A high-throughput approach for quantifying turgor loss point in grapevine

Quantifying drought tolerance in crops is critical for agriculture management under environmental change, and drought response traits in grape vine have long been the focus of viticultural research. Turgor loss point (π_tlp) is gaining attention as an indicator of drought tolerance in plants, though estimating π_tlp often requires the construction and analysis of pressure-volume (P-V) curves which are very time consuming. While P-V curves remain a valuable tool for assessing π_tlp and related traits, there is considerable interest in developing high-throughput methods for rapidly estimating π_tlp, especially in the context of crop screening. We tested the ability of a dewpoint hygrometer to quantify variation in π_tlp across and within 12 clones of grape vine (Vitis vinifera subsp. vinifera) and one wild relative (Vitis riparia), and compared these results to those derived from P-V curves. At the leaf-level, methodology explained only 4-5% of the variation in π_tlp while clone/species identity accounted for 39% of the variation, indicating that both methods are sensitive to detecting intraspecific π_tlp variation in grape vine. Also at the leaf level, π_tlp measured using a dewpoint hygrometer approximated π_tlp values (r² = 0.254) and conserved π_tlp rankings from P-V curves (Spearman's ρ = 0.459). While the leaf-level datasets differed statistically from one another (paired t-test p = 0.01), average difference in π_tlp for a given pair of leaves was small (0.1 ± 0.2 MPa (s.d.)). At the species/clone level, estimates of π_tlp measured by the two methods were also statistically correlated (r² = 0.304), did not deviate statistically from a 1:1 relationship, and conserved π_tlp rankings across clones (Spearman's ρ = 0.692). The dewpoint hygrometer (taking ∼ 10-15 min on average per measurement) captures fine-scale intraspecific variation in π_tlp, with results that approximate those from P-V curves (taking 2-3 h on average per measurement). The dewpoint hygrometer represents a viable method for rapidly estimating intraspecific variation in π_tlp, and potentially greatly increasing replication when estimating this drought tolerance trait in grape vine and other crops.