Piwis = pilzwiderstandsfähige Sorten (= german which will mean: fungus resistant grapevine variety)
Since a few years, we call grape varieties, which are resistant (or nearly resistant) against fungus diseases often Piwis. These varieties only have to be treated against the most important fungus (Downey and Powdery Mildew) in a very limited extend.
This target was achieved by cross-breeding of resistant varieties with varieties of good wine quality. Most of these varieties are not completely resistant, however, the sprayings can be kept to a minimum, therefore these varieties are often only called fungus-hard.
The biggest problem of these varieties is the fact that their names are not known, and therefore you have to give a lot of explanations to sell these wines as varietal wines. The most important meaning these varieties have in organic viticulture, because it is much easier to make wine without chemical sprayings with these varieties.
These varieties used to be called hybrid vines (or even hybrids) because they are crossings of different Vitis species (usually with other Vitis vinifera). One of the first breeders, which dealt with the breeding of such hybrids was Albert Seibel, a French doctor and vine breeder. He began in the late 19 Century when phylloxera had just arrived in France, and within a few years had destroyed a very large space of the French vineyards. Seibel hoped that he could get phylloxera resistant varieties by crossbreeding phylloxera-resistant species from North America. This was successful, but unfortunately, the wine quality of these varieties was not comparable with European varieties, so France has banned all hybrid by 1960. From that date, the interspecific varieties were frowned upon in many years.
Some breeders above all Germans, however continued these crossings, even with cross results of Seibel. But the aim was now to get fungus resistant varieties. The quality of the wine could be increased, so that nowadays the progenys of these varieties are marked as Vitis vinifera in the list of varieties with very good wine quality.
Today, especially in the following research Institutes offer fungus resistant varieties:
Research Institute Geisenheim
Julius Kühn Institute
The first member of this group, which reached a certain spread was the Regent. In the last few years some more varieties found their way to the market.
In particular, the Weinbauinstitut from Freiburg has brought, several new PIWIS on the market. Some of them such as Johanniter, Bronner, Solaris, Cabernet Carbon and Cabernet Cortis are already registered as Vitis vinifera from the Bundessortenamt to the list of varieties in Germany.