Precise Evaluation of Transpiration Patterns in Relation to Grain Yield Under Drought Stress in Faba Bean

Faba bean (<i>Vicia faba</i> L.) is a key crop for sustainable agriculture in temperate cropping systems due to its nitrogen-fixing ability and high protein content, but its productivity is increasingly threatened by drought stress driven by climate change. Precise phenotyping under semicontrolled conditions is crucial for understanding drought responses. High-throughput precision phenotyping enables efficient evaluation of many genotypes, revealing detailed water-use patterns as a basis for breeding productive, drought-resilient cultivars. In this study, faba bean genotypes were grown in a precision phenotyping facility comprising 120-L containers filled with mineral soil to simulate field-like growth conditions. Each container was placed on a high-precision gravimetric scale to record water use in real time in relation to 3-D spectral image information. Precise measurement of genotype-specific transpiration behavior using gravimetric methods enabled detailed insights into the transpiration patterns of different genotypes in response to ambient temperature and humidity fluctuations throughout the day and night, and across the whole-life cycle. The results showed that total water use, water-use efficiency, and consequently yield were particularly influenced by specific transpiration parameters, such as the maximum transpiration rate and the vapor pressure deficit threshold at which stomatal conductance was declined. The results revealed genetically determined variation for transpiration responses to drought stress. Genotypes that reduced water loss earlier tended to achieve higher grain yields and use water more efficiently. The findings show that precise automated phenotyping can identify previously undiscovered genetic variation for breeding drought-tolerant faba bean varieties, which are crucial for ensuring productivity under increasingly water-limited conditions.