Evaluation of water deficiency at the post anthesis and source limitation during grain filling on grain yield, yield formation, some morphological and phonological traits and gas exchange bread wheat cultivar

This paper attempts to determine the effect of post-anthesis water deficiency at the early and late grain growth periods separately and also the roles of main ear (spike) and leaves photosynthesis in yield production of wheat. The experiment was laid out in a randomized complete block design (RCBD) in a factorial arrangement with three replications. It comprised of source limitations i.e., control, defoliation of all leaves except the flag leaf and shaded ear and two water stress treatments i.e., well water or control (Irrigation in all stages of plant growth normally), water stress (post-anthesis water deficiency with withholding of irrigation). The results showed that the averages of grain yield and thousand grain weight of different treatments in controlled condition were 0.92 g spike-1 and 22.6 g respectively, while under water deficiency stress these values significantly reduced to 0.55 g spike-1 and 15.2 g respectively. Grain yield had the highest decrease percent under drought stress condition that it was probably due to reduce thousand grains weight under drought stress. The photosynthesis of all leaves except the flag leaf made significant contributions to the growing grains about 19% and ear photosynthesis makes a significant contribution to thousand grain weight of bread wheat, 18.6% in the absence of stress, and 23.3% under water deficit. Water deficiency at the post-anthesis significantly reduced net photosynthetic rate, stomatal conductance and transpiration rate. Net photosynthesis rate generally decreased with chlorophyll content and also this was paralleled by a lower stomatal conductance. Ear photosynthesis might represent a “buffer” to maintain grain yield under source limitations (e.g. defoliation, water stress conditions), and could have an important role even without stress, because an incipient ‘source’ limitation might be emerging in modern cultivars of bread wheat.