Cabernet Blanc, Cabernet Jura, Muscaris, Souvignier Gris.
Do these varietal names sound familiar to you? From the sound of "Cabernet~", "Musca~", and "Souvi~", many of you may have guessed that these are wine grape varieties. Indeed, these are all names of wine grape varieties.
While you might not hear much about them today, there's a possibility that opportunities to encounter these varieties—and actually drink wines made from them—will increase in the future.
The Diversity of Grape Varieties and PIWI's Position
Grapes are believed to have existed on Earth at least 60 million years ago. Through their long history of natural crossbreeding and spontaneous mutations, it is estimated that 8,000 to 10,000 varieties now exist.
Of these, approximately 2,500 varieties are used for wine production. In recent years, while some indigenous varieties have fallen out of use, others have regained prominence due to climate change and a movement toward regional authenticity. Therefore, this number is constantly fluctuating.
Within this context, there exists a category that could potentially increase the total number of varieties in the future. This is the category classified as "PIWI," which is the focus of today's discussion.
What is PIWI?
PIWI is an abbreviation of the German term "pilzwiderstandsfähige Rebsorten." The term "Piwi" is gradually gaining international recognition. It refers to grape varieties that possess resistance to fungi that cause grape diseases.
As the name literally suggests, these are grape varieties that demonstrate high resistance to diseases caused by specific fungi. However, they are not naturally crossbred varieties—the vast majority are artificially crossbred varieties.
By creating grape varieties that did not previously exist in nature through artificial crossbreeding and using them for wine production, PIWI varieties serve as a factor that purely increases the total number of grape varieties used in wine production.
On the other hand, the process from acquiring characteristics through crossbreeding to actual market distribution—including various tests and field trials—requires a long period of time. Therefore, these varieties are not yet widely known.
While the expansion of planted acreage is currently gradual, since these variety groups have been developed to meet existing demand, as mentioned earlier, they are likely to gradually spread in the future.
Diseases That PIWI Varieties Resist
The disease resistance that consistently draws attention in this new category of wine grape varieties includes the following:
- Powdery Mildew (Echter Mehltau / Oidium)
- Downy Mildew (Falscher Mehltau / Peronospora)
- Gray Mold (Botrytis)
The reason these three diseases receive particular emphasis is that they pose the greatest threat to wine grape cultivation and are problematic worldwide—they represent the "three major diseases of the wine grape world."
Historical Background of Disease-Resistant Variety Development
The history of PIWI development dates back to the late 1800s. During this period, two of the three major diseases mentioned above—powdery mildew and downy mildew—were brought to Europe along with new varieties imported from America.
Many of you may recall the phylloxera crisis when hearing this story, and indeed, the background of these diseases is exactly the same, with the damage occurring during almost the same period.
These diseases, which had not previously existed in Europe, rapidly spread their damage. At the time, various countermeasures were attempted against this wildfire-like spread of damage. One of these was the crossbreeding of European varieties with American varieties, which became the foundation of PIWI.
Phylloxera primarily damaged grape roots, so damage was successfully controlled by using American varieties with resistance as rootstock. However, since fungal diseases directly infect the scion and spread damage, countermeasures using rootstock could not be implemented.
Therefore, two approaches were developed as effective countermeasure methods:
- Chemical control through spraying
- Acquiring resistance through crossbreeding
The currently effective countermeasure, as explained in the article "Cultivation Techniques | Disease Control in Grape Growing - Prevention Methods," is spray-based prevention conducted with appropriate content at appropriate times.
Methods of Acquiring Resistance
Just as the starting point of PIWI variety development was crossbreeding between European and American varieties, the acquisition of disease resistance—the greatest characteristic of this variety category—is achieved through inter-varietal crossbreeding. For this reason, grape varieties classified in this category are sometimes also called hybrid varieties or interspecific varieties.
To explain this point in more detail, varieties mainly called hybrid species have significantly different positioning from current PIWI varieties.
