Basidiomycotina
Q.1. Define Basidiomycotina and describe the characteristic features of class Basidiomycetes. (2010)
Ans. Subdivision Basidiomycotina is a large group of fungi and is commonly called as Basidiomycetes. The members of this group produce basidiospores exogenously on basidium.
Characteristics features of class basidoimycetes: -
(1) Members of this class usually found on soil, in logs and on tree stumps, may be found as parasites saprophytes.
(2) Plant body is filamentous and septate.
(3) Cell wall of is chitin.
(4) The produce basidiospores on the outside of a specialized spore producing body the basidium.
(5) Basidiospores are uninucleate and haploid.
(6) Presence of clamp connections. e.g., Puccinia, Ustilago Agaricus.
[Ustilago]
(Loose smut of wheat)
Q.1. Give an account of structure and reproduction of Ustilago.
Related Questions -
Q. Write in brief the different types of process of diploidization in Ustilago. (2007, 13)
Q. Describe the systematic position and important characters of Ustilago. (2005, 06, 08, 10, 13)
Q. Describe the life cycle of Ustilago with the help of diagrams only.
Q. Explain Dekaryotization.
Ans. Division - Eumycota
Sub-division - Basidiomycotina
Class - Teliomycetes
Order - Ustilaginalles
Family - Ustilaginaceae
Genus - Ustilago
Characteristics:-
The plant body of the fungus is mycelial. The mycelium is eucarpic, septate and branched. It produces two types of mycelia during it’s 1ife - cycle i.e., primary and secondary.
Primary mycelium is formed by the germination of basidiospores. The mycelium so formed is monokaryotic consisting of slender, hyaline and septate hyphae. It may belong to +ve or -ve strain. Secondary mycelium is dikaryotic, septate. It is not obligate parasite like rusts. It is autoecious fungus means it completed its life - cycle on single host.
Important Species: -
Some of the common species of Ustilago are as follows -
U. tritici : loose smuts of wheat
U. maydis : corn smuts
U. avenae loose smut of oats
U. hordei : covered smut of barley
U. cynodontis : loose smut of doob grass
U. scitaminea : whip smut of sugarcane
U. hypodytis : stem smuts of grasses
Common Symptoms of Smuts: -
Grains or the inflorescence transform in black powdery mass, Except the awns and the central spikelet axis the inflorescence are completely destroyed. The infected plants are reduced in size. Smut disease are of two types
Loose Smuts: -
In case of loose smuts the spores are not covered by any membranous structure. They are directly exposed to the air at the time of flowering and at maturity they are easily dessiminated by wind, e.g. ,loose smut of wheat and oat.
Covered Smuts:-
The spores remain enclosed in a membranous covering of the grains, i.e. they are not directly exposed to the air. The mature spore are therefore not easily disseminated by wind. They are liberated only by the breaking up of the wall of grain, e.g. ,covered smut of barley and sugarcane.
Mycelium :-The mycelium is branched, septate, intercellular, hyaline and usually inconspicuous. According to the nuclear behaviour the nucleus passes through two distinct stages -
(a) Primary Mycelium:-
Primary mycelium is produced by the germination of a basidiospore. It consists of a slender hyaline, septate hyphae. Each cell of mycelium contains a single haploid nucleus. Based on the strain of the basidiospore, the Primary mycelium is either of plus or of minus strains. The Primary mycelium is less extensively developed and is also called haplomycelium or monokaryotic mycelium. The primary mycelium soon changes into secondary mycelium.
(b) Secondary Mycelium:-
It contains two haploid nuclei in each cell. It consists of septate, extensively branched, intercellular hyphae. This mycelium that is usually found in the host. The secondary mycelium is also called dikaryotic.
