Q.6. Define fungi and give the characteristic features of fungi.
Ans. The fungi, broadly speaking, are achlorophyllous thallophytes or chlorophyll-less non - vascular plants that live parasitically or saprophytically and reproduce by characteristic spores. There are about 80000 known species of fungi in the world. The branch of botany that deals with the fungi is called mycology and the scientist who study this branch of botany known as mycologist. The study of disease caused by fungi in plants known as Plant Pathology and the scientist who study about these diseases known as Plant Pathologist.
There are some characteristic features of fungi:-
(1) Fungi lack chlorophyll.
(2) They are heterotrophic in nutrition.
(3) They obtain their nutrition as saprophytes or parasites.
(4) The plant body of fungi is mycelium which have net work of filaments the hyphae.
(5) The cell wall or hyphae wall is of fungal cellulose or chitin.
(6) Reserve food is usually glycogen and not starch.
(7) Fungi reproduces asexually by accessory spore and meiospore formation.
(8) Sexual reroduction show gradual and progressive simplification from lower to higher groups.
Q.7. Write in detail the classification of fungi given by Ainsworth.(2007)
Ans. During the early periods fungi were kept under division thallophyta of the Sub kingdom Cryptogams of the kingdom plantae Saccardo 1866 divided true fungi into 4 classes Phycomycetes, Ascomycetes. Basidiomycetes and the ‘form class’. Deuteromycetes on the basis of presence or absence of septa and characteristic, sexually produced spores such as oospore, zygospore, ascospores and basidiospores.
The Phycomycetes are called algal fungi and are known as lower forms of fungi Ascomycetes, Basidiomycetes and Deuteromycetes are called higher fungi. The four classes of classification of fungi dominated mycology for a long time but it was felt that the sub - class oomycetes was an assemblage or unrelated forms. In 1943 F. K. Sparrow laid emphasis on flagellation of the zoospores and divided aquatic phycomycetes into two series, uniflagellatae and biflagellatae. Later in 1958 he recognised four ‘galaxies’ in aquatic phycomycetes and named them as four classes equal in status to ascomycetes and basidiomycetes Sparrow considered flagellation a good taxonomic and phylogenetic character. The four classes are Chytridiomycetes, Hyphochy tridiomycetes, Oomycetes and Plasmodiophoromycetes, and sub - class Zygomycetes of the class Phycomycetes was also upgraded to the rank of a class.
A group of Phycomycetes which are internal parasites of arthopods was also elevated to the rank of a class. The classes are:
1. Chytridiomycetes 2. Hypochytridiomycetes
3. Plasodiophoromycetes 4. Oomycetes
5. Zygomycetes 6. Trichomycetes
7. Ascomycetes 8. Basidiomycetes and
9. Deuteromycetes (fungi imperfactii).
Alexopoulos (1962) named the division as Mycota and spearated Myxomycetes and true fungi under two sub - division the myxomycotina and Eumycotina.
Another important change in the classification of fungi came in the year 1966 when G. C. Ainsworth proposed a classification in the Dictionary of Fungi, (1971) and also followed in his book “The Fungi, An Advanced Treatise” Vol. IV 1973 written by Ainsworth, Sussman and Sparrow. In this classification fungi are treated as a separate kingdom.
The outline of classification as suggested by Ainsworth is as follows
Class Plasmodiophoromycetes because of certain common characters, is included in both Myxomycotina and Eumycotina.
Q.8. Describe the criteria for the classification of fungi. (2009)
Ans. The classification of fungi is still in a state of flux. A stable and ideal system of classification is yet to be proposed. With the advancement of knowledge newer systems are proposed while the older ones are discarded. The classification of fungi is mostly based on the following criteria-
1. Nature of somatic phase whether unicellular or a mycelium, if latter septate or aseptate.
2. Kinds of asexual spores (mitospores) - sporangiospores or conidia if former motile or non-motile, number and arrangement of flagella in the motile spores.
3. Kinds of sporangia.
4. Nature of the life cycle - whether asexual, haplontic, diplontic, haplodiplontic or haploid dikaryotic.
5. Presence or absence of the perfect or sexual stage.
1. Nature of Somatic Phase -
(a) The vegetative phase of a fungus is a thallus. It may be unicellular or filamentous. Unicellular thallus of the lower fungi such as Chytrids. The thallus is more or less spherical, single called structure. At the time of reproduction it becomes a reproductive unit. The latter produces the asexual or sexual cells.
(b) The vast majority of the fungi have a filamentous thallus. It originates through the germination of a spore. The thallus is technically called hypha. The hypha is a structural unit of the mycelium. Mycelium may be septate or aseptate. In the algal fungi the mycelium in the vegetative phase usually lacks internal partitions of any kind. The hyphae are thus multinucleate and aseptate, called coenocytic mycelium. The classes of fungi such as Assomycetes and Basidiomycetes develop internal cross walls in mycelium, called the septa. In a septate rnycelium the septa between the cells are tranverse.
2. Kinds of asexual Spores- In fungi following types of asexual spores are found —
(i) Motile spores - They are generally found in lower fungi and produced within big sporangia. Motile spores are flagellated. The flagella are of two types tinsel or whiplash. Some spores consist of eithert insel or whiplash type and some consist of both types.
Example — Pythium, Phytophthora etc.
(ii) Non — motile spores: - They are also formed within sporangia and are small in size. They are unicellular and germinate to form new mycelium, e.g., Mucor etc.
(iii) Conidia: - Their shape is round like spores but they are not formed within sporangia. They are developed at the tip of specialized branches called conidiophores. They are borne exogenously and usually arranged in chains, e.g., Albugo, Aspergillus etc.
(iv) Chlamydospores: - They are thick — walled, brown or black colour spores, They are formed from each cell of mycelium e.g., smuts etc.
(v) Oidiospores - They are generally produced when fungus is grown on culture medium.”
3. Kinds of Sporangia: - The sporangia found in fungi are of following types-
(i) Filamentous — e.g., Pythium monospermum
(ii) Spherical or Globose — e.g., Pythium debaryanum
(iii) Elliptical and lemon shaped — Phytophthora
(iv) Ovid — e.g., Plasmopora
(v) Round — e.g., Rhizôpus
(vi) Button shaped collumate — e.g., Pilopolus.
4. Nature of the Life Cycle: - Nature of life cycle is one of the most important criteria for the classification of fungi. Following types of life cycle patterns are found in fungi-
1. Haplontic Life Cycle: - In this type of life cycle pattern, the gametophytic phase is very long, e.g., Phytophthora.
2. Diplontic Life Cycle: - In this type of life cycle pattern the dipoloid phase is dominant i.e. diploid phase of life cycle is very long, e.g., Physarurn.
3.Haplodiplontic Life Cycle: - This type of life cycle consists of two phases which are known as haplophase and dikaryotic phase, e.g., Ustilago.
4. Asexual Life Cycle: - The fungi which represent this type of life cycle do not show .seximl or perfect stage. They ,reproduce asxually by the method of sporulation. In this type of life cycle haploid or gamete phytic phase is completely absent, e.g., Alternartia.