ARMILLARIA MELLEA: CHARACTERISTICS, HABITAT AND DISEASES - BIOLOGY - 2025

Armillaria mellea is a species of macroscopic multicellular fungus that frequently acts as a plant pathogen. It is the causative agent of the so-called “white sore” or root rot, which is why it is considered an extremely harmful and dangerous pest.

Attack by Armillaria mellea on the many susceptible plants causes rotting of the roots, preventing the absorption of water and nutrients from the soil, and subsequent death. The disease is common in moist, compact soils, where the roots are in conditions that promote suffocation.

Figure 1. Compact masses of Armillaria mellea individuals infecting a tree trunk. Source: Skookshroomer76, from Wikimedia Commons

Many plant species are susceptible to infection by Armillaria mellea, such as: cocoa trees, avocados, mangoes, peaches, apple trees, cherry trees, pistachios, plums, almond trees, papaya, vines, apricots, persimmons, kermes oak, rose bushes, among others.

In some localities, this fungus is used as an edible species and is part of the pharmacopoeia of traditional Chinese medicine, but great caution is recommended in its consumption, since it can cause intoxications whose symptoms are known.

characteristics

Morphology

Pileus or hat

It is the part of the fungus that contains the blades, which house the spores. The Armillaria mellea hat, having reached its maximum development, can be up to 15 cm in diameter.

The shape can be spherical, convex, flattened, or wavy, with increasing age. It is honey colored; hence the designation for its species "mellea" (honey or yellow in Latin).

The cuticle of the hat is easily detachable and frequently has small, brown, fleeting scales that can disappear with the rain.

Hymenio

The hymenium is the fertile part of the fungus . The Armillaria mellea species has numerous plates, morphologically of the subdecurrent type, due to the way in which they join with the foot, as they extend in a thread going down this structure.

These plates are slightly tight and present creamy white color and yellow spots when the fungus is young; later they turn yellow and in old age they show a reddish or brown color.

Figure 2. Armillaria mellea. The brown spots, the convex and flattened-wavy shapes of the hat and the long, curved foot are observed. Source: Pixabay.com

Stipe, foot or peduncle

The foot is the structure that supports the crown or hat. The foot of Armillaria mellea is very long, cylindrical, fusiform, curved, elastic, fibrous, of a pale cream-brown color that turns brown-ocher with time.

It has a broad, persistent, membranous, whitish ring. The lutea variety has a yellowish ring. The Armillaria mellea groups form a firm and compact mass at the base of their feet.

Constitutive tissue or "flesh"

The meat is woody and fibrous in the area of ​​the foot and whitish, firm, in the cap. It has a strong, unpleasant odor. The taste turns bitter in adult specimens.

Mycelium

The mycelium of a fungus is made up of a set of hyphae or cylindrical filaments whose function is nutrition.

The Armillaria mellea fungus develops a network of rhizomorphs or mycelium cords, formed by linear aggregates of parallel hyphae, with the appearance of roots. Rhizomorphs infect the entire tree and have the ability to spread to other neighboring plants.

Nutrition and lifestyle

Fungi do not have chlorophyll, or any other molecule capable of capturing solar light energy, therefore they are not capable of producing their food by photosynthesis, and must feed on substances that they take from other living or dead organisms. Their way of life can be as parasites, saprophytes or symbionts.

It is recommended to trust only the determinations made by specialist mycologists and health centers in each country.

Eating diseases

The Armillaria mellea mushroom is considered an edible species in many localities, however, great caution is recommended when using it as food, as it can cause poisoning.

Consumption of Armillaria mellea produces the so-called late muscarinic syndrome, with a latency period greater than 6 hours. The sudorian muscarinic picture that it produces is manifested in the following symptoms:

-Sialorrhea or hypersalivation.

-Sweating.

-Tearing.

-Bronchorrhea or excessive secretion of mucus from the bronchial tubes.

-Bronchoconstriction, cough, shortness of breath.

-Miosis or contraction of the pupil and lens of the eye.

-Blurry vision.

-Intestinal colic.

-May cause hypotension and bradycardia or a decrease in heart rate.

The treatment of this intoxication is symptomatic and supportive with hydration. If hypotension and bradycardia occur, atropine administration is required; a drug antagonist of the aforementioned muscarinic effects.

References

1. Baumgartner, K., Fujiyoshi, P., Ledbetter, C., Duncan, R. and Kluepfel, DA (2018). Screening Almond Rootstocks for Sources of Resistance to Armillaria Root Disease. Horts Science. 53 (1): 4–8. doi: 10.21273 / HORTSCI12038-17
2. Mesanza, N., Iturritx, E. and Pattena, C. (2016). Native rhizobacteria as biocontrol agents of Heterobasidion annosum s. and Armillaria mellea infection of Pinus radiate. Biological Control. 101: 8-16. doi: 10.1016 / j.biocontrol.2016.06.003
3. Obuchi, T., Kondoh, H., Watanabe, N., Tamai, M., Imura, S., Jun-Shan, Y. and Xiao-Tian, ​​L. (1990). Armillaric Acid, A New Antibiotic Produced by Armillaria mellea. Medica plant. 56 (2): 198-201. doi: 10.1055 / s-2006-960925 Chemical
4. Vaz, JA, Barros, L., Martins, A., Santos-Buelga, C., Vasconcelos, H. and Ferreira, I. (2010). Chemical composition of wild edible mushrooms and antioxidant properties of their water soluble polysaccharidic and ethanolic fractions. Food Chemistry. 126 (2): 610-616. doi: 10.1016 / j.foodchem.2010.11.063
5. Yang, J., Yuwu, C., Xiaozhang, F., Dequan, Y. and Xiaotian, L. (1984). Chemical Constituents of Armillaria mellea Mycelium I. Isolation and Characterization of Armillarin and Armillaridin. Medica plant. 50 (4): 288-290. doi: 10.1055 / s-2007-969711