Nutritional mode of Fungi / Parasitic fungi

Parasitic fungi attack living organisms, penetrate their outer defenses, invade them, and obtain nourishment from living cytoplasm, thereby causing disease and sometimes death of the host.

Most pathogenic (disease-causing) fungi are parasites of plants. Most parasites enter the host through a natural opening, such as a stoma (microscopic air pore) in a leaf, a lenticel (small opening through bark) in a stem, a broken plant hair or a hair socket in a fruit, or a wound in the plant.
Among the most common and widespread diseases of plants caused by fungi are the various downy mildews (e.g., of grape, onion, tobacco), the powdery mildews (e.g., of grape, cherry, apple, peach, rose, lilac), the smuts (e.g., of corn, wheat, onion), the rusts (e.g., of wheat, oats, beans, asparagus, snapdragon, hollyhock), apple scab, brown rot of stone fruits, and various leaf spots, blights, and wilts.
These diseases cause great damage annually throughout the world, destroying many crops and other sources of food.

For example, nearly all the chestnut forests of the United States have been destroyed by the chestnut blight fungus (Cryphonectria parasitica), and the elms in both the United States and Europe have been devastated by Ophiostoma ulmi, the fungus that causes Dutch elm disease.
These diseases cause great damage annually throughout the world, destroying many crops and other sources of food.

For example, nearly all the chestnut forests of the United States have been destroyed by the chestnut blight fungus (Cryphonectria parasitica), and the elms in both the United States and Europe have been devastated by Ophiostoma ulmi, the fungus that causes Dutch elm disease.
These diseases cause great damage annually throughout the world, destroying many crops and other sources of food.

For example, nearly all the chestnut forests of the United States have been destroyed by the chestnut blight fungus (Cryphonectria parasitica), and the elms in both the United States and Europe have been devastated by Ophiostoma ulmi, the fungus that causes Dutch elm disease.
These diseases cause great damage annually throughout the world, destroying many crops and other sources of food.

For example, nearly all the chestnut forests of the United States have been destroyed by the chestnut blight fungus (Cryphonectria parasitica), and the elms in both the United States and Europe have been devastated by Ophiostoma ulmi, the fungus that causes Dutch elm disease.

1. Parasitic Fungi Parasitic fungi attack living organisms, penetrate their outer defenses, invade them, and obtain nourishment from living  cytoplasm , thereby causing disease and sometimes death of the host. Most pathogenic (disease-causing) fungi are  parasites  of plants. Most parasites enter the host through a natural opening, such as a stoma (microscopic  air  pore) in a  leaf , a lenticel (small opening through bark) in a  stem , a broken  plant  hair or a hair socket in a fruit, or a wound in the plant. Fig : Pathogenic (disease-causing) fungi

2. Parasitic Fungi Among the most common and widespread diseases of plants caused by fungi are the various  downy mildews  (e.g., of grape, onion, tobacco), the powdery mildews  (e.g., of grape, cherry, apple,  peach , rose, lilac), the smuts  (e.g., of  corn , wheat, onion), the rusts  (e.g., of wheat, oats, beans, asparagus, snapdragon, hollyhock),  apple scab , brown rot of stone fruits, and various leaf spots,  blights , and  wilts . Fig : Rusts

3. Parasitic Fungi These diseases cause great damage annually throughout the world, destroying many crops and other sources of food. For example, nearly all the  chestnut  forests of the  United States  have been destroyed by the  chestnut blight  fungus ( Cryphonectria parasitica ), and the  elms  in both the United States and  Europe  have been devastated by  Ophiostoma ulmi , the fungus that causes  Dutch elm disease .

4. Parasitic Fungi Infection of a plant takes place when the spores of a pathogenic fungus fall on the leaves or the stem of a  susceptible  host and germinate, each  spore  producing a germ tube. The tube grows on the surface of the host until it finds an opening; then the tube enters the host, puts out branches between the cells of the host, and forms a mycelial network within the invaded tissue. The germ tubes of some fungi produce special pressing organs called  appressoria, from which a microscopic, needlelike peg presses against and punctures the  epidermis  of the host; after penetration, a  mycelium  develops in the usual manner. Fig : Appressoria

5. Parasitic Fungi Many parasitic fungi absorb food from the host cells through the hyphal walls appressed against the cell walls of the host’s internal tissues. Others produce  haustoria  (special absorbing structures) that branch off from the intercellular hyphae and penetrate the cells themselves. Fig : Haustoria of Funji

6. Parasitic Fungi Haustoria, which may be short, bulbous protrusions or large branched systems filling the whole cell, are characteristically produced by  obligate  (i.e., invariably parasitic) parasites; some facultative (i.e., occasionally parasitic) parasites also produce them. Obligate parasites , which require living cytoplasm and have extremely specialized nutritional requirements, are exceptionally difficult, and often impossible, to grow in a  culture  dish in a laboratory. Examples of obligate parasites are the downy mildews, the powdery mildews, and the rusts.

7. Parasitic Fungi Certain fungi form highly specialized parasitic relationships with  insects . For example, the fungal genus  Septobasidium  is parasitic on  scale insects  (order  Homoptera ) that feed on trees. The mycelium forms elaborate structures over colonies of insects feeding on the  bark . Each insect sinks its proboscis (tubular sucking organ) into the bark and remains there the rest of its life, sucking sap. The fungus sinks  haustoria  into the bodies of some of the insects and feeds on them without killing them. The parasitized insects are, however, rendered  sterile . Fig : Fungal genus  Septobasidium Fig : Fungal genus  Septobasidium

8. Parasitic Fungi The perpetuation of the insect species and the spread of the fungus are accomplished by the uninfected members of the  colony , which are protected from enemies by the fungus body. Newly hatched scale insects crawl over the surface of the fungus, which is at that time sporulating. Fungal spores adhere to the young insects and germinate. As the young insects settle down in a new place on the bark to begin feeding, they establish new fungal colonies. Thus, part of the insect colony is sacrificed to the fungus as food in return for the fungal protection provided for the rest of the insects. The insect is parasitic on the tree and the fungus is parasitic on the insect, but the tree is the ultimate victim. Fig : Scale insects crawl over the surface of the fungus

9. Parasitic Fungi The  sooty molds   constitute  another interesting ecological group of fungi that are associated with insects. The majority of sooty molds are tropical or subtropical, but some species occur in the temperate zones. All sooty molds are  epiphytic  (i.e., they grow on the surfaces of other plants), but only in areas where scale insects are present. The fungi parasitize neither the plants nor the insects but rather obtain their nourishment exclusively from the honeydew secretions of the scale insects. Fig : sooty molds Fig : sooty molds

10. Parasitic Fungi Growth of the dark mycelium over the plant leaves, however, is often so dense as to significantly reduce the intensity of the light that reaches the leaf surface; this reduction in turn significantly reduces the rate of  photosynthesis . Insect-fungus as Fig : sociations found in the tropical forests of Central and South America include the unique relationship of  leafcutter ants  (sometimes called parasol ants) with fungi in the family  Lepiotaceae (phylum  Basidiomycota ). The ants  cultivate  the fungi in their nests as an ongoing food supply and secrete  enzymes  that stimulate or suppress the growth of the fungi. Fig : Insect-fungus associations found in the tropical forests of Central and South America Fig : Unique Relationship Of  Leafcutter Ants