Terroir and rootstock effects on leaf shape in California Central Valley vineyards

• Embedded in a single leaf shape are the latent signatures of genetic, developmental, and environmental effects. In viticulture, choice of location and rootstock are important decisions that affect the performance and production of the shoot. We hypothesize that these effects influence plant morphology, as reflected in leaf shape.

• We sample 1879 leaves arising from scion and rootstock combinations from commercial vineyards in the Central Valley of California. Our design tests 20 pairwise contrasts between Cabernet Sauvignon and Chardonnay scions from San Joaquin, Merced, and Madera counties from vines grafted to Teleki 5C, 1103 Paulsen, and Freedom rootstocks.

• Using geometric morphometric approaches, we visualize a morphospace in which, in addition to clear separation of Cabernet Sauvignon and Chardonnay scion leaf shapes, an orthogonal source of shape variation affects both varieties. Comparing the Procrustes distances to within and between group means, the additional source of variance is found to arise from location and rootstock effects.

• We describe and visualize a specific shape feature, the angle of the proximal lobe to the midvein that defines the closure of the petiolar sinus, that is attributable to location and rootstock effects and orthogonal to and separate from genetic, developmental, or allometric effects attributable to leaf size.

Societal Impact Statement (EN)

The innumerable effects of terroir—including climate, soil, microbial environment, biotic interactions, and cultivation practice—collectively alter plant performance and production. A more direct agricultural intervention is grafting, in which genetically distinct shoot and root genotypes are surgically combined to create a chimera that alter shoot performance at a distance. Selection of location and rootstock are intentional decisions in viticulture to positively alter production outcomes. Here, we show that terroir and rootstock alter the shapes of grapevine leaves in commercial vineyards throughout the California Central Valley, documenting the profound effects of these agricultural interventions that alter plant morphology.