Fungi: Negative Impacts, Diseases, and Decomposition

Fungal Negative Relationships: Biodeterioration

• Saprotrophic fungi can contaminate food or destroy manufactured consumer goods from raw materials.
• Fungal damage can cause significant losses of stored, moist food.
• Some saprotrophic fungi produce dangerous metabolites called mycotoxins in seeds and grains.

Fungi as Saprobes and Decomposers

• Fungi act as Saprobes and Decomposers

Crop/Plant and Animal Diseases

• Fungi cause most plant diseases and several animal diseases, including those in humans.

Crop Diseases

• Fungal parasites can be used in biocontrol, but have possible negative effects on crop production.
• Plants are highly susceptible to molds and fungi's threat to agriculture, leading to crop losses when untreated.
• Common crop diseases caused by molds and fungi include:
  • Blight of potato and rice
  • Rust of wheat
  • Smut of corn, sugarcane, wheat, and barley
  • Green ear disease of bajara
  • Downy mildew of pea
  • Tikka disease of groundnuts

Examples of Plant Pathogens

• Alternaria triticina causes leaf blight in wheat.
• Fusarium oxysporum f. sp. lycopersici causes Fusarium wilt in tomatoes.
• Rhizoctonia solani causes sheath blight in rice.
• Sclerotium rolfsii causes wilt in potatoes.
• Alternaria solani causes early blight in tomatoes and potatoes.
• Alternaria alternate f. sp. lycopersici causes early blight in tomatoes.
• Ceratocystis paradoxa causes pineapple disease in sugarcane.
• Phytophthora infestans causes late blight in potatoes.

Fungi as Plant Pathogens

• Gungi frequently attack crops

Animal Diseases

• A wide variety of fungi live harmlessly on and in humans.
• Pathogenic fungi are the primary cause of fungal infections, resulting in poisoning and allergies or hypersensitivity.
• Fungi also cause systemic fungal infections like candidiasis and aspergillosis.

Lichens

• Lichens consists of an alga/phycobiont (phycos = alga, bios - life), and a fungus/mycobiont (mykes = fungus, bios = life).
• Lichens are living in symbiosis.
• The fungal partner typically makes up most of the lichen’s structure and creates reproductive parts.
• The algal component uses photosynthesis to make food and the fungal absorbs.

Characteristics of Lichens

• Lichens are composite plants of thalloid nature that include algae and fungi.
• The algal partner provides carbohydrates via photosynthesis for both organisms.
• The fungal partner absorbs and retains water.
• Thallus morphology includes crustose (flat), foliose (leafy), and fruticose (shrubby) forms.
• Lichens reproduce vegetatively, asexually, and sexually.

Lichen Reproduction

• Lichens reproduce vegetatively through fragmentation, decaying older parts, soredia, and isidia.
• Lichens reproduce asexually via oidia formation.
• Lichens reproduce sexually through ascospore or basidiospore formation. Only the fungal component is involved.

Ascospores and sex organs

• Ascospores are produced in Ascolichens.
• The male sex organ, spermogonium, is flask-shaped and produces spermatia.
• The fruit body morphology includes apothecial (disc-shaped) and perithecial (flask-shaped) types.
• Asci develop within the fruit body, containing eight ascospores, which germinate and form new lichens when they contact suitable algae.
• Basidiospores are produced in Basidiolichens, resembling bracket fungi on the fruit body's lower side.
• Lichen growth is slow, and survival occurs in high temperatures with dry conditions.

Lichens: Habitats and Growth

• Lichens consist of 400 genera and 15,000 species worldwide.
• Their thalloid bodies generally grow on bark, leaves, dead logs, and bare rocks in varied habitats.
• Lichens thrive in less polluted forest areas with ample moisture.
• Cladonia rangiferina (reindeer moss) populates Arctic and Antarctic regions.
• Lichens grow abundantly in the Eastern Himalayas but not in polluted industrial zones.
• Lichens are grouped by growing region:
  • Corticoles grow on tree bark in sub-tropical/tropical regions.
  • Saxicoles grow on rocks in cold climates.

Lichen Symbiotic Relationship

• The composite plant body of lichens consists of algal and fungal members.
• Algal members are in Chlorophyceae, Xanthophyceae and Cyanobacteria.
• Fungal members are mainly in Ascomycotina with some in Basidiomycotina.

