The potential of leaf water relation traits for drought tolerance phenotyping in commercial Eucalyptus genotypes

Although leaf turgor loss point reflects osmotic potential variation in Eucalyptus, the osmometer method alone does not reliably rank drought tolerance among genotypes in breeding-oriented common-garden trials.

Increasing droughts driven by climate change highlight the need to identify traits associated with drought tolerance in tree breeding programs. However, finding operationalizable traits that effectively distinguish drought tolerance among genotypes of the same species remains challenging. Here, we assessed 21 commercial Eucalyptus genotypes grown in a common garden in southern Brazil to evaluate the potential of leaf water relation traits for drought tolerance phenotyping. These traits were derived from pressure-volume curves. We also tested the utility of the osmometer method as a rapid estimator of the leaf water potential at turgor loss (Ψ_tlp), using osmotic potential at full hydration (π₀). Among all leaf traits studied, only Ψ_tlp and π₀ showed some association with expected drought tolerance. Both traits exhibited significant seasonal plasticity, but were unrelated to a field-based with drought tolerance index. Variation in Ψ_tlp across genotypes was limited, likely due to prior selection forproductivity, which may have narrowed trait variability. Although Ψ_tlp was strongly influenced by π0, the osmometer method failed to reliably rank genotypes by drought tolerance. Our findings indicate that, while leaf water relation traits—particularly Ψ_tlp and π₀—have some potential for phenotyping, their current application in fast, operational screening for drought tolerance in Eucalyptus breeding programs remains limited. Further research is needed to validate and improve the practical use of these traits and methods.