Deuteromycotina
Q.1. Discuss the general characters and classification of class Deuteromycetes. (2011)
Ans. Subdivision Deuteromycotina include those Fungi which lack sexual reproduction, and in commonly known as Deuteromycetes of Fungi imperfecti.
General Characters of Class Deuteromycetes:-
1. The class Deuteromycetes or Fungi Imperfecti includes those group of fungi which perfectly lack sexual reproductive organs and sexual stages.
2. The members of this class mostly resemble to Ascomycetes and Basidiomycetes in structure and reproduction.
3. The fungi of this class cause many important plant disease which cause sufficient damage to the crops.
4. The vegetative mycelium is endo or ectophytic, inter or intracellular, branched , hyaline or brown, septate and reniculate.
5. The sexual reproduction takes place by means of conidia, chlamydospore.
6. The sexual reproduction is completely absent.
Alternaria
Q.2. Give an account of structure and reproduction in Alternaria.
Related Questions -
Q. Describe life history of any Deuteromycetes ember you have studied.
Q. Write short note on Early blight of Potato.
Q. Describe disease symptoms of Alternaria. (2001, 06)
Q. Give systematic position of Alternaria. ( 2007)
Q. Write the name of the causal organism, symptoms and control measure of early blight of potato. (2007)
Q. Draw neat and labelled diagram of hypahe with conidiophore and conidia of Alternaria. (2008)
Ans. Systematic Position: -
Division - Mycota
Sub-division - Eumycotina
Class - Deuteromycetes
Order - Moniliales
Family - Dematiaceae
Genus - Alternaria
Occurence and Symptoms:-
Alternaria causes a well known disease “Early blight of Potato” which is widely found in India and abroad. It attacks Solanum tuberosum the potato plant. The first symptom of disease appear three or four weeks after the crop is sown. Alternaria causes considerable loss to potato crop.
Fig. Twig of potato plant Infected by Alternaria
The fungus appears in the form of small isolated yellowish brown spots called lessions in the early stage.
The infection spots are rounded angular due to checked growth across the veins. In the begining there are few spots and as the infection becomes severe, it involves large part of leaf surface and petiole also shows the infection spots. The stem or tubers also show infection. The spots grow in size as concentric circular rings giving an effect of “target board”. The mature spots become black or dark brown in colour and the disease progresses upward. Abundance of moisture and high temperature favours the infection whereas a continued drought checks it.
Mycelium:-
It is intercellular as well as intracellular. The mycelium consists of branched, slender, septate light brown hyphae. The hyphae becomes dark at maturity. The cells are multinucleate. The haustoria are absent A.tenuis attacks wheat, A.zinniae attacks compositae and A.brassicae attacks mustard cruciferae.
Reproduction:-
Sexual reproduction is totally absent and the fungus reproduces asexually. The pathogenecity of the fungus is due to the presence of alternaric acid found in the fungus. The asexual reproduction takes place with the help of conidia. The conidia are produced in chains terminally on conidiophores. The conidiophores emerge through stomata. The conidiophores are difficult to distinguish from the somatic or vegetative hyphae. The conidiophores are dark coloured aerial, simple, septate, short or elongated structures.
Fig. V. S. of infected leaf of potato showing conidiphores
The conidia are multicellular and of various shapes. The conidia are mostly elliptical or ovoid. The conidia are dark in color with typically transverse and longitudinal septa. The number of septa varies from 5 to 10. The size of conidia ranges from 30 to 130 in length and 12 to 30 in breadth. In Alternaria tenuis the conidia are produced in chains and they show acrogenous manner (youngest conidium at apex).
Germination of Conidia:-
The conidium germinates rapidly in the moist atmosphere and forms 5-10 germ tubes. The germ tubes infect the host generally through stomata, but rarely penetrate directly through the epidermal wall.
Control of Disease:-
The disease can be controlled by:-
1. Rotation of crops.
2. By periodical spraying of Bordeaux mixture.
3. By checking moisture and dampness in the field.
4. By proper drainage system.
5. By burning the dead parts of plant immediately