Grapevine & Wine 01/10/2012

New defenses against phylloxera and Grapevine fanleaf virus

Some recent discoveries could be extremely effective in ameliorating the genetic characteristics of vines to fight these two dangerous vine diseases

The Grapevine fanleaf virus (or simply Gflv) is a dangerous pathogen transmitted by nematodes, and presents a clear symptomatology: fan-shaped leaves, abnormal dimensions and color of the leaves (yellowish dots on the leaf surface and nervatures), a general deterioration of the plant, a high number of flower aborts and smaller and lower quality grapes. In these conditions the vine has a very low life expectation.

Since there is no effective defense against nematodes, the only possibility in case of Gflv attack is to wait at least seven years before reusing the land.

On the other side phylloxera is an aphid that provokes big galls, or nodosities, on the roots with a resulting impairment in the absorbing capacity of them. At the same time, round and coarse galls appear also on the inferior surface of the leaves, producing a weird and irregular shape of the leaf. The diminished absorbance capacity of the roots leads to a progressive death of the plant.

Up to date, the only defense against phylloxera is the employment of rootstocks resistant to the generation of the insect that attacks the roots; as a matter of fact, this is the only generation of the insect that provokes economic damages. Excellent results where also provided by crossing the European with the American vine, but in the last years some species of phylloxera able to attack the American varieties appeared, too.

Hence, the only possibility against both these diseases is the continuous genetic improvement.

As for phylloxera, in particular, some good results seem to be granted by the employment of the rootstock called Börner. This is a crossbreeding between Vitis riparia 183G and Vitis cinerea Arnold. This approach was tested by crossbreeding the varieties Börner and Gf.V.3125 and then injecting phylloxera. The resistance to the parasite has been linked to a specific gene present on the chromosome 13 of the Börner variety. This can be very useful to future programs of reproduction.

On the other side, the hope against Gflv comes from Italy, from the Moscato grapes (Rotundifolia Muscadinia). Besides the intrinsic difficulty in producing crossings for rootstock in this case, is has been possible to produce an hybrid, called Rpg1, which shows a high level of resistance to Gflv. As a matter of fact, this crossing is not really preventing the entry or the propagation of the virus, but it is just slowing it very much. Over four-year observations indeed, the virus showed the ability to infect the plant anyway.

di R. T.