The role of current photosynthesis on grain yield formation, some agronomic characteristics and germination traits in two bread wheat cultivars under terminal drought stress condition

A greenhouse and a laboratory experiments were conducted during 2011-2012 in the Razi University in Kermanshah state in the west of Iran to determine the effect of irrigation and source manipulation treatments on grain yield, its components and seed germination traits of two bread wheat cultivars. The irrigation treatments including Control (Non water stress) and water deficiency stress (from anthesis and continued until physiological maturity). The wheat cultivars including Marvdasht and DN-11 and the source manipulation treatments including control (C), defoliation of flag leaf (T1), defoliation of all leaves except the flag leaf (T2), de-awning (T3) and ear shaded (T4), were imposed at anthesis. Seeds of the greenhouse experiment were used for the laboratory experiment. In the laboratory experiment, germination traits of seed produced from maternal plant under irrigation and source manipulation treatments were tested. Results showed that irrigation treatments had a significant effect on grain yield, agronomic characteristics and some germination traits. The most variation percentage of yield, biomass, harvest index and 1000 grain weight under drought stress compared to well water were measured for Marvdasht cultivar. These results showed that Marvdasht cultivar was more sensitive to applying of water deficiency at grain filling stage. Water deficiency caused less reduction in grain yield of DN-11 cultivar. Removing of photosynthetic sources of assimilates reduced grain yield via grain weight and number of grains per spike reduction. In this case the role of spike photosynthesis in grain filling (35.4%) was higher than the flag leaf (21.6%) and lower leaves (17.7%). Awns had the lowest role in grain filling (7.7%). The results of analysis of variance showed that water stress significantly affected seedling dry weight, seed germination percentage and mean germination time. But, there was no significant difference among irrigation treatments in terms of seedling length, plumule to radicle ratio and seed vigor index. Removal of ear photosynthesis had the lowest seed germination percentage and seedling growth parameters, but had the highest mean germination time.

Wheat, Drought stress, Grain yield, Defoliation, Spike, Awn, Germination, Mean germination time, Seedling