Influence of shading during different periods upon ear development, grain yield and its components in two wheat cultivars

The influence of shading during different phenological crop phases upon ear development, dry matter accumu- lation and distribution, yield and its components was studied in two wheat cultivars.Results showed that achie- ving a large potential spikelet number during the early growth stages is very important, due to the natural reduction that occurs after the terminal spikelet is formed.Spikelet number was determined by the length of the period to reach the doubleridge stage and by the average spikelet production rate and duration, which differed between cultivars.Shading did not decrease maximum spikelet number in the tall standard cultivar Klein Toledo, which was better buffered against environmental conditions.Maximum floret number was not modi- fied by shading and was very stable in both cultivars, at least in the central portion of the ear.The same reduc- tion in potential grain sites after maximum floret number was achieved in both cultivars, showing the great influence that the earlier crop phases exert upon grain yield.Potential spikelet number per ear and grain number per spikelet appeared to be the most important yield com- ponents, due to their influence upon grain number per ear and hence grain per m 2 of soil surface, which was the main yield determinant.