MSU Extension Grapes

The nature of grapevines

The grapevine, belonging to the Vitaceae family, has a long history dating back to the Early Cretaceous Epoch, approximately 66-145 million years ago. Fossils of the Vitis genus have been discovered as far back as the Early Eocene period, around 34-56 million years ago, according to Pierre Galet in “General Viticulture.” This means that grapevines have existed for millions of years, coexisting with dinosaurs and predating the emergence of our hominid ancestors from Africa.

During this ancient era, grapevines survived and thrived through the natural processes of gene mixing and adaptation via natural selection. This was a time when the super-continent Pangaea gradually broke apart, leading to diverse climatic regions and placing various selection pressures on grapevine species. While humans were not present during this period, animals were attracted to grapes as a food source, aiding in the dispersal of seeds and further contributing to natural selection and adaptation processes.

Fast forward to the present, and our understanding of grapevine physiology has grown significantly, particularly in areas such as cold hardiness. Cold hardiness refers to a grapevine's ability to withstand freezing temperatures and encompasses several physiological processes throughout the year, according to Mohsen Niazian et al in “Betaine aldehyde dehydrogenase (BADH) vs. flavodoxin (Fld): Two important genes for enhancing plants stress tolerance and productivity.” This includes acclimating to cold temperatures in autumn, maintaining resistance during the coldest winter months, and gradually de-acclimating as spring approaches to avoid damage from late frosts.

Grapevine cold hardiness is influenced by various factors, including biochemical, cellular and anatomical characteristics controlled by the vine's genetic makeup. However, assessing cold hardiness can be challenging due to the complexity of these factors and the variability in weather conditions and stress events. In nature, grapevine species have evolved to thrive in specific environments, with genotypes best suited to their local conditions exhibiting greater cold hardiness and reproductive success. Within individual vines, variations in cold hardiness can be significant, necessitating precise sampling methods to evaluate tissue hardiness accurately.

Furthermore, grapevines have evolved adaptations to ensure survival and reproductive success. Dormant buds typically contain three potential shoots, with the primary shoot being the most advanced anatomically but also the least hardy. Loss of the primary shoot shifts production potential to secondary and tertiary shoots, allowing the vine to survive and continue its lifecycle. Overall, understanding grapevine cold hardiness and adaptation provides valuable insights for grape growers, helping them select appropriate varieties and implement effective vineyard management practices to mitigate the risks posed by freezing temperatures and other environmental factors.

Carbon assimilation and distribution in grapevines: Understanding sources and sinks in relation to cold hardiness

In the natural world, the key to the survival of perennial plants lies in their ability to capture carbon through photosynthesis and distribute essential molecules to various parts of the plant (Photo 1). This distribution process, known as carbon partitioning, is controlled by specific areas within the plant called sources and sinks. Sources, such as leaves and storage tissues, produce carbon compounds, while sinks are the sites where these compounds are utilized. The strength and location of these sinks vary, and their effectiveness may change throughout the growing season.

Maintaining and achieving cold hardiness in grapevines requires energy and specific metabolites, with various carbohydrates playing a role in protecting against freezing temperatures. Our research at Michigan State University has shown that stress on grapevines, such as aggressive leaf removal during and after veraison, can significantly affect cold hardiness in primary buds the following winter. This highlights the importance of ensuring optimal carbon accumulation and distribution to support vine resilience. Factors influencing carbon partitioning dynamics include proximity to the source (leaves), direct connection to the source, and the size and developmental stage of the sink.

Cold hardiness, along with other storage functions in roots and woody tissues, may not be prioritized for carbon accumulation compared to spring growth, fruit development and other immediate tissue needs. In summary, understanding the complex dynamics of carbon assimilation and distribution in grapevines is crucial for optimizing vine health and resilience to environmental stressors like cold temperatures.

Cultivating cold hardiness: The impact of vineyard management on vine resilience

As viticulturists, our goal is to nurture grapevines to achieve consistent yields and high fruit quality. In cooler climates, this nurturing process becomes even more crucial to fully express the vine's genetic potential for cold hardiness. However, cool/cold climate viticulture comes with its own set of limitations. Economic success in these regions depends on our ability to navigate and overcome these limitations through strategic choices. While some aspects of vine nurturing are within our control, such as vineyard management practices, others are influenced by external factors like climate variations. For example, in the Great Lakes region, variations in growing season length, temperature accumulation and precipitation can occur annually. While we can't control these factors, we can take steps to mitigate their impact.

One key consideration for viticulturists is understanding the balance between source and sink interactions within the vine. This involves determining when vegetative tissues and next season's buds become the primary sinks for nutrients. Since the fruiting cluster is the primary sink for most of the growing season, it's essential to ensure that vegetative tissues do not compete inadequately with the cluster for available nutrients. In summary, successful viticulture in cool/cold climates requires a strategic approach that optimizes vineyard management practices while mitigating the impact of external factors. By understanding the dynamics of source and sink interactions and making informed choices, viticulturists can maximize the expression of cold hardiness genes and achieve economic success.

Here's a concise overview of decisions and choices impacting vine expression of genes for cold hardiness, both in pre-plant and management phases. More information can be found on the Michigan State University Extension Grapes website.

Selection decisions: Pre-plant

Site selection: Understanding abiotic limits, particularly macro- and meso-climates, is crucial, especially in regions prone to freeze damage.

Cultivar selection: Consideration of site conditions is vital when choosing cultivars. Late-ripening varieties can challenge vine balance and therefore to cold hardiness, impacting fruit ripening and overall quality (Table 1). Early ripening varieties or hybrids can be prone to spring cold damages due to early nature in de-acclimation. Cultivar selection can affect the timing of budburst in spring, which is crucial for avoiding late frosts. According to research from Tommaso Frioni et all in “Impact of spring freeze on yield, vine performance and fruit quality of Vitis interspecific hybrid Marquette,” early-budding cultivars may be more susceptible to frost damage if they leaf out before the risk of frost has passed, while later-budding cultivars may have a natural advantage in regions prone to spring frost events.

Management issues: Establishment and production

Management goals should focus on sunlight penetration to leaves, adequate leaf area exposure, and efficient carbon distribution for storage and growth initiation. According to research from Stefano Poni et all in “Facing spring frost damage in grapevine: Recent developments and the role of delayed winter pruning–a review,” strategies such as specific pruning tailored to the cultivar of interest, canopy management and crop control are essential for maximizing vine expression of cold hardiness genes.

Maintaining balance in water and nutrient supply is crucial for vine health and hardiness. Both excess and deficiency can have detrimental effects. In recent years, several vineyards in Michigan have reported negative impacts of water stress and mineral nutrition due to climate change affecting grape-growing regions worldwide, including Michigan. Water stress can significantly disrupt vine mineral nutrition, thereby affecting cold hardiness. When vines undergo water stress, their capacity to absorb essential minerals like potassium and calcium from the soil may be compromised. These minerals are pivotal for the physiological processes linked to cold hardiness. Therefore, water stress indirectly influences vine cold hardiness by impeding mineral uptake and nutrient availability. To counteract the effects of water stress and optimize vine cold hardiness, it's essential to maintain proper irrigation practices and ensure adequate mineral nutrition. This proactive approach can help mitigate the negative impacts of water stress and bolster vine resilience in the face of changing climatic conditions.

In essence, the viticulturist's task is to manage vines in a manner that maximizes the expression of cold hardiness genes, ensuring resilience to freeze damage while maintaining overall vine health and productivity.