PHYLUM BASIDIOMYCOTA

Characters of Basidiomycetes (Basidiomycetes is not a class name but the members of phylum Basidiomycota are commonly known as basidiomycetes):

• They produce their sexual spores known as Basidiospores.
• Basidiospores are produced outside of a specialized, microscopic spore producing structure called Basidium.
• Basidiospores of most species are known as ballistospores which are discharged from the basidium forcibly.
• As a result of Karyogamy, Plasmogamy, and meiosis four (4) basidiospores are produced in each basidium. The basidiospores are haploid and may be uninucleate or binucleate at maturity.
• Extensive dikaryophase occurs.
• Mycelium is septate.
• A dolipore septum is present between the two hyphal cells which regulate the flow of particles across the cells.
• There is also the presence of a clamp connection between two hyphal cells that ensures the dikaryotic condition in each new cell of the secondary mycelium.
• Mycelium of most heterothallic basidiomycetes passes through three distinct stages of development before it completes its life-cycle i.e.

1. Primary,
2. Secondary, and
3. Tertiary mycelial stages.

1. Primary mycelium: It develops from germinating basidiospores. These may be uninucleate or multinucleate. But always homokaryotic (all the nuclei are genetically identical).
2. Secondary mycelium: It is produced from primary mycelium. It is dikaryotic and heterokaryotic (Each cell contains two nuclei which are genetically different from each other).
3. Tertiary mycelium: It contains specialized tissues that produce a basidiocarp. On basidiocarp basidia are produced that bear basidiospores.

• On the basis of structure basidium can be divided into two types:

1.  Holobasidium: It is single celled and club shaped, and there is no primary septation.
2. Phragmobasidium: It is typically divided into four cells by the primary septa.

• Basidium is divided into three parts:

1. Probasidium: It is that portion of basidium in which karyogamy takes place.
2. Metabasidium: It is that portion of basidium in which meiosis takes place.
3. Sterigmata: It is any portion of the basidium between the Metabasidium and a basidiospore. So it serves as a connection between basidium and basidiospore.

• Basidia are formed in a definite layer known as hymenium.

Dolipore septum: It is a doughnut like (ring shaped) or barrel shaped swelling in the centre of septal wall surrounding a central pore.

Septal Pore Cap: Dolipore Septum is covered on either side by a dome shaped membranous structure known as Septal Pore Cap.

Clamp Connection: As a result of Spermatization or more commonly the fusion of two uninucleate cells of the compatible, homokaryotic mycelia, a binucleate cell is established (a-b). When this binucleate cell is ready to divide a short bridge like branch which is known as clamp connection arises between two nuclei a & b, and begin to form a hook. The nuclei divide simultaneously, one division occurs in such a way that one daughter nucleus b forms in clamp connection and other b’ forms in dividing cells. The division of other nucleus takes place in such a way that one daughter nucleus a form near one end of cell and the other a’ approaches the nucleus b’ of first division near the other end of cell. In the mean time the clamp has bent over and its free end has fused with the cell, so that the clamp forms a bridge through which one of the daughter nuclei b passes to the other end of the cell and approaches one of the daughter nuclei a of other division. A septum forms to close the clamp at the point of its origin and another septum forms vertically under the bridge to divide the parent cell into two daughter cells with a and b nuclei in one daughter cell and nuclei a’ and b’ in the other. Now we can say that the presence of clamp connection is generally indicative of the dikaryotic condition. 

Nutrition: These are the most widely distributed fungal group of individuals, so as their nutrition. They mostly occur as Rust, Smut, Jelly fungi, Mushrooms, Shelf fungi, Puffballs, Stink horn, and Bird’s nest fungi.

Reproduction: Two types of reproduction:

1. Sexual Reproduction: It takes place by the production of basidiospores. In rust fungi Spermatization also occurs.
2. Asexual Reproduction: It takes place by means of budding, by fragmentation, by the production of conidia and Arthrospores..

Classification:

            Basidiomycetes are divided into three classes namely;

1. Hymenomycetes.
2. Gastromycetes.
3. Ustilaginomycetes.
4. Urediniomycetes.

1. Hymenomycetes: It has eight orders but two of them are important:
   1. Aphyllophorales: These are wood-rotting fungi e.g. Ganoderma, Polyporous.
   2. Agaricales: These include edible mushrooms (Agricus bisporus) as well as poisonous fungi (Amanita phalloides).

Characters:

1. This order includes fungi whose fruiting body is known as mushroom.
2. They include edible and poisonous mushrooms.
3. Chinese, Shiitake, Button, Oyster are different types.
4. Development of Micorrhizal association.
5. Types of Mushrooms:
   1. Gymnocarpous: Those in which Hymenium is exposed while the spores are still immature.
   2. Angiocarpous: Fertile layer is enclosed by basidiocarp until the spores are matured.
6. Agaricales occur in a variety of habitats i.e. on dead leaves (folicolous), on wood (lignocolous), and on dung (corpophilous).

Aphyllopherales:

Characters:

• They include Poly porous, Tooth fungi, Corel’s fungi, Club fungi and Bracket fungi.
• Hymenium is present over the fruiting body and is of two types depending upon their position:

1. Unilateral: If Hymenium is present on one side of the basidiocarp.
2. Amphigenus: If Hymenium is present all over the surface of basidiocarp.

