2. Basidiomycotina
Diagnostic features of Basidiomycotina
1. Basidiomycotina comprise of about 550 genera 15,000 species
2.Many of them are saprophytes while others are parasitic. These includes
mushrooms, toad stools, puff balls, stink horns, shelf fungi, bracket fungi,
rusts, and smuts.
3.They have Septate mycelium ,non motile spores and are characterised by the
production of a club-shaped structure, known as Basidium
4. Basidium is a cell in which karyogamy and meiosis occurs. However, the
basidium produces usually four spores externally known as basidiospores
Vegetative structure: The vegetative body is well developed mycelium which
consists of septate, branched mass of hyphae which grow on or in the
substratum obtaining nourishment from host. Sometimes, a number of
hyphae become interwoven to form thick strands of mycelium which are
called rhizomorphs. In parasitic species the hyphae are either intercellular,
sending haustoria into the cells or intracellular. The colour of the hyphae
varies according to the species through three stages before the completion of
life cycle.
3. Three stages of development of mycelium
The three stages are the primary, the secondary and the tertiary mycelium.
The primary mycelium consists of hyphae with uninucleate cells. It develops from the
germinating basidiospore. When young, the primary mycelium is multinucleate, but later on, due
to the formation of septa, it divides into uninucleate cells. The primary mycelium constitutes the
haplophase and never forms basidia and basidiospores. The primary mycelium may produce
oidia which are uninucleate spores, formed on oidiophores.
The secondary mycelium is composed of binucleate cells and represents dikaryophase in the life
cycle. The binucleate condition is attained from the uninucleate condition, a process known as
dikaryotisation or diploidisation. The binucleate or secondary mycelium is also known as
dikaryon mycelium. The basidiomycetes have a shortlived uninucleate (monokaryotic) stage and
a dominant binucleate stage. The binucleate or dikaryotic condition may arise by one of the
following ways:
1. by the union of two primary (monokaryotic) hyphae of opposite strains.
2.by fusion between the germ tubes of two basidiospores of opposite strains
3.by conjugation between two secondary basidiospores of opposite strains that are
produced by budding of the basidiospores.
4. by the union of basidiospore of one strain with the germ tube of opposite basidiospore.
5. By the union of two infection threads.
6. By the fusion between two basidia formed by germination of small spores of opposite strains.
The tertiary mycelium when the secondary mycelium forms complex tissue to develop fruiting
bodies or basidiocarp it is called as tertiary mycelium
4. Classification of Basidiomycotina
• Ainsworth divided sub- division Basidiomycotina
into three classes-
1. Teliomycetes
2. Hymenomycetes
3. Gastromycetes
Two orders 1.Uredinales -Puccinia
2.Ustilaginales-Ustilago
Order-Agaricales Agaricus
Only those orders and genus are indicated which are in course
9. Class-Gastromycetes
• Basidiocarp is present
• The basidiocarp remain closed until the spores
have been released from the basidia.
• Class gastromycetes have been divided into
following orders- 1 Hymenogastrales
2. Nidulariales(Bird nest fungi)-Genus Cythus
3.Phallales
4.Lycoperdales(puff balls) eg. Lycoperdon
5 Sclerodermatales
10. Dikaryotization/Diplodisation – Primary or monokaryotic mycelium is
converted into secondary or dikaryotic mycelium is called as dikaryotization
or diplodisation. It can brought about by following methods
11.
12.
13. CLAMP CONNECTION
• The secondary dikaryotic mycelium produce structures called as clamp
connections. These are the characteristic features of Eubasidiomycetes
and were first observed by Hoftman. Its development was first studied
by kniep (1915) and Bensaudi (l918). It allows the migration of a nucleus
from one cell to the other. The clamp connections formation takes place
as follows
The two nuclei (+ and -) of the terminal cell of a mature dikaryotic
hyphya divides simultaneously(conjugately) into four nuclei. (+, + and , -
). Simultaneously, a pouch like outgrowth arises from its wall(Fig. A, B).
