest grain number and Master and Lakomka had the lowest one. The results indicated that drought stress severely affected biological yield and decreased it, so that the longer the duration of stress was, the shorter the growth period, the lower the photosynthesizing area and hence, the lower the yield were.