Effect of source and sink limitation on yield and some agronomic characteristics in modern bread wheat cultivars under post anthesis water deficiency

In order to examine the effect of source and sink limitation and post anthesis water deficiency stress in determining of grain yield potential in nine modern bread wheat cultivars in the west of Iran with arid and semi-arid weather that is one of the main centers of crop diversity in the world, a split plot-factorial experiment based on randomized complete block design with three replications was used in crop year 2010-2011. Three treatments includes: control, flag leaf removal and removal of half of each spike was applied in the field research campus of agriculture and natural resources of Razi University. Water deficiency stress was started at anthesis and continued till physiological maturity (withholding of irrigation). Water deficiency caused significant reduction in the grain yield and the 1000 grain weight and caused significant increase in the number of fertile spikelets per spike. Flag leaf removal (source limitation) treatments showed that flag leaf contribution in grain yield production during grain filling in control and post-anthesis water deficiency stress condition were 10.1% and 13.4% respectively. In both conditions removal of spikelets spike-1 (sink limitation) treatment had higher significant effect on fertility of spikelets, grains spike-1, grain yield spike-1 and 1000 grain weight than flag leaf removal. Flag leaf removal treatment in some cultivars not only had no reduction effect on grain yield and 1000 grain weight but also increased them. These results may be due to an increase in photosynthesis rate of remaining leaves and/or increase in amount of carbohydrates remobilization that is stored in the stems. This phenomenon is called the compensatory effect. In both water regimes, there was a correlation between lower grain weight, no grains spike-1 and fertile spikelet spike-1 and lower yield potential of ‘Chamran’ cultivar. But, ‘Zarin’ and ‘Pishgam’ cultivars due to higher grain yield potential in post-anthesis under water deficiency stress and control, performed more studies, to advise farmers to cultivate them. There are probably better than any other cultivars that are common in these regions and sowing of them by farmers will be associated with less risk.