Sumbali

INTRODUCTION
Fungi constitute a large group of organisms which are variable in form, behaviour
and life cycle patterns. They are unique organisms as they produce enormous number
of asexual spores which are liberated and dispersed with such a great efficiency that
they can be found in almost every ecological niche. So far, nearly 69,000 fungal
species have been described, whereas, 1.5 million species are expected to exist
worldwide (Hawksworth, 1991).
Fungi are an important group of organisms whose significance to humanity has
been recognized since more than a century, although many of them have been
domesticated unknowingly since thousands of years. Systemic study of these organ¬
isms began in the seventeenth century with the invention of the microscope by van
Leeuwenhoek. The man who is recognized as the founder of mycology (Gr. Mykes
= mushroom + logos = discourse) is Pier Antonio Micheli, the Italian botanist,
who published Nova Plantarum Genera, in 1729, that included his researches on
fungi.
As the fungal kingdom represents a diverse assemblage of organisms with a
great variety of structural types, Ainsworth (1973) listed following main character¬
istics to unite and define fungi:
Nutrition: heterotrophic (photosynthesis lacking) and absorptive.
Thallus: on or in the substratujn and plasmodial, amoeboid or pseudoplasmodial;
or in the substratum and unicellular or filamentous (mycelial) with septa or no
septa; typically nonmotile but motile states may occur (zoospores).
Cell wall: well defined, typically containing chitin or cellulose (Oomycetes) or
both.
Nuclear status: eukaryotic, multinucleate, mycelium homokaryotic or heterokaryo-
tic, haploid, diploid or dikaryotic.
Life cycle: simple to complex.
Sexuality: asexual or sexual (homothallic or heterothallic).
Sporocarps: microscopic or macroscopic.
imi I A A 4>ÿ. WWW A* «nr A wMF

%
&
The Fungi
2
saprophytes, parasites, hyperparasites or symbiont,.
Habitat: ubiquitous as
Distribution: Cosmopolitan.
Presently most of the mycologists use the term fungus (pi fungi) ,0 iJ
eukaryo ic spore-bearing, achlorophyllous organisms that generally reproduce**
Xand asexualty, and whose f,laments branched somatic structures are t>piafc
surrounded by cell wall containing chittn or cellulose or both along with oj
complex organic molecules.
Thallus Organization
Fungi show great diversity in thallus size ranging from single cells to massif
multinucleate growths (Fig. 1A-D). Majority of the fungi, except unicellular one,
composed of unique, threadlike filamentous structures. Each of these filament,
is known as a hypha (pi. hyphae) and they branch profusely forming a networt
called mycelium (pi. mycelia). In the unicellular thalli, bud cells may get produced
in succession which remain attached to one another in an easily dissociated chaii
known as a pseudomycelium (Fig. IB). However, even in some filamentous typa
(e.g., Mucorales), occurrence of a pseudomycelium may take place in the presence
of a high sugar concentration.
In some fungi, thallus may exist either in the filamentous or unicellular fora.
and the phenomenon is known as dimorphism. This change from the filamenw
to unicellular form is generally brought about by change in the environment
conditions. For example, some of the zoopathogenic fungi are unicellular and yeast-
like in the host, but mycelial in culture, whereas, certain phytopathogenic fungi
such as the leaf curl fungus (Taphrina) and the smut fungi have a mycelial thaltas
in the host but a yeast like thallus in culture.
Growth of fungal thallus is centrifugal, with the younger and more active pare
towards the periphery. Eventually, all thalli give rise to reproductive structures, b
the simple, unicellular fungi, entire thallus at maturity becomes converted m
reproductive organ. Such thalli are termed as holocarpic. However, in most of d*
other filamentous fungi, the mature thallus is differentiated into a vegetative p&
which absorbs nutrients, and a separate reproductive part. Such thalli are calld
eucarpic.
The Hypha
The fungal hypha is a microscopic filamem comaining protoplasm a
_a rigid ce I wall which may be uncoloured (hyaline) or dark with yellow or bro*
pigmen, It grows only a, its tip and may be of indeierminaie lengih bul has a
constam diameter, ranging from 2-20 pm depending on the species and alsoon*1
environmental conditions ,o some extern. A major propeny of ihe hyphae of
fung, ,s .he ability to anastomose, that is, neighbouring hyphae in the thallus*stimulated to put out short branches which make contactoMhe tips of two hyl**
ma, eslabhsh comae! w„h each other. A, ,h, poin, of c of lhe h>1*?get dissolved and form a short continuous tube joining ,he two (Fig.
are
nd is bound by
i

