In the cool and humid climate of the northeastern United States, vegetation is typically maintained between the rows of wine grape (Vitis vinifera) vineyards, but the area directly beneath vines is conventionally kept bare using herbicides or cultivation, to reduce competition for water and nutrients. Yet with rising concerns of herbicide resistance, environmental contamination, and soil erosion, alternatives to maintaining bare ground in vineyards should be considered. In warmer and more arid climates, using cover crops as an alternative to bare soil has sometimes resulted in reduced vine growth and yields. In more cool and humid climates, like in the northeastern United States, where conditions can promote excessive vine growth, replacing bare soil with under-vine cover crops was hypothesized to improve vine growth characteristics and fruit quality from reducing excessive vigor. This study compared three annual under-vine cover crops of resident vegetation (RES), buckwheat (BW) (Fagopyrum esculentum), and annual ryegrass (ARG) (Lolium multiflorum), planted in the 1-m-wide strip directly under vines at the start of each growing season, against the conventional weed-free under-vine row maintained with glyphosate. The experiment was established in 2011 and repeated in 2012 and 2013 in a 20-year-old block of ‘Riesling’ wine grapes (clone 198 on S04 rootstock) in a commercial vineyard in the Finger Lakes region of New York State. Harvested grapes were fermented in duplicate using standard white wine procedures. Among the four under-vine treatments, no significant differences were found in measures of vegetative growth, yield, petiole nutrient concentrations at veraison, or predawn and midday stem water potentials. Under-vine treatments were not found to significantly affect soil organic matter, aggregate stability, and nutrient concentrations. Juice characteristics were also not significantly different among treatments. In this study, the mature vines in this rain-fed ‘Riesling’ vineyard likely had a well-developed and extensive rooting system that was able to overcome any competition effects for water or nutrients from the comparatively shallow root systems of the annually established cover crops. Without any induced competition in the conditions of this study, under-vine cover crops had no effects on vine growth, yield, or juice characteristics when compared with conventional herbicide use in the under-vine row. When multidimensional scaling (MDS) analysis was used to determine differences in aroma among wine treatment replicates, treatments were found to significantly impact the perceived aromatic properties of the wines, even though no measures of growth or juice characteristics were affected. Using under-vine vegetation may be a viable alternative to conventional herbicide use for vineyard floor management in mature wine grape vineyards in cool and humid climates.

Grafting joins two distinct plant parts: a scion (shoot system) from a donor plant and a rootstock (root system) from a second plant to which the scion is attached. The practice of grafting chiefly enables clonal propagation but can also have many other benefits, such as reducing the juvenility period (increasing precocity) or size (dwarfing) in fruit trees (Fazio et al., 2014; Warschefsky et al., 2016;Webster, 1995).In grapevines (Vitis vinifera L.), widespread use of grafting began in the late 1800s, following the introduction of phylloxera (Daktulosphaira vitifoliae Fitch) to Europe from North America. While

19Grape growers use rootstocks to provide protection against pests and pathogens and to modulate 20 viticulture performance such as shoot growth. Our study examined two grapevine varieties 21 ('Chardonnay' and 'Cabernet Sauvignon') grafted to 15 different rootstocks and determined the 22 effect of rootstocks on eight traits important to viticulture. We assessed the vines across five 23 years and identified both year and variety as contributing strongly to trait variation. However, the 24 effect of rootstock was relatively consistent across years and varieties, explaining between 9% 25 and 10% of the variation in growth-related traits including yield, pruning weight, berry weight, 26 and Ravaz index (yield to pruning weight ratio). Increases in yield due to rootstock were 27 generally the result of increases in berry weight, likely due to increased water uptake by vines 28 grafted to a particular rootstock. We determined that it is possible to achieve an over 50% 29 increase in yield, pruning weight, and Ravaz index by choosing the optimal rootstock, indicating 30 that rootstock choice is crucial for grape growers looking to improve vine performance. 31 32 157 158

Summary Annual rings from 30 year old vines in a California rootstock trial were measured to determine the effects of 15 different rootstocks on Chardonnay and Cabernet Sauvignon scions. Viticultural traits measuring vegetative growth, yield, berry quality, and nutrient uptake were collected at the beginning (1995 to 1999) and end (2017 to 2020) of the lifetime of a vineyard initially planted in 1991 and removed in 2021. X-ray Computed Tomography (CT) was used to measure ring widths in 103 vines. Ring width was modeled as a function of ring number using a negative exponential model. Early and late wood ring widths, cambium width, and scion trunk radius were correlated with 27 traits. Modeling of annual ring width shows that scions alter the width of the first rings but that rootstocks alter the decay of later rings, consistently shortening ring width throughout the lifetime of the vine. Ravaz index, juice pH, photosynthetic assimilation and transpiration rates, and instantaneous water use efficiency are correlated with scion trunk radius. Ultimately, our research indicates that rootstocks modulate secondary growth over years, altering physiology and agronomic traits. Rootstocks act in similar but distinct ways from climate to modulate ring width, which borrowing techniques from dendrochronology, can be used to monitor both genetic and environmental effects in woody perennial crop species.