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Leaf curl virus (Grapevine FanLeaf Virus - GFLV)
Known already in the late 1800s in France, the virus is widespread wherever vines are grown. The extent of the damage reported is extremely variable, influenced by cultivars, rootstocks, age of the vines and form of farming / management. In some cases, production damage has been reported up to 50%
The symptomatological picture can be very variable. Two groups of symptoms can be distinguished:
infectious deformations: jagged, malformed leaves, very open petiole sinus, shoots with short internodes, double knots, bandages;
yellow mosaic: presence on the leaf layer of yellow patches, more or less extended which may also affect the entire leaf plate; evident symptoms in spring (disappears in summer).
In all cases, there is little fruit set, reduction in the number and size of the bunches and flower abortion (Marenghi, 2007).
Nematode Xiphinema index allows the spread of the virus in nature: the infected nematodes are rather mobile and persistent in the soil and make it difficult to restore infected areas.
The spread in the virus in exempt areas is mainly due to the use of infected propagation material.
The optimal periods for the loss of symptoms are:
May / June: color alterations, bandages;
winter, before pruning: alterations of the shoots.
It is important not to confuse leaf curling linglialia with nitrogen or iron deficiency and yellowing due to herbicides. The ELISA test, a precise serological technique, is useful, which completely casters the virus: it is the easiest and fastest method to test a large number of samples, with the possibility of multivirus analysis on a single winter extract.
The control of this disease is based on prevention, through:
use of virus-free propagation material;
vector control: if vector nematodes are present, a rotation of a couple of years is carried out with non-susceptible or biofumigant crops;
introduction of resistance genes.
Vine leaf curling
Leaf foliation (leafroll, LR) is one of the most important vines of the vine, both for its remarkable diffusion (it is present in all the wine growing areas of the world) and for its economic impact. The first reports of this disease date back to the second half of the 19th century.
LR is a complex etiology disease associated with eight different filamentous viral entities belonging to the family Closteroviridae. These viruses have been called Grapevine Leaf Roll associated Virus (GLRaV). Nine different types have been identified, which have been assigned a progressive numbering as they were discovered: GLRaV-1, -2, ..., -9.
The symptoms of LR are evident on most European grape cultivars (Vitis vinifera), instead they remain latent on almost all American rootstocks. The European vine cultivars most sensitive to leaf curling are:
black berry: Pinot noir, Cabernet franc, Cabernet sauvignon, Barbera;
white berry: Riesling, Cortese, Chardonnay.
They initially affect the basal part of the branches, then progress towards the apical areas. The leaves undergo a downward curvature of the leaf margins (starting from the basal leaves) and subsequently color alterations (excluding ribs): yellowing in the white berry cultivars and redness in the black berry ones. The bunches ripen late and unevenly, they are also less numerous and have smaller berries with reduced sugar content. The result is a reduction in production in both quantitative and qualitative terms (the drop in production can even exceed 50%).
The disease causes the degeneration of phloematic tissues and the accumulation of starch in the leaves, while the sugar content of the berries is lower than normal.
The first external symptoms of leaf curling are visible in early summer; as the season progresses, they intensify until they reach their maximum expression in the autumn.
The leaf curl virus is transmitted through the use of infected propagation material in vine plants.
In nature, however, it is transmitted by vectors such as coccidia (Pulvinaria vitis Linnaeus) and pseudococcids (Planococcus ficus Signoret, Planococcus citri Risso, Pseudococcus longispinus Targioni Tozzetti, Pseudococcus viburni Signoret, Pseudococcus calceolarie Maskell, Pseudococcus calimus.
The defense against the leaf curling of the vine is carried out mainly through preventive practices:
production and use of certified healthy propagation material;
maintenance of nurseries through insecticide treatments targeted against disease vectors.
Leaf curling on Barbera (source: www.riccagioia.it)
Curly vine wood
Under this denomination we mean a syndrome that can be caused by 4 different diseases:
Pitting of Vitis rupestris
Groove of LN33
Syou should tell
Symptomatology usually borne by the rootstock, which is altered at the exchange and xylem level by buterrature and grooves, with reduced functionality and often confused with graft disaffinity. Possible death of the rootstock and therefore of the entire plant. In general, dwarfism, stunted growth, leaf yellowing, considerable diametric difference between the two blondes is observed.
Diffusion occurs through grafting with infected material and through Coccides and Pseudococcides.
Symptoms are not always typical in the aerial part; important is to look at the rootstock, peeling it. Symptoms are typical on indicator screws like Vitis rupestris, but the response times are long (2-3 years). Also useful in this case is the diagnosis by ELISA.
Also in this case the control is based on prevention: production of healthy propagation material and control of the vectors.
Curly wood (source: www.patvite-pstsicilia.it)
Fact sheet by Enrico Ruzzene