2.Gastromycetes:

Characters:

• There is no Hymenium formation contrary to Hymenomycetes.
• They include Puff balls, Stinkhorn, Earth star, Bird’s nest fungi.
• Fruiting body has two layers:
  1. Outer layer of basidium is known as peridium.
  2. Fertile portion of basidiocarp is enclosed by peridium called as gleba (meaning cloud).

3.Urediniomycetes: It has four orders but one is important:

Uredinales:

 Characters:

1. These are the Rust fungi.
2. The members are obligate parasites.
3. Four basidiospores are produced in each basidium.
4. Basidiospores are forcibly discharged.
5. Clamp connections are not found and binucleate condition is developed by Somatogamy.
6. Sex organs are produced but basidiocarp is not produced.
7. Mycelium is intercellular and food is taken in through haustoria.
8. Rust fungi may produce as many as five different stages in their life-cycles:

          Stage 0              Spermogonia bearing spermatia (n) and receptive hyphae (n).

          Stage 1              Aecia bearing aeciospores (n+n).

          Stage 2              Uredinia bearing urediniospores (n+n).

          Stage 3              Telia bearing teliospores (n+n →2n).

          Stage 4              Basidia bearing basidiospores (n)

1. Based on the Life-cycle pattern species of Uredinales may be divided into three categories:

a       Macrocyclic Forms: These exhibits all the five reproductive stages e.g.    

         Stem rust of wheat (Puccinia graminis f.sp. tritici).

b       Demicyclic Forms: These lacks Stage 2 i.e. Uredinal stage e.g.  Linseed     

         rust (Melampsora lini).

c    Microcyclic Forms: Both aeciospores and urediniospores are absent and

      the teliosopre is the only binucleate spore produced.

Teliospore: A thick walled resting spore of rust and smut fungi in which karyogamy occurs. Also called Teleutospore

1. Depending upon the host two types of fungi:
   1. Autoecious: These complete their life-cycle on a single host species.
   2. Heteroecious: These produce Stages 0 and 1 on one host species called primary host and Stages 2 and 3 on another host Species called alternate host e.g. Barbaris vulgaris. P.graminis. causes stem rust of wheat so wheat is primary host and barberry is alternate host, while Stage 4 is not parasitic.
2. Uredinales order has three families:
   1. Pucciniaceae:

Characters:

• Teliospores are free and do not from a crust.
• Teleutospore form septate mycelium after germination.
• They may be one celled, two celled or many celled.
• Important Genera:
  1. Puccinia→ Bi-celled
  2. Uromyces→ Single-celled
  3. Phragmidium→ Many-celled
• Melampsoraceae:
  • Teliospores are united and form a crust, layers or columns.
  • Teleutospores after germination produce non-septate promycelium
  • Sessile teleutospores are produced.

Taxonomic Status of;

1. Puccinia graminis f.sp. tritci                                Causes: Stem rust of wheat
2. Puccinia graminis f.sp. hordei                            Causes: Stem Rust of Barley
3. Puccinia graminis f.sp. secalis                            Causes: Stem Rust of Rye
4. Puccinia recondita f.sp. tritci                               Causes: Leaf rust of Wheat
5. Puccinia striiformis f.sp. tritci                              Causes: Stripe rust of Wheat
6. Uromyces fabae                                                    Causes: Bean rust
   1. Order: Uredinales
   2. Family: Pucciniaceae
7. Melampsora lini                                                   Causes: Linseed rust
   1. Order: Uredinales
   2. Family: Melampsoraceae

4.Ustilaginomycetes: It has two orders but one of them is important:

1. Ustilaginales:

 Characters:

1. These produce smut and bunt diseases in plants.
2. These are facultative parasites.
3. These produce indefinite no. of basidiospores.
4. Basidiospores are passively discharged.
5.  No sex organs are produced.
6. Hyphae generally grow intercellularly but at some times intracellularly.
7. They also lack haustoria.
8. This order has two families.

• Family Ustilaginaceae: Promycelium is septate and the teliospores are attached on lateral side.
• Family Tillitiaceae: Promycelium is aseptate and the teliospores are attached on terminal portion.

Taxonomic Status of;

1.  Ustilago tritici                                          Causes: Loose smut of wheat
2. Ustilago hordei                                         Causes: Covered smut of Barley
3. Ustilago nuda                                           Causes: Loose smut of Barley
4. Ustilago maydis                                        Causes: Common smut of Maize
5. Ustilago scitaminae                                  Causes: Flag smut of Sugarcane                   
6. Ustilago kolleri                                         Causes: Covered smut of Oat
7. Spacellotheca sorghi                                Causes: Grain smut of Sorghum
8. Spacellotheca reiliana                              Causes: Head smut of Maize
   1. Order: Ustilaginales
   2. Family:Ustilaginaceae
9. Nevossia indica                                         Causes: New bunt of Wheat
10. Nevossia horrida                                      Causes: Bunt of Rice
    1. Order: Ustilaginales
    2. Family: Tillitiaceae