Main symptoms

Telluric symptoms

• Amillaria mellea affects roots whose bark turns brown and peels off easily, in the absence of visible external mycelium. On the other hand, one can observe, between the bark and the wood, a network of ribboned cords and white palmettes (figures 1 and 2). This network can come together to form an almost continuous mycelial sleeve which can go up to the neck of the plant.
  At a more advanced stage, black lines appear under the bark; they are in fact a kind of melanized mycelial lamina delimiting, inside the root, protective volumes for the fungus (figure 3).
  At the final stage of colonization, the wood is completely degraded, fibrous in appearance, spongy, orange-yellow in color, saturated with water. We are then in the presence of a "wet rot". A strong mushroom odor emerges (Figure 4).
  Sometimes, we note on the roots the presence of rhizomorphs, kinds of dark brown to black cylinders, smooth and shiny, 1 to 1.5 mm in diameter and ten or more centimeters long. of the armillaria, tufts of carpophores honey-yellow are visible at the feet of vines that die in autumn (figures 5 and 6).
• Rosellinia necatrix causes different symptoms from the previous ones. Outside the root, when the climatic conditions are favorable (high relative humidity), we observe white mycelial webs becoming smoky gray, very abundant but very fragile, having the appearance of a spider's web (facies to the origin of the name of this disease). More generally, we note the presence of white cords of loose structure that can also be found in the interstices of the ground.
  Under the bark, the palmettes are small, slender, fan-branched. They never constitute a continuous mycelial sleeve between the bark and the wood as in the case of Armillaria, they are distributed throughout the bark which presents, according to Guillaumin (1982), a "marbled" appearance. The wood is apparently not degraded.
• Roesleria subterranea produces a mycelium which does not appear on the surface of invaded roots. This one, very thin (1 µm in diameter), is intra and intercellular. It disrupts woody tissue that is often already weakened for other reasons. Its numerous fruiting bodies are easily observed along the roots; they are apothecia in the shape of a nail head, of a greenish gray color, forming mainly in the fall.
  
  

Aerial symptoms

• a slow form characterized by a progressive dieback of the plant which dwarfs and presents buds which abort. The internodes are shorter, the leaves smaller but generally not deformed. Sometimes, in mid-summer and depending on climatic conditions, the leaves of white grape varieties turn yellow and those of black grape varieties redden, this before premature defoliation (figures 7 to 10);
• an apoplectic form at the origin of a sudden generalized or partial wilting of the vine. In the latter case, one or more dead arms may be observed the following year. The leaves eventually wither and drop. It should be noted that this apoplectic form can occur on apparently healthy vines which are generally very fruitful or on vines that are already dying.
  
  

The diseased vines are distributed randomly at the start of the attack, but very quickly we observe foci ("circles") showing dead plants in their center and dying off at the periphery. This distribution in focus is at the origin of the name "diseases of the round" also associated with these rots (figure 9).