Introduclion 3
o:'udc
'CXu.
caliy
othCr
o±)o
G CTo
A B
ssivc
ones,
nents
work
luced
chain
types
•>ence
c D
Fig. 1A-D: Diversity in fungal thallus. A. Unicellular lhallus B. Chains of buds forming
pseudomycelium. C. Portion of branched sepiale hyphae I). Portion of branched cocnocytic
(aseptate) hyphae
form,
nlous
lenial
/east-
ungi,
tallus
Anastomoses helps in creating a strong mycelial network, exchange of nuclei and
possibly also induces efficient cytoplasmic flow and co-ordinated growth of tissues.
Apical region of the growing hyphae is filled with protoplasm and there is
increasing vacuolation of the hyphae behind the apex. The force which thrusts the
growing apex forward is the turgor of the protoplast that is probably
generated by vacuolation. Branching of hyphae takes place at a considerable dis
behind the apex by thinning and softening of (he wall at a poinl whichtance
balloons out as a result of turgor of the protoplast and grows as a new apex that
resembles the main axis (Fig. 3A-C). Branch hyphae have the same general growth
characteristics as the parent hyphae and can in turn produce branches of the
parts
2S. In
into
the
i part
.-ailed
second and subsequent orders.

Xnd by
irown
fairly
HI the
ngher
is are
yphae
JC)-
cBA
Fig. 2 A-C: Anastomosis of hyphae

law# mm
The un
4
■
or coe
I simple
when i
I etes a
intervi
.
cross-
perfor
hypha
.
'
l
G
prima
adven
in the
anoth
appea
myce
contii
omyc
surro
5B).
Basic
septa
indiv
myce
nucle
of h}
the r
as d
netic
uw
CBA
Fig. 3A-C: Growth and branching of a hyphal tip.
u» )>%

EA DCB
Fig. 4A-E: Branching of hyphae. A. Monopodia] B. D.dxaomous C. Svmpodial. D- SuH*
E- Opposite
Branching of hyphae (Fig. 4A-E) is usually monopodial thai is. ihe
branches Tn dichot' k*“ " alon? most acme
EXSZTJXZS™“»'
*■
paired or opposite, or may arise in whorls of ih
8
* bUl SOmel,n,eS the> .
In the -lower’' filamentous ” T" “ '""Sgrowing hyphae are long, muhinucleate and ***** dnd 0om>cctesl'8 '"nucleate and continuous cells known a> coenoc?*
Fig
_

■
Introduction 5
coenocytic (Fig ID) that is. non-septate aseptatc However, even in tkete
simple filamentous forms, septa are formed at the base of reproductive organs or
Nvhcn the hyphae age. In the "higher” filamentous fungi (Ascomycetes. BawdKxnvc-
and Deuteromycetes). protoplasm in the hyphae is interrupted at irregular
intervals b partitions or crosswalls that divide each hypha into cells (Fig, IC>. The
cross-walls are called septa (sing septum. Nevertheless.even these cross walls are
perforated and so the protoplasm as a whole is continuous throughout the funzai
hyphae.
etes
Generally, two types of septa are recognized: primary and adventitious The
primary septa arc formed during nuclear divison between daughter nuclei, whereas.
adventitious septa are formed independent of nuclear divison, as a result of changes
in the concentration of the protoplasm as it moves from one part of the hyphae to
another (Talbot, 1971). An important aspect of cross walls or septa is that ail types
appear to be formed by centripetal growth from the hyphal wall inward. In Asco-
mycetes, the septum has a small, simple pore in its center that allows cytoplasmic
continuity, from cell to cell and organelles migrate through it (Fig. 5Aj. Basidi-
omycetes also have perforated septa, but the opening has a barrel-shaped inflation
surrounded typically by a hemispherical perforated membrane on each side (Fig.
5B). This is called as dolipore septum (Moore and McAlear. 1962). Virtually all
Basidiomycetes have dolipore septa, except for the rusts and smuts. In all the
septate forms, hyphal segments may contain one, two or many nuclei When the
individual cells of septate hyphae contain nuclei that are genetically indezKacai, the
mycelium is said to be homokarvotic. But where a cell or mycelium contains
nuclei of different genotype, possibly derived as a result of mutation or anastomos e
of hyphae, it is said to be heterokary otic. In certain Basidiomycetes. each cell of
the mycelia may contain two generically different haploid nuclei, a coodnsoc called
as dikaryotic. In contrast, mycelia with segments containing single, haploid, ge¬
netically identical nuclei are called as monokary otic.
B
A
overarched with a perforated
A. I'erforaled iepluni B L>- :< r- --Fig. 5A-B: Primary »epla.
A