Lichen Associations

• One view is that the fungus lives parasitically.
  • Haustoria from parasitic fungus hyphae penetrate and absorb nutrients from algal cells.
  • Isolated algae can survive independently, but fungi cannot.
• Another view suggests a symbiotic relationship.
  • The fungus absorbs water and minerals and protects algae.
  • The algae synthesizes organic food for both partners.
• The alternative third view is that the fungus dominates.
  • The algal partner is subordinate, similar to helotism (master & slave relationship).

Lichen Classification

• Lichens are classified by the fungal partner's fruit bodies rather than any system.
• Zahl Bruckner classified lichens into Ascolichens and Basidiolichens.
• Ascolichens have a fungal member belonging to Ascomycotina.
  • Gynocarpeae series have disc-shaped (apothecial) fruit bodies known as Discolichen like Parmelia.
  • Pyrenocarpeae series have flask-shaped (perithecial) structures and are known as Pyrenolichen like Dermatocarport.
• Basidiolichens contain fungal members belong to Basidiomycotina like Dictyonema or Corella.

Lichen types

• Basidiolichen: Fungal partner is Basidiomycetes like Dictyonema.
• Deuterolichen: Fungal partner is Deuteromycetes.
• Ascolichen: Fungal partner belongs to Ascomycetes like Parmelia, Cetraria.

Importance of Lichens

• Lichens are useful and harmful to mankind, and are sources of food, fodder, medicine and sources for industrial uses.

Lichens as Food and Fodder

• Lichens are consumed by both humans and animals such as snails, slugs, termites, etc. containing polysaccharide, lichenin, cellulose, vitamin, and certain enzymes. -Parmelia is used as curry powder in India. -Endocarpon miniatum is a vegetable in Japan. -Evernia prunastri is for making bread in Egypt. -Cetraria islandica (Iceland moss) is a food in Iceland.
• Ramalina species are used as animal fodder.

Lichens in Medicine

• Lichens contain lichenin and other substances and being used medicinally since pre-Christian times.
• Lichens are used to treat jaundice, diarrhea, fevers, epilepsy, hydrophobia, and skin diseases.
• Cetraria islandica and Lobaria pulmonaria are used for tuberculosis and other lung diseases.
• Parmelia species can be used for epilepsy.
• Lichens help in antiseptic creams.

Lichens; Industrial uses

• Lichens have various industrial applications.
• Lobaria pulmonaria and Cetraria islandica are used in tanning leather.
• Lobaria pulmonaria is also used in brewing beer.
• In Russia and Sweden, Usnea florida, Cladonia rangiferina, and Ramalina fraxinea are used in the production of alcohol due to the lichenin.

Lichens and Dyes

• Lichens have been used to dye fabrics since pre-Christian times. Dyes can be brown, red, purple, or blue.
• Brown dye uses Parmelia omphalodes to dye wool and silk.
• Red and purple dyes are available in Ochrolechia androgyna and O. tartaria.
• Cetraria islandica's blue Orchil dye is used for dyeing woolens.
• Orcein is used in laboratories and coir dyeing.
• Litmus, is extracted from Roccella tinctoria, R. montagnei, and Lasallia pustulata.

Lichens in cosmetics

• Aromatic compounds, along with essential oils extracted from Ramalina and Evernia species, are used in soaps.
• Ramalina calicaris is used to whiten wigs and species of Usnea retain scent.
• Evernia prunastri and Pseudevernia furfuracea are used widely in perfumes.

Ecological Importance of Lichens

• Lichens are pioneer colonizers on dry bare rocks.
  • Crustose lichens colonize with luxuriant growth when there are minimum nutrients and water.
  • Lichens secrete acids helping decompose the rocks.
• Death of lichen mixes with the rock particles, and forms a thin layer of soil which aids plants.
• In plant succession, lichens grow first, then mosses, then vascular plants.

Lichens as pollution indicators

• Lichens absorb Radioactive Substances purifying the atmosphere.
• Cladonia rangiferina (reindeer moss) and Cetraria islandica (Iceland moss) exist in the Tundra region.
• Lichens are very sensitive to pollutants like SO2, CO, CO2 and are used as Pollution indicators.
• Crustose lichens tolerate pollution more than other types of lichens.