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Grapevine leaves have diverse shapes and sizes. Their shape and size is known to be influenced by genetics, vine phytosanitary status, environment, leaf and vine age, node position on the shoot, shoot order, and other factors. In order to determine the importance of grapevine leaf shape and size to canopy temperature, we examined the relationship in five seedling populations grown in a vineyard in the San Joaquin Valley, California, USA. The seedlings were individual genotypes and unreplicated. All of the populations had one parent or grandparent with compound leaves of the Vitis piasezkii type and each population had a different second parent with non-compound leaves. As expected based on published reports and our own observations in related populations, the V. piasezkii compound leaf phenotype segregated as a dominant or semi-dominant trait and the populations all showed noticeable segregation for leaf shape. We measured leaf shape using 21 homologous landmarks. We used an infrared thermometer to measure the temperature of the canopy in July and August 2018 and 2019. By recording time of sampling and temperatures, we were able to determine which vines were cooler or hotter than expected, using a linear model. We did not measure canopy architecture, photosynthesis, or water use efficiency, as the heterogeneity of individual seedling canopies is very high, and this substantially complicates these observations on unreplicated seedlings. We established a relationship between leaf size and leaf temperature: vines with larger leaves were cooler than expected. In contrast, leaf shape was not strongly correlated with variation in vine temperature. Ultimately, these findings indicate that vines with larger leaves may contribute to the reduction of overall vine canopy temperature, but further work is needed to determine if this is due to variation in leaf size, differences in the openness of the canopy, or other related traits. [ABSTRACT FROM AUTHOR]

Societal Impact Statement Summary 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 alters 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. 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. We quantify clear differences between Cabernet Sauvignon and Chardonnay leaves. However, we also detect a separate, statistically independent source of shape variance that affects both Cabernet Sauvignon and Chardonnay leaves similarly. We find that this other shape difference is associated with differences in rootstock and location. The shape difference that arises from rootstock and location affects the basal part of the leaf near the petiole, known as the petiolar sinus, and affects its closure. This shape effect is independent from previously described shape differences that arise from genetic, developmental, or size effects. [ABSTRACT FROM AUTHOR]