Tag: Fungus

An Underground Kingdom

 

Mycorrhizal fungi are almost entirely underground, with only their fruiting bodies – mushrooms – appearing briefly above ground to sporulate and then disappear. We may think the mushrooms are the most notable part of the Kingdom of Fungi, but that would be like thinking there is little to consider about plants other than their flowers and fruits. It turns out the underground parts of many plants – their roots – could hardly survive without the symbiotic relationship they have developed over 450 million years with the mycelium of mycorrhizal fungi.

 

The mycelium is made up of numerous filaments called hyphae, and it is the hyphae that interact with plant roots to facilitate the plant’s uptake of water and mineral nutrients, for which in return the hyphae receive sugar and carbohydrates from the plant’s roots. Unlike plants, fungi cannot produce their own food. Mycorrhizal fungi secure food through this mutually beneficial exchange with plants. This has been known for quite some time. But there is something else going on that scientists only recently discovered, something they call the Wood Wide Web.

Habichtspilz-Sarcodon-imbricatus
Scaly Hedgehog mushrooms, Sarcodon imbricatus, found in coniferous woods in the district of Eggingen in the city of Ulm in southern Germany. Photo by H. Krisp.

Mycorrhizal network
Mycorrhizal fungi are in a symbiotic relationship with autotrophic plants. The relationship is usually mutually beneficial, the fungus providing the plant with water and minerals from the soil and the plant providing the fungus with photosynthesis products. Some fungi are parasitic, however, taking from plants without providing benefits. Conversely, some mixotrophic plants connect with mycorrhizal fungi to obtain photosynthesis products from other plants. Finally, saprotrophic fungi live on dead organic matter without establishing a symbiosis with plants. Illustration and explanation by Charlotte Roy and Salsero35.

An underground network of connected mycelia and roots can span thousands of acres, and through it plants such as trees can send chemical signals to other trees. In effect the trees in a forest can be said to be communicating with each other through their underground social network, facilitated by miles upon miles of mycorrhizal fungi mycelia and hyphae. It is not unlike the system of pipes of varying diameter underlying a city, where some pipes deliver water or water-borne materials, while others carry communications between the inhabitants above ground.


“The Wood Wide Web”, a segment of the PBS NOVA web series Gross Science, produced and presented by Anna Rothschild.

Are the trees sentient? Are mushrooms aware of their part in the bigger picture during their brief look around above ground before they produce spores and collapse back into the fecund earth? Of course not. But assemble all the parts, adding pieces as in a jigsaw puzzle, and it does indeed seem the Earth itself is a living thing called Gaia. This awareness, lost to us for centuries, is now returning dimly, though it was always there for those prepared to observe carefully the natural world, such as how a plant wrenched from its native soil and potted with great attention to its needs still rarely thrived as it would have had it been allowed to stay at home. The newly potted plant receives all it requires in water and mineral nutrients; yet in isolating the plant from its underground social network can it be said, perhaps only fancifully, to be lonely?
— Izzy

 

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The Top Banana

 

Since the loss of most of the Gros Michel, or Big Mike, banana plantations due to a destructive root rot by the middle of the twentieth century, the Cavendish has taken over as the most productive banana variety worldwide. By all accounts the Gros Michel was a more flavorful variety than the Cavendish, but growers who wanted to continue producing on a vast scale for the international market had no choice but to switch after fungus reduced the productivity of Gros Michel to an uneconomical level. Now the Cavendish faces similar destruction from another strain of the same fungus, and agronomists are scrambling to find a replacement for the Cavendish.

The Cavendish banana, like the Gros Michel, is a clone. One plant of Cavendish is exactly like the next plant of Cavendish. Such a monoculture is extremely susceptible to pest and disease problems because it cannot adapt through genetic accidents brought about by sexual reproduction. It’s a stationary target. Growers could turn to the extraordinary variety of other, sexually reproduced bananas, and they do just that locally in the tropical areas of the world where bananas grow. The problem for growers who sell internationally has always been finding disease and pest resistant varieties that would hold up under less than ideal shipping conditions and still be economically viable on a large scale.

