Effects of Armillaria species on forests

Armillaria species are a nuisance to forests as they cause secondary infections through root rot and are responsible for clearing out of woods. Their distribution depends on how a forest managed and species preference to climate and type of trees affected. This section seeks to discuss all these factors observed in the study findings. Different species with their morphological and phylogenic characteristics based on the methodology findings will also be addressed in this section.

Management and Armillaria species existence

Forest management has a tremendous effect on the distribution and survival of Armillaria species. Forest with poor management was found to be less susceptible to Armillaria species attack. Presence of SO2 and other pollutants are known to affect Armillaria existence. Its infections are not common in polluted forests; however, in well-managed forests, most trees were found to be affected by Armillaria root infection. Soils with heavy metal such as lead were found to have minimal growth of mycelia and Rhizomorph if none. Land management is known to impact the host-parasite association. Lands with depleted iron due to pastoral practices are known to be prone to Armillaria. Other practices too such as thinning aid in the spread of Armillaria species, lands which have had thinning practiced in it presented high levels of root rot infections spread, especially in young trees. It was confirmed as Nörreskog was more prevalent as thinning had occurred in the area before.  Also in lands which were previously cleared and left exposed to heat from the sun exhibited reduced infections, Nörreskog area confirmed this hypothesis a more sample collected from these areas and the. It occurs since the roots are protected by sunlight. Areas with oomycetes, had an elevated prevalence of infections as oomycetes, catalyze predisposition especially in deciduous trees. Areas with nematodes showed reduced incidence as nematodes have an effect of destroying mycelium. Rotation too has an impact on Armillaria infection prevalence. Forests which previously were dominated with conifer and later transited to the deciduous tree, show reduced infection incidences. The occurrence attributed to the fact that the transition leads to increased CO2 capacity as decomposition occurs. CO2 has an inhibition effect on the growth of Armillaria.

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Pests are known to compromise with plant health hence its immunity. Healthy trees rarely get attacked by Armillaria disease. Drying and dying trees were found to be affected, and the infection only came in to speed up the death of trees. Trees infested by bark beetle were the most affected. It is a clear indication that biotic stress increases host susceptibility. The trees earlier affected by armillaria too were found to be susceptible to insects also. It shows that pests and armillaria exhibit dependency on each other.

Since armillaria species can persist in soil for long periods, removal of stumps is necessary. Forests that practiced stump removal showed significantly reduced prevalence compared to those that retained stumps. Replanting time too affects forests replanted after over five years were less affected. The longer time the land is left bear, the higher the chances of getting rid of rhizomorphs and mycelium in the soil.

Armillaria spp., were almost distributed fairy in the game parks. Other influencing factors from tree species were present, for example, rain frequency and density. Sloppy areas with a 20%- 30% sloppiness and oriented towards the west, with acid soils that are highly porous, and mean rainfall of 1800mm per annum were the most favorable conditions for growth and prevalence of Armillaria infections. Deciduous forests and hardwoods are also less affected compared to softwood coniferous species. Host resistance and adaptability play a critical role in disease distribution and prevalence.



Armillaria species have economic importance, and for this reason, its identification is necessary. It is advisable to identify its species right from morphological, biological, up to the genetic level. Two techniques used in the study, namely,  cultural methods, and polymerase chain reaction(PCR), which is the molecular technique. Different species showed different morphology. In this section of the study, the morphology and phylogeny of identified species will be discussed.

Physically, all species exhibited a yellow-brown color on their caps, and these caps had been a bit sticky when touched. From their collection point, they were found to be growing in groups on stumps of up to fifty mushrooms. Caps of mature species had a diameter range of 3 to 15 centimeter. Cap shape differ with age, it starts with the conical shape when young, assumes a convex shape, and later it has a depression at the center. The stipe might or might not have a ring. The species also produce white powdery spores. They have a root-like extension which is called the rhizomorphs. These rhizomorphs are responsible for disease spread from tree to tree.

