Why do we have to graft vines?
In these days, some people might not be able to answer this question. The main reason is still a small insect, called phylloxera.
It was brought to Europe in the middle of the 19th century from North America. In 1874 it was the first time that it was found in Germany.
A fast growing diffusion of this pest resulted in a sharp decline of the area planted with vines. The phylloxera got real threat for the survival of the wine industry.
Because it only attacked the roots of the European vine-variety, they began to graft the European varieties like Riesling or Pinot noir on branches from American varieties which were tolerant to phylloxera. This was the beginning of vine grafting.
Grafting became very shortly an essential tool for the biological pest control against phylloxera, which it is still today.
Today, phylloxera is still a problem. California had to uproot thousands of hectars of vineyards, because the phylloxera found its way over the Rocky Mountains. Some of the rootstocks used there e.g. "AXR1" were not tolerant enough to it. This was a good chance for Phylloxera to spread quite fast and consequently lots of vineyards died.
For some years, we here in Germany and other countries can also recognize an increasingly occurance of phylloxera. For that reason everybody should only plant grafted vines, so everybody who still plants own rooted vines damages the commonalty.
Most of the rootstocks we use today are only tolerant and not resistant, this means if the population of Phylloxera is too high, they will also degenerate.
The above ground living individuals bit the leaves, and then a gall emerges at the underside of the leaves with a small hole one the upperside. In this gall the phylloxera lays more than 1000 eggs.
This is such a gall.
You can see an adult phylloxera (ca. 1 mm) and many newly-laid eggs around it.
Some of the lice hatching out of the eggs stay on the leaves and lay again eggs in a gall, others go into the ground an attack the roots.
Here you can see phylloxera in the soil, sucking on a root.
Ungrafted vines will decline from that. Phylloxera tolerant rootstocks bear this much better. Also the reproduction rate ist much more less then on own rooted vines.
Here you can see subteraneously laid eggs. Most of the lice hatching from this will stay in the ground.
But some of them will go to the surface and attach the leaves.
A big aim in breeding rootstocks is to get resistent varieties which cannot be attacked by phylloxera.
In the top left image you see a penetration by phylloxera and the emerged gall on a normal rootstock. The other three images show this on new breedings which are nearly Resistant against phylloxera.
One of these breedings is already in use, it is the variety Boerner.