Process of Diplodization or Dikaryotization:-
The process by which the primary mycelium changes into a secondary mycelium is called diplodization or dikaryotization. In this process two haploid cells of opposite strains copulate to form a binucleate cell. These two nuclei of such cells do not fuse in the vegetative phase and constitute a dikaryon. In Ustilago, diplodization may taken place by any of the following methods-
1. By somatogamy between the hyphae of the primary mycelia belonging to the conidia of the opposite strains, e.g., U maydis.
2. By conjugation between the germs tubes of two gesrminating basidiospores, e.g., U. anthearum.
3. By fusion of a basidiospore of one strain and the germ tube of a basidiospore belonging to the another strains.
4. By the fusion of two basidia formed by the germination of tiliospores of opposite strains, e.g. U. nuda.
5. By the fusion of two adjacent haploid cells of the same epibasidium, e.g., U. hordei.
6. By the fusion of a basidiospore and one of the cells of a basidium of opposite strains, e.g., U. violacea.
Reproduction: -
It takes place by the production and germination of teliospores into basidiospores the germination of the teliospores. From the individual is uninucleate cells of the promycellium develop the germ tubes, which fuse and bring about dikaryotization.
In U. maydis, at maturity the growth of the dikaryotic secondary mycelium stops, and its most of the binucleate cells starts function as spore initials and are at first enclosed in a gelatinous matrix, but at maturity the matrix disappears. They become globose, enlarged and develop into thick walled unicellular spores called ‘teliospores’. This spore is also called chlamydospore, smut spore, brand spore etc.
The mature teliospore is uninucleate and diploid. Immediately or after a short resting period, each teliospore germinates. At the time of germination the spore wall cracks and a germ tube comes out in the form of promycelium. The septum formation in the promycelium transform it into a septate structure made up of uninucleate cells. The nuclei with in each cell of that promycelium divide into two daughter nuclei, of which one migrates into a bud that develop, at the side of each promycelial cell and the other nucleus remains with in the cell. The so formed uninucleate bud functions as basidiospore. Usually the nucleus remain within the cell of the promycelium which divides again and results into budding off of a second basidiospore. These uninucleate buds or the basidiospore are called conidia. The conidia also behave and germinate like basidiospore.
In U. violacea the teliospore germinates into a 3 - celled promycelium. It gets detached from the teliospore. Even after bein detached the promycelium keeps on producing the basidiospore or sporidia.
Fig. Life cycle of Ustilago.
Q.3. Explain control measures of Smut disease. ( 2011)
Ans. Control Measures of Smut Diseases: -
1. Physical Methods:-
These methods involve exposing the infected seeds to various physical treatment such as -
(i) Solar Energy Treatment:-
In wheat growing regions, where the summer temperature is very high, sun heating technique has been found to be very effective. The infected seeds are given a pre-soaking water treatment for 1 - 5 hours in the hot sun. After soaking the seeds are spread and dried in the sun. During this process, the perminating dormant hyphal are killed and the seeds are dried at the same time.
(ii) Hot Water Treatment:- In this method, the infected seeds are soaked in water at a termperature of 26 - 300C for 4 - 5 hours, which induces the dormant mycelium within the seed to germinate. The seeds are then transferred to hot water at 500C for 10 minutes which kills the internal mycelium.
2. Chemical Method - There are as under -
(i) The seeds are soaked in water containing ceresan or sodium hypochlorite, dried throughly and then stored in air tight containers.
(ii) Loose smut of spring wheat can be effectively controlled by pre-soaking the seeds for six hours in water and then immersing them in 0.2% suspension of Spergon SL for 40-50 hours at 50-720 F.
(iii) The use of systematic fungicides such as carboxin and benomyl at 0-2-0.25% in combination with thiran, maneb or copper quinoleate has been found to be effective.
3. Growing Resistant Varities:-
Sowing grains of varieties of wheat which are immune from or resistant to this disease is the best method of controlling the disease.
4. The infected ears, which emerge out of the boot leaves earlier than the healthy ones, may be uprooted at once and burnt, This practice is called rogueing.
Q.4. Describe the life cycle of Ustilago only by Graphic representation.
Ans.
