Physiological Constraints in Improvement of Grain Size and Grain Filling in Wheat.

To understand physiological constraints in grain weight improvement, the synthetic components and the seed water relations were studied at different maturity intervals in three wheat genotypes widely differing in their grain size. The synthetic components like sugar, protein and ash which are also osmotically active were significantly higher in large grain types (IWP5308 and Sel-111) and this caused higher inflow of water into the seed and resulted in enlargement of seed coat/structural component. The rate of post-anthesis flag leaf photosynthesis reduced drastically in IWP 5308 and explained to a large extent its lower grain density. The study showed that the rate of post-anthesis flag leaf photosynthesis and water relation parameters of the developing grain could largely explain the constraints in realisation of potential synthetic and storage capacity of the wheat genotypes with improved structural components.