funs, al certain stages of their life history, the hyphae m
all„f aggregation varying front loosely to compactly woven „SSU5i‘
r*g.Xed fungal tissues ate termed plectenchynra. There are three
of plectenchyma:
Prosenchyma. It is a loosely woven tissue in which the component hyphji
n,ore or less parallel to one another and their elongated cells are easilyÿ
guishable from each other (Fig. 6A).
B Pseudoparenchvma. It consists of closely packed, more or less lsodiametrisj'
oval, thin walled cells resembling the parenchyma of vascular plants (Fig,®
Pseudosclerenchyma. It consists of closely packed, thick walled and dark cei
(Fig. 6C) .
Plectenchyma forms various types of somatic and lepioductive structures.Soir
familiar examples are:
1. Stroma (pi. stromata). A stroma is a compact hyphal aggregation, much like:
mattress or a cushion, on or in which fructifications are formed (Fig. 7A-B
Stromata formation mostly occurs in Ascomycetes, Basidiomycetes ane Fig. i
Deuteromycetes. Examples are the various types of ascocarps, basidiocarp
pycnidia, acervuli, sporodochia, coremia or synnemata.
2. Sclerotium (pi. sclerotia). A sclerotium is a hard resting body formed by
aggregation of somatic hyphae. They are round or elongated or flattened
masses being more or less characteristic for a particular species, in size, shape
and colour (Fig. 8). Small sclerotia (microsclerotia) of Macrophomina phased
may be less than 100 gm in diameter , whereas, majority of sclerotia of other
species do not exceed a diameter of 2 cm. However, some species of polypot®
{Polyporus mylittae) produce sclerotia which weigh several kilograms and may
: ■
*
The f ungi
6
Hyphal Aggregations
types
A.
C
I
I Fig. :
B. C
3.
I
ft4
A
CB
Fig. 6A-C: Types of plectenchyma..Frosenchyma- » IVutluparench) ma ('.

I
Introduction 7
nf
*11
,0a
o 0
ie o
!F
° o °
O 0 o
O 0 ° 0
3r
Is
ie
; a A B!)•
id Fig. 7A-B: Stromatic fungal tissue bearing fructification. A. Acervulus. B. Pycnidium (After
Talbot 1971).IS,
§7c> <7
id
0X A&
a>/i K£TO
Ber
li$es
cay
* Fig. 8: A cross section of sclerotium of Sclerotium rolfsii showing. A. Medulla of intertwined hyphae.
B. Cortex of cells with uniform diameter. C. Rind of empty thick walled cells. (After Deacon 1980).
1 be 25 cm or more in diameter. Sclerotia serve the function of storage and survival
by helping the fungus to tide over periods of drought, cold and moderate heat.
They also serve as propagules from which new mycelia can grow.
3. Mycelial strands. These are aggregates of parallel, relatively undifferentiated
hyphae found commonly in Basidiomycetes and in some Ascomycetes and
Deuteromycetes. A mycelial strand is formed around one or more leader hy¬
phae which grow out from the margin of the thallus, become surrounded by
their own interweaving and anastomosing branches to form a cord, not more
than 1-2 mm thick and a few centimeters long (Fig. 9A). Mycelial strands are
13-

Sf': ,
SSi
I’he Fungi
8
cells and t
(Fig. 9B). i
»i ellea, a s
ground fro
been founc
over 4,000
Mycorrhi;
hyphae. T1
a thick, cc
to the Ag<
and inwari
network’ i
as a systei
performar
mycorrhiz
5.
The Hyphal V
Cell wall of a
may serve a i
1. It determ
2. It acts as
3. It proteci
organism
4. It is pern
5. It acts as
6. It may h
The wall
components.
glucosamine)
wall. Chitin
growing hypl
points and in
group of fun;
cellulose is tl
of Oomycete
Ledieu et al.
01 hyphae, A. Mvccii-ii , , Amorph
■
cdrawn from Webster IQSO, c™"?' Rhiz°morph. C. Myconhiza lA- (polymers ol
Uiaw" bom Harley 1965), cose) which
, upon this. T
U)
afford ;i means by
"
11
composed o1
base to a new substratu1”' lcna|s are a
aggregations of hyphae «
U)|° of large-, thin walled, elot#11'
tl
B
A
cIan. 4M-C: Modifications
capable of translocating ,Ihc lungu.s ciin extend IVo,'.....« Sieved
lM‘«bl.shed food1 Hhizoniorphs. These
well developed apical
hiShly diffe
meristem, a
are
lL‘ntiated ■ith •’
central