One of the nuclei of the upper pair passes into the pouch and is cut off
from the main cell by a septum at the base of the pouch. It may now be
called a clamp cell (Fig. C, D). Simultaneously, one of the nuclei of the
lower pair gets separated from its sister nucleus by a transverse wall
(Fig. E). At this stage the terminal cell has two nuclei, the cell below it
(penultimate cell) has one nucleus, while the fourth nucleus lies in the
clamp cell. The clamp cell grows into hook like structure. Its tip bends
over and finally fuses with the lateral wall. The walls at the place of
contact dissolve and the fourth nucleus passes into the primary
penultimate cell (Fig. F). Thus, the clamp cell serves as a by-pass or a
bridge to transfer nucleus one cell to the other and is known a clamp
connection.
•
15. BASIDIUM & BASIDIOSPORES
• Basidium – The basidiospores are formed externally on the
basidium which is also known as mother cell. Two nucleus are
present inside the young basidium which later on fuses . The fusion
nucleus divides to form four nucleus which gets converted to
basidiospores. The basidiospore develops at the end of the stalk
known as sterigma, through which the nucleus passes from the
basidium to enter the developing spore. Two successive divisions in
the basidium constitute meiosis. In the Homobasidiomycetidae the
basidia are without septa, and four spores arise from, or near, the
apex of the basidium. In Heterobasidiomycetidae the basidium
divides into four cells, each of which gives rise to a single
basidiospore. In the Ustilaginales septa may or may not be present in
the basidium. Here more than two divisions follow nuclear fusion,
and more than 4 basidiospores are produced.
In the Ustilaginales and the Uredinales the basidium
develops from a thick-walled chlamydospore (brand spore)
or teleutospore (teliospore). On the gemination of brand
spore or teleutospore the contents extrude out in the form
of a thin-walled promycelium or basidium on which the
basidiospores are produced.
16. A. Young teleutospore B.mature teleutospore
C. germinating teleutospore with young basidium
D. germinating teleutospore with basidium and basidiospores (2+ve and 2 –ve basidiospores)
Puccinia sp. teleutospores
17. Basidiospores. The basidiospores are unicellular, uninucleate, rounded, or
oval and haploid. The basidiospores usually remain assymetrically attached
to their sterigmata. They are colourless or pigmented. The pigments may
be green yellow, orange, pink, brown or black. They are usually smooth and
thick-walled. When a mature spore is about to be liberated, a droplet of
water begins to form at its basal end. The droplet gradually enlarges in size,
and ultimately the basidiospore is shot off the sterigma. The basidiospores
germinate in water by means of germ tubes which later on develop into
uninucleate mycelia.
Teleutospores, Basidium &
Basidiospores of Puccinia
graminis tritici
18. Types of Basidia On the basis of structure and development there are
several types of basidia found in Heterobasidiomycetidae and the
Homobasidiomycetidae . Fig A showing Stichobasidial type with a cluster of
sporidia,Fig B showing Stichobasidial type with separate 4 sporidia,Fig C
showing chaistobasidial type, Fig D showing Tuning fork type , Fig E
showing Holobasidial Type
19. Basidia of Homobasidiomycetidae
• In class Hymenomycetes and
Gastromycetes basidia are of
different shapes. In
Hymenomycetes(E&F) basidia are
slender clavate or broadly clavate
while in gastromycetes basidia are
globular. The diploid nucleus
divides twice forming 4 haploid
nuclei. Four sterigmata arise from
the apex of the basidium and a
uninucleate basidiospore is formed
on each sterigmata
20. Basidia of Heterobasidiomycetidae. In Ustilaginales and Uredinales,
the teliospore is a diploid, thick-walled, probasidium & on germination it
gives rise to the basidium or promycelium. Meiosis takes place and four
haploid nuclei are formed thereafter the basidium becomes transversely
septate and a row of four cells each containing one nucleus is formed. Each
nucleus then migrates into a laterally or terminally formed bud, which
converts into a basidiospore (fig A). In Ustilaginaceae the primary haploid
nuclei within the basidium may continue to divide, and as a result many
basidiospores may be produced.
Fig A
