Effect of Source Restriction on the Grain Yield and yield components inIranian Wheat cultivars

Studies manipulating the source-sink relationships during post anthesis in wheat have shown inconsistent results, concluding that wheat yield could be either sinkor source-limited. The aim of this study was to determine source limitation degree of broad range of Iranian wheat cultivars. Field experiments were conducted at the Tehran University research farm during 2010- 2011 growing seasons.A split plot design based on RCBD was carried with 3 replications. Treatment included 36 wheat cultivars and different levels of defoliation (non-defoliated control(ND), removal of all leaves (FD), removal of all leaves except the flag leaf (PD)). The plants were defoliated at flowering and 15 day after flowering growth stages. A wide range of responses to defoliation treatments observed among the cultivars. Removal of all leaves except the flag leaf in flowering stage caused reduction of yield main spike, Grain number per spike and thousand weights by 10.71%, 8.98% and 12.26%, respectively. Similarly removal of all leaves caused reduction of yield main spike, Grain number per spike and thousand weights by 24.70%, 19.58% and 20.00%, respectively. Removal of all leaves except the flag leaf in 15 day after flowering stage caused reduction of yield main spike, Grain number per spike and thousand weights by 9.14%, 7.24%, 1.42%, respectively. Similarly removal of all leaves caused reduction of yield main spike, Grain number per spike and thousand weights by 22.20%, 17.40% and 6.27%, respectively. In general, removal of all leaves had larger decreasing effects than that of flag leaf alone.