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) is gaining attention as an indicator of drought tolerance in plants, though estimating π 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 and related traits, there is considerable interest in developing high-throughput methods for rapidly estimating π, especially in the context of crop screening. We tested the ability of a dewpoint hygrometer to quantify variation in π 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 while clone/species identity accounted for 39% of the variation, indicating that both methods are sensitive to detecting intraspecific π variation in grape vine. Also at the leaf level, π measured using a dewpoint hygrometer approximated π values (r = 0.254) and conserved π 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 for a given pair of leaves was small (0.1 ± 0.2 MPa (s.d.)). At the species/clone level, estimates of π measured by the two methods were also statistically correlated (r = 0.304), did not deviate statistically from a 1:1 relationship, and conserved π 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, 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, and potentially greatly increasing replication when estimating this drought tolerance trait in grape vine and other crops.