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Current Category » Introductory Plant Pathology

General Characteristics of Fungi

1. Vegetative Thallus:

The body of the fungus is called as Thallus, which is without stem root and leaves. Some fungi may be unicellular yeasts while some fungi may be multi cellular moulds. A single thread like filament is called as hypha. A hypha is made up of a thin, transparent tabular wall filled or lined with a layer of protoplasm.

A group of hypha or network of hyphae constituting the body of fungus is called as mycelium may be septate or aseptate. i.e coenocytic or Nonseptate.

a) Nonseptate or Aseptate or Cornocytic Mycelium:
  
When mycelium is not divided by cross walls called as non septate mycelium.

Depending upon the nature of parasitism with the host plant, mycelium is either ecotophytic or endophytic.

b) Septate Mycelium:

When mycelium is divided by cross walls or septa called as septate mycelium.

i) Ecotophytic Mycelium:

The hyphae grows on external surface or epidermal cells by means of special sucking organs called as haustoria. E.g. Powdery Mildew Fungi.

ii) Endophytic Mycelium:

When hyphae grows inside the epidermal layer of plant or host tissues, is called as endophytic mycelium. E.g. Powdery mildew fungi. Endophytic mycelium is of following types.

a) Intercellular
b) Intracellular
c) Vascular

a) Intercellular Mycelium:

Mycelium growing in between the cells.

b) Intracellular Mycelium:

Mycelium growing within the host cell. E. g Smut Fungi.

c) Vascular Mycelium:

Mycelium growing in vascular tissues of the plant. E. g Wilts.

2. Cell Wall:

Cell wall is well defined, typically chitinised which contains chitin or cellulose or both (Cellulose in oomycetes), living structure of the cell called as organells (Cytoplasm, nucleolus and protoplasm). Nonliving structure of the cell called as Inorganells (Chitin , cellulose).

3. Nutrition:

In fungi, nutrition is heterotrophic i.e. Photosynthesis lacking and absorptive ( They lack chlorophyll and can’t manufacture their own food from CO2 and water). Their mechanism of nourishment is absorption which takes place by osmosis through the cell walls.

Fungi are divided into three groups according to the manner they obtain their food as:

1. Saprobes,
2. Symbionts,
3. Parasites or hyper parasites

1. Saprobes or Saprophytes:

Those organism which requires dead organic matter to complete its life cycle as saprophytes. E.g. Mucor and Rhizophus.

2. Symbionts or Symbiosis:

When two dissimilar organisms lives together in close association for mutual benefits is called as symbiosis. When two or more organisms lives together in close association for two or more organisms lives together in close association for mutual benefits is called as mutualism.

E.g. lichen-Fungus and algae Mycorrhiza- Fungi and roots of higher forest plants

3. Parasites:

An organism which obtain its food from living tissues of plans or animals is called as parasite.

Or

An organism which completely depends on its host for food called as parasite.

Among the parasite one can distinguish different degree of parasitism as i) Obligate parasites ii) Non obligate parasites, iii) Facultative saprophytes iv) Facultative parasites.

i) Obligate Parasites or Biotrophs:

Those organisms which requires living hosts or tissues complete their life cycle , are called as obligate parasites. They can never be grown on dead, artificial food material. Rust, mildews, viruses.

ii) Non Obligate Parasites or Necrotrophs:

Those organisms when kills the tissue in advance of penetration and then lives on it as saprophytically. E.g. Sclerotium rolfsii, Claviceps, Ventruria.

iii) Facultative Saprophytes:

These are the organisms which are usually parasites in their mode of life but under certain conditions they become saprophytes. E. g. Smut, Sphacelotheca sp.

iv) Facultative Parasites:

These are the organisms which are usually saprophytic in their mode of life but under certain conditions they become parasites. E.g. Pythium, Phytophthora.

4. Nuclear Status:

Eukaryotic multinucleate, mycelium being homocakaryotic or heterokaryotic or haploid or diploid or dikarytoic limited duration. Well defined structures i.e. nuclear membrane, nucleolus, and chromatin material.

5. Sexuality:

Sexual or asexual and homo or heterothallic.

6. Life Cycle:

Simple to Complex.

7. Sporocarps:

Microscopic or macroscopic and showing limited differentiation.

8. Distribution:

Cosmopolitan.

Current Category » Introductory Plant Pathology