The hidden outcomes of clonal selection: cultivar-specific water-use efficiency dynamics in grapevine (Vitis vinifera L.)

Abstract

Clonal selection represents a key approach in the genetic improvement of grapevines. Its primary objective is to fix, within commercial clones, the cumulative somatic variations that have arisen over time in vegetatively propagated vineyards and that confer valuable agronomic traits. Traditionally, breeding programs have emphasized traits such as yield, berry composition, and sanitary status; however, it is plausible that certain, yet largely unexplored, adaptive responses to abiotic stress have also been unintentionally preserved in distinct genetic backgrounds. In the present study, ten Vitis vinifera varieties—represented by their most commercially relevant Italian clones—were evaluated under uniform field conditions in an experimental vineyard. Measurements of isotopic composition (δ¹³C and δ¹⁵N) and proximal physiological traits (stomatal conductance, gs, and SPAD readings) were collected across three consecutive seasons (2022–2024) to investigate intra-varietal diversity in intrinsic water-use efficiency (iWUE). Results revealed significant variation (p < 0.001) across all traits examined, with the Year factor frequently significant, reflecting strong interannual fluctuations in temperature and precipitation. REML analyses indicated that both Variety and Clone contributed substantially to total variance, and broad-sense heritability (H²) was high for δ¹³C (0.75), δ¹⁵N (0.58), and SPAD values (0.48). Conversely, in vivo gs measurements showed lower heritability estimates. Intra-varietal BLUPs for the heritable parameters highlighted marked within-cultivar variability—particularly in Sangiovese, Pinot noir, and Cabernet Sauvignon—for δ¹³C, suggesting the coexistence of clones exhibiting distinct strategies for stomatal regulation and transpiration efficiency. Correlation analyses also revealed temporal patterns of selection, with more recently developed clones tending to display lower iWUE combined with higher average bunch weights. Overall, this work demonstrates substantial intra-varietal genetic variability for traits linked to stress tolerance while identifies discernible trends in clonal selection associated with reduced water-saving behaviour in later selections.