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Effect of Planting Date on Source Limitation of Genotypes of Wheat After Flowering

Physiologeal factors that control the growth of wheat grains are not well known. To evaluate the grain weight potentials and post-flowering source limitation, this study was carried out in climatical conditions of Neyriz in 1995 growing season. The design of the experiment was split plot with four repleations. The main plots included four planting dates (6th Nov., 22nd Nov., 7th Dec. and 22nd Dec.), and the sub plots included three wheat cultivars (Roshan, Falat and Ghods). Assimilate increase for grain growth was done through decreasing the number of spiklets. In each spike, four spikelets with numbers 3, 6, 9 and 12 were kept and others were left out. The results indicated that source limitation increased with delaying the planting practice, in such a manner that the grains produced in the delayed planting date faced with a limitation of about 44.2%; whereas the limitation for the first planting date was 4.8%. On the other hand, comparison among cultivars showed that source limitation average for Roshan cultivar was less than Falat and Ghods. The source limitations for above-mentioned cultivars were 13.6%, 20.6% and 22.9%, respectively.