Source: https://grapesandwine.cals.cornell.edu/newsletters/appellation-cornell/2017-newsletters/issue-29-may-2017/research-plain-english/
Timestamp: 2019-04-19 18:42:53+00:00

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Wintertime cold temperature is the most important factor that influences grape distribution around the world. Most European varieties (Vitis vinifera) are not very cold hardy and suffer freeze damage in climates that reach -15 C or colder. Therefore, these varieties are not very well suited for grape growing regions outside of Mediterranean climates. In North America, particularly in colder winter climates like the Northeast, upper Midwest, and Canada, native grape varieties have genetic traits that allow them to survive much colder winter temperatures. As the grape and wine industry in these areas continues to expand, many grape growers are finding success in hybrids between V. vinifera and native North American grapes. In this study, the most comprehensive to date, researchers tested the cold hardiness of 33 different grapevines, including wild N. American species and hybrids, to characterize the cold hardiness ability of different genotypes. The results will help future grape breeding programs develop varieties from wild species better suited to cold climates.
To test cold hardiness of different grapevines, researchers used Differential Thermal Analysis (DTA). This method uses “thermoelectric modules” to measure a burst of heat released when water rapidly transforms into ice, also known as the low temperature exotherm (LTE). To measure LTE in grapes, dormant bud samples are placed in a freezer and run through a series of cooling cycles, where the freezer temperature steadily decreases over time. When the bud freezes, computer software records this spike in energy and the temperature at which it occurred (Figure 1). These LTEs can then compare to actual weather data measured within vineyard sites (NEWA) to see in real-time how grapevines will respond to temperature.
Figure 1. Example of LTE values for genotypes of V. riparia. X-axis shows time of winter (Nov 1 through budburst). The black line shows minimum daily temperatures (red line is 0 C).
Table 1. Sampled wild and hybrid grape varieties. GRIN ID is the USDA national plant network germplasm designation and GEO is geographic location.
Dormant grape buds were collected bi-weekly from the USDA germplasm from the first frost of the fall through spring budbreak.
Winter conditions. 2012-2013 mild winter, 2013-2014 cold punctuated winter, and 2014-2015 cold sustained winter.
LTE response of wild grapevines. Wild and hybrid varieties all showed LTE responses that mostly protected the vines from winter damage. In all species, LTE values were lower in 2013-2014 and 2014-2015 due to more exposure to colder temperatures throughout winter. Looking across winters, the Northern species (V. riparia and V. amurensis) had the lowest LTE, although the timing of greatest hardiness differed across years. In addition, LTE values changed as temperatures increased or decreased, and reached maximum hardiness at different times each year.
Cold hardiness and temperature response. Northerly wild grape species (V. riparia, V. labrusca, and V. amurensis) had the highest cold hardiness in all three winters, and showed more responsiveness to fluctuating midwinter temperatures. These species also had lower chilling requirements to fulfill dormancy and resumed growth faster (deacclimate) in the spring.
Northern vs. southern grape species. Southern species were not much less cold hardy than northern species. Southern species (V. amurensis, V. vulpina, and V. aestivalis) also showed less responsiveness to temperature fluctuations.
Breeding with northern N. American species may increase cold hardiness in hybrid grape cultivars. Northern species displayed the highest cold hardiness across all three years, however also deacclimated faster in response to warmer springtime temperatures. Compared to the North, winter conditions are milder in the South, but winter stability also decreases. As such, southern species may have evolved to resist temperature swings, whereas Northern species may have evolved to withstand harsher conditions and consistent cold. In the future, increasing winter temperature fluctuations may be the new norm in areas such as the Northeast. Increased cold hardiness from northern wild grape varieties may come at the cost of midwinter stability.
Finally, researchers noted that grapevines did not achieve their maximum cold hardiness in the vineyard throughout the study. This may mean that reaching maximum cold hardiness comes with a biological, energetic, or physiological cost.
Wild N. American grape species are more cold hardy than traditional V. vinifera varieties. By testing cold hardiness, this study suggests that hybrid varieties from these wild species may be more suitable for grape production in colder climates such as the Northeast, upper Midwest, or Canada. Yet, in selecting for these varieties, breeding programs should consider the local complexities found across a diverse range of climates.
To read more about testing grapevine cold hardiness (including data from across New York) please see: https://grapesandwine.cals.cornell.edu/extension/bud-hardiness-data.
Alex Koeberle ’13 is a program aid, Section of Horticulture, based at the NYS Agricultural Experiment Station in Geneva, NY.

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