Improving and Stabilizing Harvest Index in Wheat Across Environments.

As grain growth is still more sink- than source-limited, further gains in yield would require improvements in grain number. This would become even more important if improvements in photosynthesis are finally achieved. In the past, this has been achieved by increases in spike weight at anthesis. In the future this might be by increasing fruiting efficiency (FE, the efficiency with which dry matter allocated to the spikes during pre-anthesis is used to determine grain number). FE might be increased through improving fertility of floret primordia by reducing mortality. Within high-yielding lines differences in yield were associated to differences in FE. But the actual benefits can only be achieved if it does not bring about parallel reductions in the potential size of the grains. Therefore, increases in FE based on decreasing the requirements of floret primordia to become fertile florets should be avoided.

As it would be extremely difficult to determine FE in a realistic breeding program, advances in breeding through this trait would largely depend upon identifying genetic bases controlling it and then manipulating these bases through direct selection for the trait. As a proof of concept, an experimental divergent selection for a (non-destructive) surrogate of FE was implemented ending up with lines consistently producing more and less grains than the controls. Currently we have an EU-project (ADAPTAWHEAT) in which -among several other things- we expect to identify genetic bases for fruiting efficiency and its major developmental determinants. In this presentation we will describe advances in this project towards this particular aim.