The secret life of Honey fungus

. If someone asks you which is the largest living organism on the Earth? What will be your answer?  African Elephants or Giant Blue Whale? No, let us tell you that, the world’s largest living organism is surprisingly a fungus! Yes, you read it right, Honey Fungus is the correct answer. The name honey fungus is enough to strike fear in a gardener’s mind. Scientifically known as Armillaria solidipes, the honey fungus is one of the most fearful pathogens. For the past 20 years, it is on the top of the RHS Advisory Service pathogen enquiry list. Commonly found in gardens and woodlands throughout Europe and the Oregon region of the United States, the honey fungus causes Armillaria root disease in many plants like Avocado. It is known for killing mature trees and shrubs within a few years.

Fungi: the underestimated kingdom

Fungi emerged as the third kingdom after Monera and Protista, recent studies have revealed that fungi are closely related to the animal and plant kingdom. According to research conducted by scientists, more than 90% of fungal species in the world are not yet scientifically known. We as mycologist explorers know so little about them. Fungi members play various important roles in our lives, for example, some fungus has medicinal properties, some can be used as a source of protein, food, etc., etc. Apart from this, some have fungi are the cause of life-threatening diseases and as they are earth’s best organic matter degraders, they have some other potential effects.

One fungus from the kingdom of fungi is HONEY FUNGUS, scientifically known as Armillaria, which can be seen very commonly but we never heard about it, right? It serves as a parasite on plant roots, killing many trees. You must be wondering how an organism like fungi can be so disastrous? 

Honey fungus: a Gardener’s Nightmare

As mentioned earlier Honey fungus is a common name given to different species of the genus Armillaria, the fungus of this group particularly has yellowish-brown, edible mushrooms. However this fungus also has parasitic nature as it attacks, feed, and kill the roots of perennial plant and trees, it spreads underground attacking and killing plant roots and decaying the wood. Based on the parasitic nature of this fungus, it is also called “a Gardener’s Nightmare”.

Image Source: annualreview.org

Far-fetched facts about honey fungus

• Armillaria solidipes is popularly found in the woods of Oregon, in the U.S. 
• Honey fungus found in the Blue Mountains of Oregon occupies about 2400 acres of land thus contributing to the world’s largest living organism on land.

It is as big as the size of three central parks and its weight is as much as that of 5000 African elephants.

Discovery of Honey Fungus

The research was conducted by the U.S. forest department in 1998 regarding the investigation of the cause of a huge number of tree deaths in the Malheur National Forest in eastern Oregon. They took 112 samples from dead and decayed trees and the research results were surprising as all the collected plant specimens were seen to be infected with the same fungus. It was concluded that Armillaria solidipes covered an area of 3.7 sq miles and about 1900-and 8650 years old.

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It was found that at that time the largest known organism was a fungus from the same genus, but A.solidipes overtook and thus tagged as the “largest living” and the oldest organism with deadly pathogenicity. It was confirmed that  A. solidipes clonal colony was a single organism (this was because of sharing the same genetic makeup and different cells interact with each other as a whole organism system. Other examples-A. mellea and A. gallica

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Mycologists compared the fungus with other similar fungi from the same genus to look up genetic similarities as well as evolutionary relationships. They also compared the rhizomorphs of Honey fungus (root-like structures, often black) with the fruiting bodies. The focus was on the mechanism of killing trees and how it eliminates its competitors which were also wood-decaying fungi and bacteria.

Thallus

The body of the fungus consists of mycelia (in the form of a mat) situated underground and fruiting bodies called mushrooms located above the ground; the hyphae of fungal mycelium draw nutrients out of the host plant roots and thus killing the plants. Mushrooms or fruiting bodies (yellowish-brown) are usually found near the base of infected host trees.

Life cycle

The species is famous for its harmful parasitic nature, causing death and decaying of trees by root rot. An early symptom is the dieback of the crown and branches of affected host trees. We usually observe it producing long, black-coloured, stringy cords, under the bark of the tree. These are also produced in the soil around the roots of the host plant. Most vulnerably affected are injured, young trees.

Image source: 1) www.researchgate.net 2) ucanr.edu

Control

There is no such chemical control to prevent the honey fungus from spreading in an unaffected area.

The only effective remedy to prevent it from spreading once it is confirmed in an area is to dig and destroy the infected patch of the area. The reason for the effectiveness of the same is that once detached they are unable to grow in the soil.

On the other hand, there are some preventive measures one can keep in mind to limit or prevent honey fungus from spreading in unaffected areas. One of them includes putting a physical barrier. For instance, a deep vertical strip of butyl rubber can be used. Another example is a heavy-duty plastic sheet. It can be buried in the soil which will the role to block the rhizomorphs. Deep cultivation if done regularly can be another preventive measure that will break up the rhizomorphs.

Another important preventive measure can be to avoid the most susceptible plants and go for the ones that are rarely infected by Armillaria sp.

Ecological connections

Due to the immobile characteristics of fungus, they were considered plants a long time ago. Today fungi constitute their own kingdom as classified in the five kingdom classification.

Fungus, unlike plants, cannot synthesize their food (HETEROTROPHS), they depend on their host for food. Fungi have their own importance in the ecosystem. However, some fungus plays a vital role in the biosphere. They are essential for recycling nutrients in all habitats as they are dominant decomposers. They decompose compounds such as cellulose and lignin. However, some species like Honey fungus are parasitic. They cause real damage to the ecosystem by destroying forest areas over 3.7 sq miles in size.

Keep reading at MBD for such interesting facts!

Team MBD

Read more- Honey fungus / RHS Gardening