Most varieties called hybrid species were created through extremely simple crossbreeding between European and American varieties in the late 1800s to early 1900s. Taxonomically, these are not classified as Vitis vinifera.
In contrast, most PIWI varieties have been developed mainly since 1950. While crossbreeding with Asian varieties is also conducted for some varieties, through multiple rounds of crossbreeding with Vitis vinifera varieties, they taxonomically belong to Vitis vinifera.
In other words, PIWI varieties are realized by continuing to crossbreed hybrid varieties—which once ceased to be Vitis vinifera through crossbreeding with American or Asian varieties—further with Vitis vinifera varieties. They are varieties that retain the characteristic of disease resistance while approximating to a level taxonomically indistinguishable from Vitis vinifera.
Expected Roles of PIWI Varieties
The role expected of PIWI varieties is resistance to diseases that show signs of expanding damage due to climate change and other factors, but this has both economic and environmental significance.
The benefits of introducing PIWI can be broadly divided into the following two categories:
- Eliminating concerns about yield reduction due to disease
- Reducing spray frequency
The first can be positioned mainly as mitigation of economic damage, while the second has multiple meanings.
The Significance of Reducing Spray Frequency
Being able to reduce spray frequency leads to cost reduction for both the labor required for spraying and the chemicals used for application. When including peripheral costs such as tractor operation costs for application and water costs for mixing chemicals, this has a significant economic impact.
In addition to this, the perspective of reducing environmental burden through spray reduction and the associated sustainability has recently gained particular attention.
The chemicals applied through spraying are substances like copper and sulfur. While these are not necessarily chemically synthesized substances and are often naturally derived, heavy metals like copper are said to remain and accumulate in soil after application, becoming a factor in environmental burden. Reducing spray frequency directly leads to decreased chemical application amounts, thus directly reducing such environmental burden.
Furthermore, running tractors multiple times leads to compression of the soil surface layer, causing soil erosion such as topsoil runoff during rainfall, but reducing spray frequency also mitigates such problems.
The fact of not spraying also evokes an environmentally friendly image for customers, making it advantageous from a marketing perspective as well.
Summary | Will PIWI Really Spread in the Future?
We have seen that introducing PIWI—wine grape varieties with high disease resistance—can provide various benefits.
So, will the cultivation area of these varieties really increase in the future?
The answer remains unclear.
Certainly, global climate conditions continue to change, showing signs that conventional cultivation varieties may no longer be adequate. As a means to continue making wine, introducing PIWI varieties has both great significance and necessity.
However, winemakers are not satisfied simply with being able to make wine.
For producers, if there is no quality that they as winemakers can be satisfied with, there is no point in introduction regardless of what other benefits may exist. The stronger the pride that winemakers have in their work, the more pronounced this tendency becomes.
This point is one of the reasons why it is currently difficult to forecast whether the spread of PIWI varieties will expand in the future.
There is a lesson here.
Varieties once called hybrid varieties failed to show significant spread despite their utility being recognized, albeit partially.
Of course, one reason is the legal restriction in Europe that wine grapes must be Vitis vinifera species, but a more fundamental problem was the presence of off-flavors also called "foxy flavors."
Wines made from hybrid variety grapes were considered to have low quality due to the appearance of these foxy flavors, making them unsuitable for adoption as wine grapes.
Recalling our earlier explanation, while PIWI varieties are taxonomically classified as Vitis vinifera species, given their origins, they are not pure Vitis vinifera but rather varieties that closely approximate it.
Therefore, while not reaching the level of foxy flavors, many winemakers feel that variety-specific nuances remain that are undesirable for wine, sharing the same direction as those flavors. This represents the greatest current challenge for PIWI varieties and acts as a hindrance to their spread.
PIWI variety development continues continuously and is progressing by leaps and bounds.
Indeed, varieties have been developed where the varietal-specific aromas that were once quite pronounced can now hardly be detected.
Perhaps in the future, the number of these varieties will continue to increase further, and we may see a future where wines from this category constitute the majority of wines we commonly encounter.
