Tag: Roots

The Plant Destroyer

 

The plant pathogen genus Phytophthora, a water mold with similarities to a fungus, is a worldwide threat to ornamental and commercially valuable plants due to how it can develop undetected in the early stages of an infestation. While there are some species of Phytophthora that begin an infestation on the above ground portion of a plant, a much larger portion of the approximately 170 known species of the pathogen start out destroying a plant from within its roots. Phytophthora moves upward from the roots through the water channels of the plant, interfering with the plant’s ability to absorb water as it goes. The effect makes the plant appear drought-stricken, which is essentially the case.

 

One of the plants heavily afflicted by Phytophthora in the past 30 plus years has been the cocoa tree, Theobroma cacao, and specifically the cocoa trees planted in western Africa, where most of the world’s cocoa beans are produced. The species of Phytophthora doing the most damage in that period has been Phytophthora megakarya, a disease that blackens the pods which contain the cocoa beans, rendering most of them unfit for consumption. This disease and a virus transmitted by mealybugs called cacao swollen shoot virus (CSSV) in combination have decimated cocoa tree plantations in western Africa in recent decades.

Plant Disease Triangle
A Venn diagram showing the combination necessary for disease to form. This can apply to humans and animals as well as to plants. Illustration by Earlycj5.

Phytophthora megakarya was introduced from the Americas, where it had long co-existed with the native cocoa trees. The cultivated cocoa trees of western Africa had developed for generations without having to cope with infestations from megakarya, though they had long been contending with Phytophthora palmivora, a less devastating disease for them.

CSSV was native to the forest trees of western Africa, where it did little damage because of long term co-evolution of the trees with the virus. The introduced cocoa trees had no inherited defense against CSSV, resulting in afflicted cocoa trees losing vigor and dying within a few years. Meanwhile, the ants that farmed the mealybugs for their sugary secretions have ensured they continue to live safe from predators by guarding them, even building shelters for them.

Chocolate has grown steadily more expensive, at a rate beyond ordinary inflation, due primarily to shortages of cocoa beans caused by these pathogens. Another reason for chocolate price increases has been related to the salutary shift away from indentured labor on cocoa plantations, making the price more accurately reflect the true cost of production. The cost of production is bound to catch up with any resource as nature asserts itself in one way or another, or in many ways, and imagining that we are immune or insulated from the effects of that assertion is mere hubris and folly. Ultimately, we will pay the price.
— Izzy

 

Nature , , , , , , , , , , , , , , , , , , , , , , , ,

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

 

Soil , , , , , , , , , , , , , , , , , , , , , , , , , , , , ,

The Root of the Matter

 

Growing ginger (Zingiber officinale) is not all that difficult in most parts of the United States as long as the grower understands that except in the warmest zones of the country, ginger is unlikely to produce mature rhizomes. Ginger has a nearly year long growing season, and in three fourths of the country that means it will only produce baby ginger rhizomes even with assistance from the grower to keep the plant warm at the beginning and the end of the growing season. Baby ginger is catching on in culinary circles, however, where it can be used to lighter effect than the full grown type.

Ginger plants
Ginger plants (Zingiber officinale). Photo by Ramjchandran.

The portion of a ginger plant generally used in cooking and medicine is the rhizome, which is technically an underground stem, but to most people it appears to be a tuber or root, and for practical purposes it makes little difference to them what that part of the plant is called. Like a potato, the ginger rhizome has eyes which are starting points for new growth and indicate to gardeners where to divide the rhizome when propagating the plant. Cut up the rhizome with one eye to each section and then plant the sections. In cases where a gardener is concerned with growing only enough ginger for home consumption, the simplest method of planting is one section of rhizome each to wide, shallow pots, which the gardener can move easily from indoors to outdoors and then back again over the course of the 8 or 9 month growing season.

Why go to even that much trouble for a non-native, tropical plant? There is after all a distant relative that is native to North America, known as wild ginger (Asarum canadense), which Native Americans had used in the past as a spice and a medicine, much like its Asian relative. The difference is that scientists have determined American wild ginger can be poisonous, while Asian ginger is safe to consume. In addition to its salutary effect in food and drink recipes, many people believe Asian ginger has anti-inflammatory, anti-arthritic, and anti-nausea properties. Scientists have not necessarily agreed with all those assessments, though they recognize that in the amounts typically consumed by most people there is no harm to eating ginger spiced foods or imbibing ginger infused drinks.

Asarum canadense 03
Wild ginger plants (Asarum canadense). Photo by Michael Wolf.

Djindjipe
A ginger (Zingiber officinale) rhizome on a Delft blue European porcelain plate. Photo by Lucyin.

Of all the South Asian and East Indies spices that are well known to Europeans from earliest trading days, only ginger rewards the gardener who attempts growing it outside its native region or outside tropical climate zones without resort to expensive greenhouses. Start it indoors in late winter on a sunny windowsill and keep it there until mid-spring, when it should be safe to move it outdoors, but always with an eye toward nighttime temperature dips. In the fall, bring the potted plants back indoors and start harvesting baby ginger to last the winter while enjoying the beauty of an unusual houseplant with a tropical feel and a warm, spicy scent.
— Izzy

 

Plants , , , , , , , , , , , , , , , , , ,

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 

Gardening , , , , , , , , , , , , , , , , , , ,