The first in a series of animated commercials produced by the United Fruit Company in the 1940s for display in movie theaters. The singer was Monica Lewis.
Bananas naturally contain numerous large, hard seeds, making eating them a challenge. It is easier to comprehend the relationship of bananas to berries when confronted with all those seeds. Besides being unavoidable to banana eaters, the seeds were also viable. Modern commercial varieties like the Cavendish have been bred to have seeds that are barely noticeable, turning those varieties into convenience foods. Peel, eat, and don’t worry about the seeds. In the process of hybridizing banana varieties for less inconvenient seeds, agronomists also rendered the seeds unviable. The Cavendish, like the Gros Michel before it, reproduces only exact replicas of itself from parts of an existing plant, without benefit of differing input from any close relatives.


Reliably predictable results are great news for economic giants in any sphere, and agriculture is no exception. The American agribusinesses United Fruit and Standard Fruit, which eventually morphed into Chiquita and Dole, respectively, built themselves into indomitable international forces largely on the predictability of first the Gros Michel and then the Cavendish. They became enormously powerful, vertically integrated corporations that controlled the internal politics of many Latin American countries – the so-called banana republics – and pulled the strings of the United States’ foreign policy. All so that people in wealthy, temperate zone countries could enjoy a fruit that grew only in the tropics.

Banano costa rica (1)
It is possible to buy bananas in the U.S. that have been grown in a more ethically sound and environmentally friendly manner than those produced by the huge international companies, but expect to pay a premium. Photo by Axxis10.

Unlike the spice trade, which also dealt in commodities that mostly grew in the tropics, bananas were and are a superfluous item in the diets of people outside the tropics. Spices were valued in the days before refrigeration on account of their utility in preserving other foods or making them more palatable. Bananas are high in potassium, an essential mineral, but so are potatoes and beans, both of which grow well in temperate zones, as well as being available for winter eating due to their good storage qualities. Bananas sold in temperate zone countries are luxury items available at affordable prices due to the ability of powerful international corporations to exploit cheap labor in tropical countries for growing a dependable crop capable of surviving shipment halfway around the world and arriving in salable condition.

The economic model developed by United Fruit and Standard Fruit in the early twentieth century has been copied and adapted ever since by growers and shippers of other produce, from grapes to mangoes, available now in temperate zone countries even in the middle of winter. As nice as it would be for large international banana producers to abandon monoculture with its reliance on pesticides and fungicides, only to have to abandon that one variety when its production is no longer economically sustainable, they may have no other choice if they want to continue with business as usual. It’s in the nature of their economic model. Locally sustainable small scale agricultural production would of course apply to bananas consumed in the tropics, as it always has, but not in colder countries, where they do not grow.

For all the convenience in the past century and more of being able to pick up a bunch of bananas at the grocer’s in countries where the average person would be more likely to see sub-tropical citrus fruit orchards than tropical banana plantations, not everyone enjoys bananas, or at least not the texture of actual bananas. They may like banana flavor, but they don’t care for the texture, which can be mushy and sticky, activating their gag reflex. For those people, the absence of bananas from the grocer’s would not be a painful loss. Certainly they would still like to have overripe bananas to use in banana bread and other delicious recipes. But unlike the supposedly fresh bananas for eating out of hand, bananas for cooking don’t have to look perfect. In that case, imperfect is just fine.
― Izzy

The last scene of Billy Wilder’s 1959 comedy Some Like It Hot, with Joe E. Brown and Jack Lemmon.

