Description of fungi

Armillaria mellea * is an edible fungus that grows at the base of dead stumps in the fall.

• The carpophores are large, in very dense tufts and the cap is honey yellow (hence the name of the fungus: Honey armillary), without fibrils; on its underside it bears fruiting lamellae, white, then russet which produce ovoid and hyaline basidiospores (6-8 x 4-5 µm). The foot, also not fibrillated, is brown, very elongated, of constant diameter. The ring is well-formed, membranous, funnel-shaped, whitish or edged with yellow (Figures 1 and 2). In vivo , the mycelium is white, as previously described in the section on symptoms.
• Appearance on culture medium : A certain morphological diversity is observed in vitro (FIG. 4). Most strains of A. mellea produce rhizomorphs (Figure 5). The colonies have a crusty appearance, a mahogany brown color, and a shiny appearance. The mycelium is usually aerial at the edge of the colony or distributed irregularly. On the underside of the culture, we can see black rings corresponding to the formation of " black lines ".
  
  

* Note that at the end of the 1970s, the species, A. mellea which then grouped together all the fungi responsible for root rot in the various woody species, was split into several different species, including 5 for Europe. These species differ in particular in their host range and ecological requirements. The name of A. mellea was kept for the armillary subservient to deciduous trees, including the vine. Armillaria ostoyae , which attacks conifers, is never seen on vines. This explains the observations made by the ancients who observed that vine plantations on coniferous clearings were less attacked than those made on hardwood clearings.

Rosellinia necatrix can produce two types of fruit bodies during development.

• Its perfect shape is characterized by perithecia inserted on mycelial clusters, globular in shape, black, about 2 mm in diameter. These structures contain elongated, filiform asci (250-280 x 8-12 µm), containing 8 ascospores, arched measuring 5-8 x 30-50 µm.
• Its imperfect shape ( Dematophora necatrix Hartig) is at the origin of coremia erect 1.5 mm high, showing at their apical end conidiophores on which are produced conidia. The conidia are solitary, single-celled, elliptical to ovoid, smooth 3-4.5 x 2-2.5 µm. These coremia seem rare in nature and therefore play no role in the epidemiology of the disease.
• Appearance on culture medium : this fungus grows very quickly in vitro . Young colonies are white, fibrillated or downy in appearance; subsequently, they take on a dark gray color almost black and a crusty appearance. The downy mycelium is very characteristic because it presents swellings at the level of the mycelial partitions (Figures 6 and 7). It is possible to observe perithecia on older cultures.

Roesleria subterranea forms apothecia nail-headed , greenish-gray in color (Figure 8). Its mycelium is very easy to identify in vitro on a nutrient medium because it takes on a characteristic green-malachite tint.