Ecological Groups of Fungi Lecture Notes PDF

Ecological Groups of Fungi  Fungi are heterotrophic organisms. The modes of heterotrophic life in fungi are categorized into: 1. Saprobic: living at the expense of dead organic matter. 2. Parasitic: living at the expense of another host organism (algae, plants, fungi, animals); Bi...

Ecological Groups of Fungi  Fungi are heterotrophic organisms. The modes of heterotrophic life in fungi are categorized into: 1. Saprobic: living at the expense of dead organic matter. 2. Parasitic: living at the expense of another host organism (algae, plants, fungi, animals); Biotrophic if the host is colonized while fully alive. Necrotrophic if the host is first killed and then fully colonized. 3. Symbiotic: a mutual relationship that benefits both the fungus and its partner(s). 1:Symbionts and Endophytes Fungi living on the exterior of their hosts are called epiphytes. Those living within host tissue, which are termed endophytes. A: Endophytes: can protect host plants from insect herbivory and from other fungal pathogens  used as bioregulators to induce resistance against diseases.  biological control agents against certain pathogens and undesirable weeds.  Methods for isolation 1:Tissue pieces are sterilized using the following protocol: 60 s in 70% ethanol 2-5 min in NaOCl (1-3 %; depending on tissue type) and again 60 s in 70% ethanol (to remove the NaCOl). 2: Tissue samples are plated on PDA amended with streptomycin (1 mL/L) and incubated at 25 ᵒC. 3: Emerging fungal colonies must be hyphal-tipped, and transferred to PDA slants for further identification. B: Symbionts Lichens Lichen is a beneficial mutualistic association between a fungus and an alga. Mycobiont: the fungal partner in lichen. Photobiont: the photosynthetic partner in a lichen; either a green alga or cyanobacterium. Characters of Lichens Worldwide distribution, often in the most extreme environments, Arctic, Antarctic, deserts and all other habitats. Occur on soil, plants, animals, rocks, decorate tombstones, buildings, etc. Rare in polluted areas - intolerant of industrial pollutants, especially sulfur dioxide. Mycobiont usually takes up about 90% of the thallus and is usually an ascomycete (most are inoperculate discomycetes) or occasionally a basidiomycete (eg. Omphalina, Multiclavula). Photobiont may be a green alga, cyanobacterium or both. Both the algae and cyanobacteria fix carbon and the cyanobacteria fix nitrogen. Advantages to the alga: Mechanical protection from injury & high light by being tightly enveloped by hyphae. Improved water relations and resistance to desiccation. Provides minerals. Advantages to the fungus: Organic nutrients (carbon & nitrogen) provided by photobiont. Lichenized fungi have greater longevity. Most lichenized fungi are never found free- living in nature. Structure of lichens – Cortex (upper and/or lower). – Medulla (fungal layer). – Algal layer. Types of lichens: Stratified lichen: algal cells are not distributed through lichen. Non Stratified lichen: algal cells are distributed through Uses of Lichens Food Dyes Essential oils for perfumes, soaps Bioactive compounds (antiviral, antibacterial) Nesting/bedding material Poisons  Reproduction of Lichens: Sexual spores (ascospores & basidiospores). Conidia Mycorrhizae Definition Types Functions  Symbiotic association between a fungus & the root of vascular plants. The roots of 95% of all kinds of vascular plants are involved in mycorrhizae. It's believed that the symbiotic association of plant roots & fungi led to our modern vascular plant.  Types of mycorrhizae 1-Ectomycorrhizae 2-ectendomycorrhizae 3-endomycorrhizae Arbuscular mycorrhizae(AM) Ericoid endomycorrhizae Orchid endomycorrhizae  1-Ectomycorrhizae form a sheath (covering the root tip) the fungus grows between the plants cell producing the harting net (extensive network of intercellular hyphae between epidermal& cortical cells) Septate fungi ( Ascomycetes )  2-Ectendomycorrhizae different from Ectomycorrhizae in that some hyphae actually penetrate into the root cells Septate fungi ( Basidomycetes )  3-Endomycorrhizae A) Arbuscular mycorrhizae (AM) the hyphae enter the plant cells, producing vesicles(which are swollen spherical or (oval) structures or arbuscules (finely dichotomously branching hyphae invaginations) ; to increase surface area between hyphae & cytoplasm of the cell where nutrients exchange (major site of nutrient exchange between fungus and plant) Non-septate fungi ( zygomycota )  B)Ericoid endomycorrhizae the fungus penetrate the plant cells. consisting of dense coils of hyphae in the root cells. Septate fungi. (Ascomycetes ) Ericoids : “are trees such as tea & blue berry”.  C) Orchid endomycorrhizae Hyphae penetrate cells of embryo & form coils called pelctons. Septate fungi (Basidomycetes ) Orchid : “plants which produce flowers like orchids & vanilla (flowering monocot plants)”.  Functions of mycorrhizae :- Mycorrhizae can increase the plant's competitiveness depending on the environment of the plant improving plant growth. Wet environment :- they increase the availability of nutrients , especially phosphate Arid environment:-The mycorrhizae aid in water uptake, allowing the increase in transpiration rate in comparison with non-mycorrhizal plants Mycorrhization Helper Bacteria These are symbiotic bacteria trapped within Mycorrhizal of fungi they can found in cytoplasm of Ectomycorrhizae and also Arbuscular mycorrhizea. Bacteria play a role in the development of the Mycorrhizal relationships. The main function of bacterial symbionts in ectomycorrizal fungus is that these trapped bacteria contribute to the (N) metabolism by assisting with the synthesis of essential amino acid.