 

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The Pigeon and the Chestnut

 

Scientists are attempting to bring the Passenger Pigeon, Ectopistes migratorius, back to life from preserved genetic material. The Passenger Pigeon once numbered up to 3 billion in North America, but by 1914 the last one had died at the Cincinnati Zoo. Scientists are also working on reviving the nearly extinct American Chestnut, Castanea dentata, which had once totaled over 3 billion trees in North America before a bark fungus accidentally imported from Asia with some Chinese Chestnuts, Castanea mollissima, destroyed almost all of the trees in the first half of the twentieth century.
Male Passenger Pigeon
Male Passenger Pigeon; digital painting by Tim Hough.
PSM V84 D563 American chestnut central maryland
American Chestnut tree in central Maryland in 1914; photo by United States Forest Service.
The loss or near loss of both these species greatly changed the ecosystem of eastern North America to the point that a visitor time traveling from the nineteenth century would be hard pressed to recognize it as the same place, never mind all the modern infrastructure of concrete, steel, and asphalt. Both species were casualties of the first stages of globalization. The Passenger Pigeons had co-existed with Native Americans for millennia, but it was the mass immigration of Europeans which eventually drove them to extinction through habitat loss and hunting on a massive scale. The American Chestnuts had no immunity to the fungus which arrived with the shipment of Chinese Chestnuts, which had developed some immunity due to having evolved with the fungus in their native habitat.

 

Now scientists are attempting to restore these two species once so numerous that they helped define the environment of eastern North America. Both restorations will require the expertise of geneticists, along with help from ornithologists and botanists, as appropriate. Ultimately the success of both projects will depend on the cooperation of the public by giving both species space and peace, two things that humans struggle to allow for the other beings sharing this planet. People were responsible for the demise of both the Passenger Pigeon and the American Chestnut, and with the ingenuity people are known for perhaps they can restore both species. Successful restoration will also require two things people have not often enough been known for, which are a generosity of spirit towards life and restraint of their violently destructive impulses.
― Vita

 

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Careful with that Axe (at last)

There is no time of year when you absolutely should not prune trees and shrubs, particularly when it comes to pruning for the safety of people and property or for the health of the plant. There are better and worse times, however, to paraphrase Charles Dickens from the beginning of “A Tale of Two Cities.”

BLM Botany 03 (6871307185)
Photo by Flickr user Albert Herring

Late summer and early fall is the worst time to prune, and late winter and early spring is the best time. The reason for leaving trees and shrubs alone from August through October (the timing changes depending on the first frost date where you live) is that during frost-free weather pruning encourages new growth, yet the first frost is not far off. If the plant puts out tender new growth at this time of year, a frost may damage or kill the new growth, wasting the the energy the plant just put into top growth at a time when it should be drawing its energy toward its roots in preparation for winter dormancy.

For most trees and shrubs, February through April is the best time for pruning because the plant is dormant, yet it will break dormancy soon and the flush of energy to its top growth will help heal the pruning cuts and cover them. There are exceptions to this rule, and a maple tree is one. Any maple tree produces copious sap in late winter and early spring, not just the sugar maple from which we derive maple syrup. Wounding – and yes, a pruning cut can amount to just that – a maple at that time of year results in excessive bleeding of sap, weakening it. It is better to prune a maple in the summer, when the sap does not run as freely.

Proper pruning technique is necessary in allowing a tree or shrub to to heal a cut. Do not leave stubs! A plant cannot close over a stub, and the stub eventually dies yet remains on the living plant for an inordinate time. The stub then becomes a route for insects and fungi to the interior of the plant. Pruning to the branch collar on trees and to a bud on shrubs allows the plant to seal a cut much sooner, diminishing the opportunity for pests to infest live wood.

Boston Public Garden, Massachusetts (493480) (10791064435)
Boston Public Garden, Massachusetts; photo by Flickr user Robert Linsdell.

Shearing is a form of pruning that makes cuts willy-nilly as far as the plant is concerned, but which to people presents the plant at a uniform shape and size, the effect of which is a matter of personal taste and opinion. At no time is shearing a boon to a plant’s health, though some plants, such as boxwood and privet, are better able to tolerate it than others. The cumulative effects of this detrimental practice are evident after several years as the plant ends up with leaves growing on its outer shell only and no leaves growing inside of that, and the outer shell becomes stiff as the branches thicken. The interior clogs over time with leaves and twigs falling from the shears, allowing fungus to grow and eventually degrade the bark. The remedy for shearing is patience to make pruning cuts by hand in the proper place as far as the plant is concerned, rather than clipping it for the sake of neatness as if a living plant was inert like hair. But as always in our culture, patience is in short supply.

– Izzy 

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