Adventist Youth Honors Answer Book/Nature/Fungi

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Fungi
Nature
General Conference
Skill Level 2 Answer-Keys 06.jpg
Year of Introduction: 1937

1. Give the name of five classes of fungi and examples of each.[edit]

Chytridiomycota
The phylum Chytridiomycota, the chytrids, represents a group of primitive aquatic fungi. They are characterized by having reproductive cells can move themselves by using whip-like tails called flagella. Synchytrium endobioticum is a chytrid fungus that causes the potato wart disease or black Scab.
Zygomycota
The zygomycetes, in phylum Zygomycota, are characterized by the formation of sexual spores called zygospores. The zygospores are not contained within a specialized fruiting body or sac. An example of a zygomycete is the common black bread mold, Rhizopus nigricans.
Glomeromycota
Members of the Glomeromycota are also known as the arbuscular mycorhizal fungi. Only one species has been observed forming zygospores; all other species only reproduce asexually.
Ascomycota
The ascomycetes are members of the phylum Ascomycota. They are also called the “sac fungi” because their sexual spores (ascospores) are enclosed in tube-like sacs known as asci. Familiar examples of sac fungi include morels, truffles, Baker's yeast, Dead Man's Fingers, cup fungi, and the majority of lichens (loosely termed "ascolichens") such as Cladonia.
Basidiomycota
Basidiomycetes, also known as the “club fungi,” are classified in phylum Basidiomycota. Basidiomycetes include some of the most complex fungi, including mushrooms and puffballs.

2. Identify fifteen common fungi of your locality. Draw or photograph them from live specimens.[edit]

The best way to approach this requirement is to go out looking for fungi, and then try to figure out what you have found. This is far more effective than studying your field guide, deciding what you want to look for, and then going out for a look.

To do this, you will need a field guide. The field guide you select should cover the area where you are looking for mushrooms. For example, a field guide to the mushrooms of Australia is not going to help you very much if you're looking for fungi in North America.

Once you have a field guide, take it, plus your camera or sketch pad, and go out looking for fungi. When you find one, try to figure out what it is using your field guide. It is difficult to distinguish the various species of fungi from photographs alone, so you will want to identify it on the spot. Many times the identification of a species will rely on an obscure feature such as the gills on the underside of a mushroom. Chances are, if you attempt to identify the fungus later from a snapshot, you will not have captured one of the critical identifying features, or the feature was not sufficiently in focus. That is why you will want to make an identification when you have direct access to the specimen. If you find yourself looking at an interesting specimen and do not have your field guide with you, by all means, sketch it out and take photos. There is always the chance that you will be able to identify it later. Take special notice of the gills (if there are any), how they attach to the stem, and any "fringes" around the stem.

3. Name three important fungi and tell what their value is.[edit]

Saccharomyces cerevisiae
This fungus is used in baker's yeast.
Aspergillus niger
This fungus is used to make citric acid commercially, and it also can be used to make gluconic acid. Both are important food additives.
Penicillium chrysogenum
This is the organism that makes penicillin, from which the majority of the large class of beta-lactam antibiotics are derived. Penicillin and its derivatives have saved countless lives since they were discovered and isolated, starting in the 1940s.

4. Tell the life history of one example of each of the following:[edit]

a. Rust[edit]

Rust infection

Rust occurs on many species of plant, but in most cases any one species of rust can only infect one species of plant. The following describes the infection process of asexual spores.

Spore Attachment

When a rust spore lands on a plant surface it needs to attach to it, or it would simply be washed off. First, weak, hydrophobic interactions are formed between the spore and the plant cell surface. Then unknown signals cause the production of a substance called adhesin. This will stick the spore irreversibly to the plant surface. Once attached, the spore will germinate.

Germ Tube Elongation

Rust fungi penetrate the plant by using the natural pores on the underside of a leaf, but first the growing germ tube must locate it. The germ tube grows in a random manner until it reaches a ridge. At this point it will start to grow perpendicular to the ridge, greatly increasing its chances of locating a pore (called a stomata).

Appresorium Formation

The stomata is the site of a structure called an appresorium that functions to both firmly anchor the fungus and aid in penetration. From the appresorium an infection peg grows down into the plant and between the leaf cells.

