Notes from Grapes (2nd Edition) by Creasy & Creasy

1. History, Uses and Production

Vitis includes many species, including V. vinifera, the most widely planted grape species in the world, which is used primarily for wine, table consumption, juice and raisin production.

Natural Growth Conditions

V. vinifera is much more tender, and generally cannot withstand temperatures below -15°C without suffering damage.

Unlike tree fruits, e.g. apple or pear, which set a terminal bud as winter approaches, grapevines will continue to grow as long as conditions are met.

Uses

The grape attains a high concentration of sugar when ripe, and also (depending on cultivar) pectin, as well as a wide range of aromatic compounds. These factors, in concentration with the presence of relatively high levels of acids (particularly tartaric acid), mean that the fruit is amendable to many different end uses.

Fermented Grape Products

Evidence that humans were fermenting grapes with the specific purpose of making an alcoholic beverage can be traced back to around 7000 BC in China, in the Near East around 6000 BC. There is an association between grapes and various types of yeasts (usually living on the surface of the berry), so it is likely, at least initially, that fruit which had been picked and stored may have started fermenting naturally.

Wine can be thought of as a naturally made storage form of the fruit as it retains characteristics of the grape and, protected from oxidation, can remain palatable for many years.

2. Cultivars, Anatomy and Improvement

Main Cultivars for Various Uses

The Organisation Internationale de la Vigne (OIV) list approximately 250 cultivars as being significant to the wine industry, and many more recent data state that 33 cultivars are responsible for 50% of the global vine area, and 13 cover more than 33%.

Clones

In practical terms, a clone is a selection of a cultivar that has some distinguishing characteristic that someone noticed and thought was significant enough to warrant separate propagation of the vine.

Examples of characteristics that may be used to select a clone are vine growth (vigour), disease resistance, leaf or shoot appearance, cluster shape, fruitfulness, fruit composition, etc.

In a practical sense, clones have value because they are all the same variety, but not quite.

In general, it is good practice to have a few different clones in a planting to spread some of the risk by having slightly greater genetic diversity, while still being able to produce a varietal product.

Anatomy and Physiology

The grapevine structure is very similar to that of many other woody perennials. It has a root system that serves to anchor the plant in the ground but also gathers and sends water and nutrients to support plant growth and acts as a carbohydrate reservoir for carrying over energy from season to season. There is also a trunk, which serves as structural, carbohydrate storage and conduit roles, and the branches (called canes or cordons) that support the shots, fruits, and leaves.

Roots

The root system is made up of the larger arms and branches, down to root tips and root hairs. The latter organ is the workhorse of the root system, where the vast majority of nutrient and water update occurs.

The root system, as does the shoot system, produces plant growth regulators that can modify the growth of the other parts of the vine.

Mycorrhizae

These are a group of fungi that form beneficial relationships with most species of plant, including grapevines. In trees, shrubs and woody perennial vines, vesicular-arbuscular mycorrhizae (VAM) are the most common. These are symbiotic relationships, as both the plant and the fungi benefit.

I highly recommend reading Entangled Life: How Fungi Make Our Worlds, Change Our Minds & Shape Our Futures by Merlin Sheldrake.

The exploration of soil is very important to the survival of the vine. Some nutrients, such as phosphorous, are immobile in the soil and thus, for the plant to obtain a supply of it, the roots must grow into areas of soil that have those nutrients available. This is unlike a nutrient like nitrogen, which is mobile in the soil solution and is brought to the roots by water percolating through the soil profile.

Roots grow in all directions and, if an area of higher nutrient or water availability is grown into, there is a more rapid proliferation of roots there.

Management decisions, such as the severity of pruning, also affect root life, with more severe pruning reducing the average lifespan of a root. Those parts of the root that continue to develop become more permanent branches and are a site for carbohydrate storage,

Above the Soil

The above-ground parts consist of the trunk, which is the portion of the vine from the ground to about the fruiting wire and provides support for canopy growth as well as being a carbohydrate storage site. Also shown are new canes, which were the previous year's shoots and a non-count cane, which are shoots arising from buds buried in the bark (formerly at the base of shoots).

It took me a while to understand why we distinguish shoots/branches by age. I only understood why after learning why and how to prune vines. In short, flowers (therefore, fruits) only grow out from a fresh shoot, and shoots grow from the buds located at nodes. Therefore, we need to choose a shoot to become the cane (almost 1 yr old shoot at the time of/after harvest) from which fresh shoots will grow with flowers.

Along the cane are nodes, separated by internodes. At this point in the season, the nodes are where the following season's shoots will arise. Positioned at alternate sides of the cane are compound buds, so called because they contain three (the primary, secondary and tertiary) pre-formed shoots. Each of these will have six to nine leaf primordial and, in some cases, flower cluster primordial already formed.

It is worth noting that grapevines do not form adventitious or spontaneously formed buds – all shoot growth originates from a previous node position.

Therefore, we must be thinking for at least two years (the current season and the next) at all times when we are taking care of the vines.

Photosynthesis

The workhorse of photosynthesis is the chloroplast, which collects light energy using primarily chlorophyll. Chlorophyll appears green because it absorbs most red and blue wavelengths of light. The light energy collected is used to split water molecules (H2O), adding the hydrogen (H) to carbon dioxide (CO2) to form carbohydrates (CHO) in the form of sugar (glucose). As a result of this process, oxygen (O2) is released.

Ingredients that the photosynthetic process needs are light, moderate temperature, CO2 and water. Temperature also influences respiration, where its rate increases the warmer it gets.

Specialized guard cells form the pore when the cells become turgid, and the pore closes when the cells lose water. In this way, there is an efficient method for the vine leaf to regulate the passage of gases, including water vapour, in and out of the leaf. When the vine has a good water supply, the guard cells are turgid and the stomatal pores are open; when the vine suffers water stress, the guard cells become flaccid and the pores close.

From Google.