Phenotyping faba bean for drought adaptation

Faba bean (Vicia faba) is a promising protein crop for a green transition of our food and food production systems in temperate climates. The crop produces protein rich pulses, with nitrogen derived from the atmosphere, offering the potential to make crop production systems less reliant on fossil energy input. One challenge of increasing faba bean cropping is, however, their drought sensitivity induced yield instability, which may be specifically harmful during the indeterminate flowering period.

A faba bean phenotyping experiment was established at University of Copenhagen, combining field experiments with rhizotube observations. Five commercial cultivars were grown in field plots. To create drought conditions, the plots were partly covered by rain gutters to remove precipitation during the flowering period. In dry seasons, the well-watered control was irrigated. Aboveground growth parameters were assessed, root architectural traits were determined by a shovelomics approach, and stomata imprints were analysed for stomata size and density using a convolution neural network approach.

In order to obtain information on root growth dynamics, plants were grown in 2m tall rhizotubes with a diameter of 15cm and with a transparent surface. Root images were acquired to follow root development over time. Soil water sensors were installed, to observe water content and how it was affected by the drought treatment.

 

Results from the first two seasons of this three-year project show successful establishment of drought conditions in the field trial using the rain-gutter approach. Yield and yield composition were affected by drought treatment and showed a mean reduction of 0.7-0.8 T ha^-1. Cultivars show varying responses to the drought stress, which was reflected on root and shoot parameters. Stomata density and size showed genotypic variation, and cultivar specific plastic adaptation to drought. Stomata density and size correlated strongly with root traits observed from the shovelomics approach, indicating that a deeper, more proliferated root system can support larger transpiration demand. These findings were further supported by the rhiztobue experiments, where maximum rooting depth and stomata cover are correlated.

 

The preliminary results of this study show interesting interactions between shoot and root phenotyping at different scales, and expands our understanding of the water budget of faba bean.