The Haustoria

Rust fungi gain their nutrients from living cells. This requires a specialized penetration of the fungi into a living plant cell called a haustoria. This develops from a haustorial mother cell. The plant cell membrane surrounds the main haustorial body. An iron- and phosphorus-rich neck band bridges the plant and fungal membranes and acts as a seal preventing the escape of nutrients into the plant. The rust fungi will then continue to grow and invade the plant until it is ready to make new spores.

b. Mold[edit]

Penicillium chrysogenum is a mold that is widely distributed in nature, and is often found living on foods and in indoor environments. It is the source of several β-lactam antibiotics, most significantly penicillin.

Like the many other species of the genus Penicillium, P. chrysogenum reproduces by forming dry chains of spores (or conidia) from brush-shaped stalks called conidiophores. The conidia are typically carried by air currents to new colonization sites. In P. chrysogenum the conidia are blue to blue-green, and the mold sometimes exudes a yellow pigment. However, P. chrysogenum cannot be identified based on color alone. Observations of morphology and microscopic features are needed to confirm its identity.

c. Mushroom[edit]

Nidulariaceae - Bird's nest fungi

Bird's nest fungi are fungi with fruiting bodies that look like egg-filled birds' nests and make up the order the Nidulariales.

They are often seen on decaying wood and in soils enriched with wood chips or bark mulch. Cyathus striatus is probably the most commonly encountered species in the temperate northern hemisphere.

The "eggs" are spore cases called peridioles. Peridioles contain glebal tissue, basidia (a microscopic, spore-producing structure), and basidiospores (a reproductive spore), and are dispersed by rain. The nests are splash cups. When a raindrop hits one at the right angle the walls are shaped such that the eggs are expelled a good distance from the nest. Each egg has a sticky trailing thread attached to it. If that thread encounters a twig on its flight the egg will swing around and wrap itself around the twig. The spores can then germinate there and start the life cycle over again.

d. Yeast[edit]

The yeast cell's life cycle.
1. Budding
2. Conjugation
3. Spore

Yeasts have asexual and sexual reproductive cycles; however the most common mode of vegetative growth in yeast is asexual reproduction by budding or fission. Here a small bud, or daughter cell, is formed on the parent cell. The nucleus of the parent cell splits into a daughter nucleus and migrates into the daughter cell. The bud continues to grow until it separates from the parent cell, forming a new cell. The bud can develop on different parts of the parent cell depending on the genus of the yeast.

Under high stress conditions haploid cells will generally die, however under the same conditions diploid cells (cells containing a full set of chromosomes) can undergo sporulation, entering sexual reproduction (meiosis) and producing a variety of haploid spores (which have only a half-set of chromosomes), which can go on to mate (conjugate), reforming the diploid.

5. Identify five fungus plant diseases.[edit]

Fusarium oxysporum[edit]

Fusarium oxysporum, also referred to as Agent Green, is a fungus that causes Fusarium wilt disease in more than a hundred species of plants. It does so by colonizing the water-conducting vessels (xylem) of the plant. As a result of this blockage and breakdown of xylem, symptoms appear in plants such as leaf wilting, yellowing and eventually plant death.

Interest in Fusarium oxysporum as a pesticide was first raised after the discovery in the 1960s that it was the causative agent in the destruction of the Hawaiian coca population.

The United States government was involved in a controversial program to use Fusarium oxysporum for the eradication of coca in Colombia and other Andean countries, but these plans were cancelled by president Bill Clinton who was concerned that the unilateral use of a biological agent would be perceived by the rest of the world as biological warfare. The Andean nations have since banned its use throughout the region. Use of biological agents to kill crops is potentially illegal under the Biological Weapons Convention.

Downy mildew[edit]

Downy mildew (left) and Powdery mildew (right)

Downy mildew refers to any of several types of oomycete that infect plants. In commercial agriculture, they are a particular problem for growers of crucifers, grapes and vine-type vegetables.

The prime example is Peronospora farinosaas featured in NCBI-Taxonomy and HYP3.

Cucurbit downy mildew (caused by Pseudoperonospora cubensis) is specific to cantaloupe, cucumber, pumpkin, squash, watermelon and other members of the gourd family. The disease is one of the most important diseases of cucurbits worldwide.

Botrytis (Leaf blight, Neck rot)[edit]

Botrytis

Botryotinia is a genus of ascomycete fungi causing several plant diseases. The anamorphs (asexual reproductive stage) of Botryotinia are mostly included in the imperfect fungi genus Botrytis. The genus contains 22 species and one hybrid.