From DNA sequencing results, 33.38% of the samples were those of A. gallica, 43.49% were those of Armillaria species, 9.1% were those of other fungal species, and 3.3% of other Armillaria species. Amplification was repeated twice for clarity of results. The technique proved to be active and eliminated ambiguity identification of purified cultures. A. gallica exhibited the highest complexity. The delicate annuli and a clavate stipe distinguish it from the rest of the general. Its genetic identification proved hectic as isolates occurred in different loci. The strain for the same species in the tree family appeared to be placed in different and distant positions. There was also minimal statistical nodes support. The species, together with A. cepistipes exhibit polyphylogeny and has cryptic species. The identification I further complicated by the fact that single gene genealogies include more than one biological species. A. ectypa too is presumed to be sisters with A. gallica.

The A.Mallea was the easiest to identify as they had no ring at the stipe, annulus was distinct, and robust basidiocarps. Phylogenetically, they exhibited intraspecific variation at the DNA levels. They also displayed intraspecific differences in their sexual gametes. A. tabascens have no annulus nor ring in on their stipes.  It also exhibited phylogeny variation at the DNA level.

  1. ostoyae, A. borealis were found to contain more similar phylogenetic characteristics compared to other Armillaria species. However, A. ostoyae is monophyletic, and the latter is paraphyletic. The two species are also known for lack of stipe another distinguishing characteristic from the rest of the genera. The only differing parameter is in terms of distribution.

There has been an improvement and more innovation when it comes to DNA sequence and phylogenic techniques. Different new species are still discovered with time. Nevertheless, species boundaries between related taxa have a lot of learning to be done. The species of Armillaria has proved to be confusing in terms of boundaries as they are closely related with minimal distinguishing characteristics. Molecular phylogenies such a random frequency length polymorphism (RFLP), can be employed to solve such puzzles.

For more accurate data concerning loci Genealogical Concordance Phylogenetic Species Recognition (GCPSR), could come handy. The technic is phylogenomics based and has a large number of collection of the transcriptome has I highly promising. The technique is ao cot effective and fast.

Tree species, and Armillaria species existence and distribution.

Different species prefer different hosts. From the collection, distribution, and existence concerning tree species in broadleaf forests were established. Armillaria tabescens had a larger distribution in oak trees compared to other species. A.gilicca also showed dominance, but a significant reduction of number in the mountains was evident in oak tree distribution.  Armillaria mellea occurs displayed more dominance in broadleaved forests more than other species whereas A. ostoyae andA. cepistipes were dominant in highlands and among the conifers. A. ostoyae and A. Cepistipes were also common in deep valleys. In the oak forest, it showed that Armillaria gallica was the weakest pathogen. It is well known as a weak pathogen of oak.

Armillaria gallica was not dominant in healthy trees even though it was actively involved in the death of trees after defoliation.  It can be found on the round but mostly situated in tree stumps. Underlying basic soils were also prone to the species compared to acidic soils. Hence, Söderskog had a higher prevalence. It also Affected less vigorous oak trees.

  1. mellea, on the other hand, infected healthy trees without producing any symptoms, unless other species come in.
  2. mellea is the key pathogen of broadleaf forests. It has the biggest host range compared to other species. C. Japonica, however, exhibited some form of resistance to A. mellea, as it had the least incidence of attack by the pathogen. Pinus spp. Exhibited the highest level of susceptibility as it showed aerial symptoms of aggression. However, it was observed to reduce its incidence in trees in higher altitudes.
  3. tabescens was found to be prevalent in four oak species and hornbeam tree. The four oak species were; Hungarian Oak, Turkey oak, sessile oak, and Mesophillus sessile oak. Armillaria ostoyae was found to be the most virulent affecting beeches, fir, spruce, and pine.


Armillaria species is associated with mot forest deaths though it is not easy to determine their effects. The end of a tree is always influenced by other biotic and abiotic factors such as pests and environmental conditions; Armillaria spp only comes in an opportunist.

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