One major challenge to the success of hybrid wheat is the low outcrossing rates of the maternal parent, partly due to the short functional life span of the floral stigma. Despite their importance in seed production, the post-anthesis viability of unpollinated stigmas has been overlooked. Thus, research to understand the dynamics of stigma survival in wheat could be key to improving the efficiency of hybrid seed production.

To first address this, we have developed a phenotyping approach for the quantification of female floral traits of field-grown plants by combining light microscopy and machine learning. The application of this approach reveals (1) the presence of distinct stigma growth patterns among cultivars; (2) this trait to be robust across different environments and; (3) the existence of a common underlying developmental programme. Secondly, we examined the seed set capacity of a subset of six male sterile (MS) cultivars, each varying in the onset of stigma deterioration.

To mimic a hybrid seed production scenario, MS cultivars were grown during two consecutive field seasons, and open pollination was allowed up to 15 days after flowering of the female parent. Detailed analysis of the temporal and spatial distribution of hybrid seed set along the MS spike showed that grain production remained remarkably stable during the pollination window tested.

Contrary to previous assumptions within the hybrid wheat community, our findings challenge the notion that stigma longevity poses a significant limitation to hybrid wheat seed production.

We, therefore, conclude that breeding efforts should prioritise the study of other female traits, such as enhanced access to airborne pollen.