Re-translocation of stem and spike reserves was investigated in source:sink restricted wheat subjected to water and nitrogen deficiency during seed filling. Either sink or source restriction significantly decreased the amount of current photosynthesis and its contribution to grain yield. Furthermore, source limitation increased stem and spike reserves contribution to seed filling process. Higher amount of stem reserve mobilization in source restricted vs. control and sink restricted plants indicates that at rapid grain filling stage (14 days after anthesis to physiological maturity), stem dry matter decreases to provide assimilates for kernel after defoliation. In spike halved plants, drought stress significantly decreased grain yield, indicating that when the sink is restricted, postanthesis drought stress can increase sink limitation through lower grain filling rate and dry matter allocation to grain two weeks after anthesis at the beginning of rapid grain filling stage. On the other hand, in spike halved plants, more nitrogen supply at anthesis increased grain yield because more dry matter allocation to grain is not associated with more current photosynthesis. But when all the leaves were removed except flag leaf, more postanthesis nitrogen could not increase dry matter allocation to grain filling process, showing that postanthesis nitrogen supply increases grain yield by decreasing sink limitation, and not by increasing source strength.
current photosynthesis; dry matter allocation; grain filling rate; stem reserves; wheat (Triticnm aestivum L.)
