Evaluating the effect of water deficit and source limitation on grain yield and remobilization of dry matter at post anthesis in bread wheat cultivars

Among different cereal crops, wheat has the most cultivation areas and yield in the world. Also, wheat is the major crops grown in arid and semi-arid regions. The occurrence of drought stress during grain filling is the prominent and inevitable characteristic of these areas. The objectives of this research were to determine the effect of water deficiency and the role of current and storage sources of assimilates on grain filling, grain yield and carbohydrates remobilization. Therefore, an experiment was carried out in a split-plot factorial arranged in a randomized complete block design with three replications during 2010-2011 cropping season at the Research Farm of Razi University in Iran. The main factor was the irrigation treatments including control or non-stressed treatment (irrigating plants at all growing stages based on crop water requirement and climatic conditions) and water deficit stress (irrigation cessation after anthesis). The combination of eight wheat cultivars including Bahar, Parsi, Pishtaz, Pishgam, Chamran, Zarin, Sivand, Marvdasht and one line DN-11 along with the photosynthetic sources limiting treatments including control (no limitation of photosynthetic sources), defoliation of the flag leaf, defoliation of all leaves except the flag leaf), de-awning and shading over the ear were considered as the sub plots. The results showed that post-anthesis water deficiency significantly decreased grain yield (22.2%) and removal of photosynthetic sources reduced grain yield through reducing the grain weight. In this case the role of spike photosynthesis in grain filling (35.4%) was greater than the flag leaf and lower leaves roles (18.6 and 18.5%, respectively) and awns had the lowest role in grain filling (3.3%). Under removing of assimilate sources, remobilization of stored material from the different parts of stem internodes was increased, suggesting the compensatory role of them in yield loss prevention. Water deficit stress could not increase the remobilization efficiency, but in terms of mentioned traits, there were differences amongst cultivars and different removing photosynthetic sources. In both control and water deficiency stresses treatments, the amounts of remobilization from different parts of stem and spike to the growing grains were similar. Under well water condition, the grain yield increased due to higher photosynthesis rate compared to water deficiency stress conditions.