Q.5. How a dikaryotic cell of Basidiomycotina divides to produce new cell? (2007)
Related Question -
Q. Write a note on clamp-connection. (2010, 12)
Ans. Most of the Basidiomycetes are heterothallic i.e. the primary mycelium in them is of two distinct strains which are called + and - strain. The formation of the secondary mycelium involves the interaction between two compatible primary mycelia. Two compatible hyphae (+ and - strain) from the neighbouring Mycelia meet. The intervening walls between the two adjacent cells at the point of contact dissolve. The protoplasts of the uninucleate cells termingle in the fusion cell. The two nuclei in the fusion cell do not fuse. The binucleate cell thus formed is known as the dikaryotised cell. The dikaryotic cell divides repeatedly by conjugate divisions to give rise to a dikaryotic mycelium. During the nuclear divisions of the dikaryotic cell special structure called the clamp connections are formed.
Clamp Connection:-
When the dikaryotic cell (A) is ready to divide a pouch - like outgrowth arises from its wall (B), it arises midway between the two nuclei of the dikaryon. The two closely associated nuclei of the cell now divide simultaneously. One of four daughter nuclei, generally the lower one of the upper pair, passes into the pouch (C). A septum appears at the base of the pouch (D). As a result the pouch is cut off from the main cell. It may be now called a clamp cell. The clamp cell grows into hook like structure. Its tip bends over and finally fuses with the lateral wall (E) of the parent cell. The clamp cell now forms a bridge. It is called the clamp connection. Another septum is laid down vertically under the bridge usually at about the level of the upper end of the clamp connection (E) It divides the parent cell into two daughter cells.
The terminal daughter cell has two nuclei. Each of these is a sister nucleus of the parent dikaryon. The lower or basal daughter cell possesses
one nucleus. The fourth nucleus of the clamp connection now migrates into the basal daughter cell. The latter also becomes binucleate (F). The clamp connections are usually formed on the terminal cells of the hyphae of the secondary mycelium . Thus, by this process new cells are formed continuously.
Puccinia
Q.1. Write about life history of Puccinia graminis or Rust disease of wheat.
Related Questions -
Q. With the help suitable diagrams explain the life cycle of Puccinia graminis in detail. (2003)
Q. Which is called as heteroecious fungus? Write the name of any polymorphic fungus and in brief mention the different kinds of spores found in sexual reproduction. (2006, 13)
Q. What is heteroecious fungus? Write the name of any polymyorphic fungus and also name different types of spores produced in completion of its life cycle. (2008)
Q. What is Heterocism? Describe the stages of Puccinia Graminis on Wheat. (2011)
Ans. Systematic Position: -
Kingdom - Mycota
Division - Eumycotina
Sub-division - Basidiomycotina
Class - Teliomycetes
Order - Uredinales
Family - Pucciniaceae
monokaryotic in some stages, while it is dikaryotic in other stages.
The mycelium is provided with knob-like or fingershaped haustoria which enter the host cells and absorb food materials. The monokaryotic mycelium of Puccinia is found on barberry and dikaryotic mycelium on wheat plants. Puccinia is a obligate fungus. Puccinia completed its life - cycle on two hosts.
When a rust parasite passes some stages of its life cycle on one host and remaining stages on other host, this condition is called heteroecious and this phenomenon is called as heterocism the fungus is called as heteroecious fungus, e.g., Puccinia graminis passes some stages on wheat and some on barberry plants. P. graminis (black rust) is a wide spread rust of cereals which affects wheat, oat, barely, rye and numerous wild grasses and produces brown rust or black rust. It is a macrocyclic rust.
Symptoms: -
Symptoms of this disease produce in the form of rusty coloured spots on aerial parts of plants.
Fig. Puccinia - Wheat stem showing black streaks and symptoms of disease on Barberry leaf.
Life cycle:-
The life history of Puccinia graminis is divided into 5 stages which are based on the nature of the spores. It is a heteroecious fungus. It completes life cycle on two hosts. These are wheat and barberry. The life cycle of Puccinia consists of following type of spores:
(i) Uredospores (on wheat plant)
(ii) Telutospores (on wheat plant)
(iii) Basidiospores (onbarberry leaf)
(iv) Pycnidiospores (on barberry leaf)
(v) Acidiospores (on wheat plant)
(i) Uredospores:-
In the plants of wheat infection appears in February or March when vertically elongate reddish brown and black, pustules appear on stem or leaf. These pustules are called uredosori containing uredospores. Each uredospore consists of two nuclei and cytoplasm. The outer brownish wall is expospore sand inner endospore. On maturation of uredospores the epidermis of host bursts and they are liberated in air. Infavourable condition they germinate and from germ tubes which infect healthy plants. Thus the rust disease get spread.
Fig. puccinia - (A) Teleutospores in sorus, (B) Structure of teleutospores
(C) Germination of teleutospores and formation of basidiospores
(ii) Teleutospore: - In April, uredia begin to produce teleutospore. A pustule of teleutospore is called teleutosorus or telium and appear as black colord streaks. Teleutospore is bicelled and spindle shaped. It is covered with exospore and endospore wall.
(iii) Basidisopore:-
Diploid teleutospores geminate into a hyphae branch called promycelium and produce new type of spores, called basidiopores. Basidiospore are small, unicellular uninucleate haploid and hetesrothallic in nature as two of them represent (+) and other two (-) strain.
(iv) Pycnidiospores:-
Each basidiospore on germination forms a monokaryotic mycelium. Since this fungus is heterothallic the basidiospore are either of (+) or (-) strain. After few days mycelium (+ or -) produces pycnidia and pycnidial or spermogonia. These are flask shaped and mouth is called ostiole. Pycnidiospore is circular and oval thin walled structure. Pycnidiospore produces spermatia. A number of longer cylindrical and unbranched or slightly branched flexuous hyphae with blunt tips which arises beneath and among the paraphysis. These are respective hyphae or flexuous hyphae and represent the female sex organs and pycnidiospores as male sex organs.
(v) Aecidiospores:-
Aecidial cup produces aecidiospores. These spores develop on the lower epidermis and opposite to pycnidial spores. A few sporophores emerge from dikaryotic hyphae which forms a chain of binucleate dikaryotic spores called aecidospores.
Disease Cycle:-
In the plains of India uredospore works as primary inoculam. These spores spread by wind from hills to plain and after maturity produce teleutospores. Teleutospores germinate and produce a promycelium which is diploid in nature. After meiosis of promycelium or epibasidium and haploid nuclei are formed in which two strain are (+) and (-). Each basidium cell produces haploid basidiospores. These basidiospores spread by wind and infect the barberry plant and germinate by germtube which enters in plant tissues and produces intercellular mycelium.Opposite to pycnidospores the aecidiospores are formed in aecidial cups on lower epidermis of barberry leaf. Aecidiospores produce spermatia on maturity spermatia (+ or -) which reached on respective hyphae (+ or -) by insects and pairing of opposite nucleus occurs and nucleus become diploid. Basidium produces acidial cup and these cup produce spermatia. The spermatia are diploid and form aecidium spores. These aecidium spores are thin walled, unicellular, diploid in nature. The spore infect wheat plants and germinate to produces dikaryotic mycelium. This mycelium produces dikaryotic unicellular, one celled uredospores. So this is a complete life cycle of P. graminis.
Method of control of black rust: -
(1) By growing rust resistant varities.
(2) By Avoid excessive use of Nitrogenous manure.
(3) By destruction of barberry bushes.
(4) Dusting spraying of sulphur compounds.
(5) Destruction of infected wheat plant to avoid its spread.