Armillaria mellea, a silent killer

The fungus Armillaria mellea is a serious problem in arboriculture, it kills large numbers of trees in both orchards and in afforestation. It all begins with a spore in the wind. If on a small wound in the bark of a tree base sensitive, germinates and begins the nightmare. The germinating spore gives rise to a white mycelium that grows like a web beneath the bark and feeds on the cambium under bark. In its growth has a predilection for roots and respects the bark and branches, ie, attacks the underground parts of the tree.

Mushrooms of Armillaria mellea in November growing on the roots of a tree in the farm Monnaber of the Serra de Tramuntana in Mallorca. (Double click on the picture to enlarge) 

The mycelium continues to grow from the base of the tree towards the main roots, then secondary and finally the finest. If the road is with a root of another tree encroaches too sensitive, so progress to involve large tracts of land, going from tree to tree like an oil slick. It could be called silent killer because it is not, but there is underground killing thousands of trees, shrubs and lianas. 

Armillaria mellea mushrooms tender in November growing on the root surface of a tree in a mixed forest of pines, oaks and olive trees of the Coll de Soller in Mallorca. This image explains why it was given the name "mellea", ie the color of honey. The tender mushrooms hat is covered with darker scales, which fall off as it grows.

The mycelium of a single individual can come to invade several acres, calculated in tonnes total weight of a single fungus. During the summer heat and drought keep it in aestivation, waiting patiently for the first autumn rains. When the land returns to be wet and temperatures are cooler, restart your nourished invasive activity of the cambium of all that live roots in its path. When you have accumulated enough nutrients, in November or December, laden mushrooms produce spores to reproduce. 

Armillaria mellea in December to grow at the base of an apricot. The color of mushrooms varies by plant parasites, ranging from olive, beige, brown or reddish. 

Previous mushroom close-up views. The hat is between 4 and 12 cms. in diameter and is somewhat darker in the center. The shoots of apricot tree was still alive. In late winter, just when it started to sprout and flourish, died struck with the half-open flowers, as their roots could not feed the buds. 

A previous mushrooms seen by the bottom. The foot is very fibrous and slightly darker than the rest of the mushroom. It is appreciated membranous ring around the foot at its closest to the hat. The mushroom gives off a pleasant aroma. 

 

Armillaria mellea blades decurrent unequal. Its color darkens as they age. Among the films are developed basidium type sporangia, each of which produce 4 spores white, elliptical, maximum diameter no greater than 9 microns. Sporulation is abundant and covered with a white cloth hats that are below. (Double click on the photo to enlarge)

Base of previous apricot mushrooms aside. Emission is abundant rubber as a reaction to the aggression of the fungus. The rubber stops the upward growth of the mycelium, but can not prevent that attack the roots. 

Base of a plum killed by Armillaria mellea. You see the white mycelium under the bark off a strong pungent smell is very characteristic and unpleasant. Plum struck died after spring bud break. 

Armillaria mellea mushrooms growing on the stump of an old rose that killed a year earlier.

Base of a stalk of banana garden, Musa "Orinoco", killed by the stroke of Armillaria mellea mycelium. 

Cross section of stem above completely invaded by the mycelium, which in this herbaceous plant adopts a different arrangement to woody plants. 

Base of the trunk of a Cherimoya, Annona cherimolia, killed by Armillaria mellea. It looks great as the mycelium fails to grow up, while it grows down, invading the cortex of the base of the tree and all roots. You can see the bark still alive in the aerial part of the trunk, and struck the tree died by not receiving water and nutrients that dead roots could not provide. 

Base of the trunk of a mango, Mangifera indica, killed by Armillaria mellea. The tree was 8 years old and had given several abundant crops of fruit. It was very well adapted to the climate of the Valley of Soller, but could not overcome the relentless attack of the fungus. In the picture you see white mycelium after starting a piece of bark. On the right you can also see an infected root. 

Intensely white mycelium handle base above. The smell is so strong and characteristic that once smelled never be forgotten. (Double click on the photo to enlarge) 

Fortunately not all plants succumb to attack by this silent killer, because few have learned to be respected and have gained strength in the form of toxins or antibodies that prevent invasion or destroy the mycelium after they have been attacked. Usually native plants that, after living for millions of years with Armillaria have been adaptive mutations that protect them from fungal attack by fungal toxin synthesis.  

Other plants, although not native, they are able to fight back in the early stages of invasion and destroying fitoanticuerpos produce mycelium. These champions of survival languish for years without even die, the fungus produces mushrooms at the base for three or four autumns, until a spring sprout vigorously, survive the disease and stop producing mushrooms. This dramatic recovery I've seen in avocados, figs, Cryptomeria, palm of fortune, elders, loquat, etc ... 

I had a fig tree "Coll de Dama Negra" I was so upset that for several years gave very few figs, which ripen well, they looked appetizing, but tasted nasty to rot. The leaves were small, yellowish, and in small numbers. Each fall out a good bunch of Armillaria mellea mushrooms at the base of the trunk. One spring there was a miracle and came out big sheets with unusual vigor, in late summer gave a large crop of figs taste great and no more mushrooms out again at its base. It has been 15 years and the fig tree is huge and fully recovered. 

Loquat recovered from the attack by Armillaria mellea. The mycelium was to rot the roots and trunk base. However roots survived emitting sound directly from the bark of the trunk, which have not been attacked by the mycelium which clearly persists in the field and at the rotten roots. In the picture looks very good the rotting remains of the base of the trunk and aerial roots that emerged almost a 10 cms. soil and introduced into the earth to save the tree. The effort had to do was titanic medlar, having no more than a little water and nutrients stored in its trunk and branches dying, which he used with great wisdom to take the aerial roots and saved from certain death. Currently produces large crops of sweet, juicy fruits and appearance is excellent.

Base completely rotten trunk of a willow tree, Sambucus nigra, which also survived a vicious attack of Armillaria. After the sprouting spring began to wilt, leaves turn yellow and fell off in the middle of July. Luckily a few weeks later, in August, it rained for several days and this was what enabled him to survive. Concentrating all the little water and nutrients that he still had in the trunk white rootlets issued directly from the healthy bark, which were introduced recently in the ground moist and miraculously his body in September issued new outbreaks, fed by roots issued. The mycelium of the subsoil and could not attack because the elder had learned his lesson and had synthesized fitoanticuerpos against mycelium. Had autovaccine. 

Despite the apparent evil of Armillaria mellea, it is known that some forest trees that grow in areas infested with the mycelium, not only are not attacked by the fungus, but have learned to benefit from each other in an incredible symbiosis, acting Armillaria as a mycorrhiza. 


Fight this silent killer is totally ineffective. There is no point starting the infected trees, burn their trunks and roots, plowing, treating the soil with fungicides, biological methods used to fight enemies of Armillaria microorganisms entering the field and attack the mycelium. 


Apparently all these methods at first seem to work, but the vast mycelium of several tons, which occupies the ground as a giant underground and invisible web that reaches to cover several acres, is always the best cards to win the game. Cleverly hidden under the protective bark of infested roots or spores remain dormant for years without germinating. Once the danger has passed, when fungicides and have become inactive by oxidation or chemical neutralization or when biological control organisms have died from lack of food (her, its mycelium), then reviving like the phoenix and again do what he does best: killing all plants survive unprotected to be put forward. 


So bad and cunning is the honey mushroom.