Many studies investigating genetic variation in transpiration responses to evaporative demand had relied on vapor pressure deficit (VPD) as the sole driver, often under controlled conditions. However, scaling such approaches to large genetic studies remained challenging. As an alternative measure of evaporative demand, this study proposed the use of reference evapotranspiration (ETref), which incorporated light as a key driver. This approach enabled large-scale phenotyping for genetic studies in outdoor environments that more closely represented field conditions.
Five experiments were conducted across three outdoor phenotyping platforms—a high-throughput, a low-throughput, and a lysimetric platform—using large panels of sorghum and pearl millet inbred lines. Protocols were developed and adapted to each platform to quantify transpiration responses to ETref, along with additional platform-specific traits.
Transpiration responses were best described by linear models, and all measured traits exhibited significant genetic variation and heritability in both crops, supporting their use in genetic analyses. Correlations within and across experiments highlighted the influence of soil conditions as well as species-specific differences.
Overall, the study demonstrated that these platforms were well suited for capturing genetic variation in transpiration responses to ETref and highlighted the potential of the low-throughput platform as a reliable and cost-effective tool for phenotyping this key drought-adaptive trait in breeding programs.
