UC San Diego

Drought is a major stress which reduces crop yields, and which will continue to be an increasing problem in the coming years as climate change and limited fresh water supplies lead to higher temperatures, desertification, and increased soil salinity. These environmental stresses can significantly impact both the seed yield and quality of crops. There are several strategies which plants utilize to mitigate the effects of water deficit, making the identification of specific traits which convey drought tolerance difficult. As drought tolerance is a complex trait, accurate phenotyping to select for resilient genotypes is needed to improve our understanding of plant drought responses.

In this study, stable carbon isotope screening (δ13C) of a diversity set of the crop plant Brassica napus grown in the field was used to identify accessions with traits linked with extremes in water use efficiency (WUE). We investigated physiological characteristics of the selected accessions to identify how these characteristics translate to differences in WUE. Using gas exchange techniques, we identified an interesting spring-type accession (G302, Mozart), which exhibited the highest WUE in the field, based on δ13C measurements. This line displayed high CO2 assimilation rates coupled with an increased electron transport capacity (Jmax) under lab conditions. We also analyzed stomatal conductance response to exogenous abscisic acid (ABA) in the selected accessions. While little variation was observed in the response rates of spring-type accessions, one semi-winter accession demonstrated a significantly more rapid response to exogenous ABA, which was in line with a higher WUE derived from δ13C measurements. This research supports the genetic data showing distinct genetic lineages for spring and semi-winter accessions. It also illustrates the importance of examining natural variation at a physiological level for understanding the underlying mechanisms of drought responses.