A high-throughput approach for quantifying turgor loss point in wine grapes

Abstract

Abstract Quantifying drought tolerance in crops is critical for agricultural management under environmental change, and drought response traits in wine grapes have long been the focus of viticultural research. Turgor loss point (πtlp) is gaining attention as an indicator of drought tolerance in plants, though estimating πtlp often requires the construction and analysis of pressure-volume (P-V) curves which is time consuming. While P-V curves remain a valuable tool for assessing πtlp and related traits, there is considerable interest in developing high-throughput methods for rapidly estimating πtlp, especially in the context of crop screening. We tested the ability of a dewpoint hygrometer to quantify variation in πtlp across and within 12 varieties of wine grapes (Vitis 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 πtlp while variety/species identity accounted for 39% of the variation, indicating that both methods are sensitive to detecting intraspecific πtlp variation in wine grapes. Also at the leaf level, πtlp measured using a dewpoint hygrometer significantly approximated πtlp values (r2 = 0.254) and conserved πtlp 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 πtlp for a given pair of leaves was small (0.1 ± 0.2 MPa (s.d.)). At the species/variety level, estimates of πtlp measured by the two methods were also statistically correlated (r2 = 0.304), did not deviate statistically from a 1:1 relationship, and conserved πtlp rankings across varieties (Spearman’s ρ = 0.692). The dewpoint hygrometer (taking ~ 10–15 minutes on average per measurement) captures fine-scale intraspecific variation in πtlp, with results that approximate those from P-V curves (taking 2–3 hours on average per measurement). The dewpoint hygrometer represents a viable method for rapidly estimating intraspecific variation in πtlp, and potentially greatly increasing replication when estimating this drought tolerance trait in wine grapes and other crops.