Plant diseases caused by Botryotinia species appear primarily as blossom blights and fruit rots but also as leaf spots and bulb rots in the field and in stored products. The fungi induce host-cell death resulting in progressive decay of infected plant tissue, whence they take nutrients.

Alternaria alternata[edit]

Alternaria alternata

Alternaria alternata has been recorded infecting over 380 host species. It is opportunistic pathogen on numerous hosts causing leaf spots, rots and blights on many plant parts. It also causes upper respiratory tract infections in AIDS patients and asthma in people with sensitivity.

Smut[edit]

Corn smut

The smuts are fungi, mostly Ustilaginomycetes (of the class Teliomycetae, subphylum Basidiomycota), that cause plant disease.

Smuts affect grasses, notably including cereal crops such as maize. They initially attack the plant's reproductive system, forming galls which darken and burst, releasing fungal spores which infect other plants nearby.

A smut infestation is controlled by removing and destroying the infected plants. In Agriculture, this process is known as destruction of the initial inoculum.

There are several types of smut including:

Magnaporthe grisea[edit]

Lesions on rice leaves caused by infection with M. grisea

Magnaporthe grisea, also commonly known as rice blast fungus, rice rotten neck, rice seedling blight, blast of rice, oval leaf spot of graminea, pitting disease, ryegrass blast, and johnson spot, is a plant-pathogenic fungus that causes an important disease affecting rice. It can also infect a number of other agriculturally important cereals including wheat, rye, barley, and pearl millet causing diseases called blast disease or blight disease. M. grisea causes economically significant crop losses annually, each year it is estimated to destroy enough rice to feed more than 60 million people. The fungus is known to occur in 85 countries worldwide.

6. Know what safety precautions to observe when handling fungi.[edit]

Flood conditions contribute to the growth and transmission of many kinds of fungi, some of which can cause sickness. Cleanup workers are at increased risk of exposure to airborne fungi and their spores because they often handle moldy building materials, decaying vegetable matter, rotting waste material, and other fungus-contaminated debris. The fungal material is carried into the respiratory tract when airborne particles are inhaled.

There are many different kinds of fungi, including mildew, molds, rusts, and yeasts. Most of these are harmless, but some can cause respiratory and other disorders when workers inhale or come into contact with fungi. Inhalation is the route of exposure of most concern to flood cleanup workers. The recommendations below offer strategies for workers renovating flooded buildings, homes, and structures to protect themselves while handling building materials that are visibly contaminated with fungi.

For workers cleaning up flooded buildings, homes, and other structures, excessive moisture or water accumulation indoors will encourage the growth of the fungi that are already present. Some fungi have the potential to cause adverse health effects such as allergic responses and asthma attacks. Individuals who are sensitive to molds may have signs and symptoms of allergic reactions such as nasal stuffiness, eye irritation, and wheezing. These individuals should minimize fungal exposure by wearing respirators, gloves, and eye protection. They should also seek to eliminate fungi, as described below. In addition, repeated or prolonged contact of the skin with flood water and continuous sweating can lead to fungal skin infections. These can be minimized or avoided by washing the skin with warm, soapy water and keeping it as dry as possible.

If a person experiences severe allergic or skin symptoms, or severe flu-like symptoms, he or she should seek medical advice. A health care provider can determine whether medication or any other precautions are necessary.

Tips to Remember[edit]

For anyone who may be exposed to mold and fungi:

  • Avoid breathing dust (fungal spores) generated by moldy building materials, crops, and other materials.
  • Consider using a disposable respirator as a minimum when working with moldy or damp hay, grain, compost, or building materials.
  • Consider discarding all water damaged materials. Articles that are visibly contaminated with mold should be discarded. When in doubt, throw it out.
  • Surfaces that have a light covering of mold should be scrubbed with warm, soapy water and rinsed with a disinfectant made of 1/2 cup liquid household bleach mixed into one gallon of water.
  • CAUTION: Do not mix bleach with other cleaning products that contain ammonia.
  • After working with mold-contaminated materials, wash thoroughly, including the hair, scalp, and nails.
  • If the safety of food or beverage is questionable, throw it out. Only drink safe drinking

water that has been bottled, boiled, or treated until there is confirmation that the community water supply is safe for consumption.


For additional information concerning fungi, health effects, and addressing flood damaged materials, please visit OSHA’s Safety and Health Topics web page on Molds and Fungi at: http://www.osha.gov/SLTC/molds/index.html

References[edit]