Introduction 9
cdls and a rind of smaller, thick walled cells which are darkly pigmented
ik ). 1 best root— like hyphal aggregations are well produced by Armitlaria
nu’ltea, a serious parasite of trees and shrubs This fungus may spread under¬
ground from one root system to another by means of the rhizomorphs. It has
cen *' utR* li:a< ihizomorphs measure upto 4 mm in diamter and may contain
OVCt 4,000 hyphae aggregated together.
5. Mycorrhizas It is a symbiotic association between roots of trees and fungal
hyphae. The root tips of many coniferous and deciduous trees are covered with
a thick, continuous sheet made up of several layers of fungal cells belonging
to the Agaricales. The mycelium extends outwards into the layer of the soil,
and inwards, between the cortical cells of the root, to form the so-called ‘Hartig
network (Fig. 9C) This external layer of fungal tissue replaces the root hairs
system for absorption of minerals from the soil and there is evidence that
performance and nutrient status of mycorrhizal tree is superior than that of
mycorrhizal trees.
as a
non-
The Hyphal Wall
Cell wall of absorptive and vegetative hyphae are thin, less than 0.2 gm thick and
may serve a number of important roles.
1. It determines the characteristic shape.
2. It acts as an interface between the protoplast and the environment.
3. It protects the cell from osmotic lysis and from the metabolites of other
organisms.
4, It is permeable to nutrients, gases and even enzymes.
5. It acts as a binding site for some enzymes.
6. It may have antigenic properties.
The walls of all fungi contain a mixture of fibrillar and amorphous or matrix
components. The fibrillar components include chitin (a polymer of N-acetyl-
glucosamine) and cellulose (a polymer of D-glucose) which give rigidity to the
wail. Chitin is the most usual component of fungal cell walls and its synthesis in
growing hyphae is highly polarised. It occurs at the extreme hyphal apex, at branch
points and in the developing septa. Cellulose is predominantly present in only
group of fungi, the Oomycetes. This is in contrast to the plant cell walls, in which
cellulose is the main component and chitin is absent. Another characteristic feature
of Oomycete cell walls is the presence of the amino acid hydroxyproline (Novaes-
Ledieu et al., 1967)
Amorphous or matrix components of the hyphal wall include proteins,
(polymers of mannose) and (31,3; pJ-6 and a1,3 linked glucans (polymers of glu¬
cose) which are usually embedded within the fibrillar net work or superimposed
upon this The wall of yeast cells have a distinctive chemical property ot be.ng
composed of a mannan-glucan complex (Phaff, 1963). A few additional wall ma¬
terials are also found in the old parts of hyphae and in many spores. The most
one
mannans
nd
ch
a
ed

I he I-'uni
10
notuhlc of Ihcsc ccrnf
deposited as a ■<■** coaling ,„.he
p*......-.......—rs&«"::::::d
Ivtic cnrvmts of other organism* n» np»w “ÿ
' rc,e ty%
...........face of the ".ill and probably help lo prevc„, des,cca„„„.
composinon of fungal cell wall appears lo be correlated with laxonomic
(Table 1).
Composition In Fungi (After Bartnlcki-Garcia, 19«»)
Tabic 1. Cell Wall
Taxonomic group
Cell wall category
Fig.
Acrasiomycetes
Oomycetes
Hyphochytridiomycetes
Zygomycetes
Chytridiomycetes
Ascomycetes
Basidiomycetes
Deuteromycetes
Saccharomycetaceae
Cryptococcaceae
Sporobolomycetaceae
Rhodotorulaceae
Trichomycetes
blacI Cellulose-glycogen
II Ccllulosc-glucan
III Cellulosc-chilin
l Chitin-chilosan
V Chitin-glucan
pla:
in
def
exti
lessVI Mannan-glucan
‘me
Mannan-chitinVII pla:
vvhi
a v
VIII Polygalactosamine-galactan
Wf
l lira-structure of Fungal Cell Ion
Fungal cells are eukaryotic with a rigid cell wall (the structure of cell wall has already
been described). 1 he cell wall is intimately bound to the cell membrane, also knot'11
.1' plasma membrane or plasmalemma that encloses the whole cytoplast. Although
plasmalemma is usually adpressed to the cell wall, it may become undulatinl
or invaginated during certain developmental stages of some fungi under certair
conditions.
a tiipartite structure composed of two electron dense
legions made up ot phospholipid molecules into bilayers and separated by a trans
parent reg.on (Fig. 10) Proteins and sterols (ergosterol and zymosterol) also for*
a large par. ol the cell membrane. The proteins function in membrane transpod
>o, esses, whereas, the role ot sterols is still uncertain The sterol molecules*
1
'lSBphosPhohZrPTheed W'thin
th! ph°SpholiPid bilayers in the ratio of 1:5 or
function during normal vegetal!ve°am T “Sential for membrane structureÿ
membranes when they are available to (he ’cell‘ ***** inCOrp°ra,ed
ahsyPnuderuesSeÿtleShthat?f eukaryotic cells
ribosomes, vacuoles, vesicles, lysosome’s ' °Ch°ndna> microbodies, golgi h°l
(Fig 11A-L). 1, is unique in the 0- ,
endoplasÿic reticulum and microtubÿ
occurrence of specialized organelles such *
sph
len
the
bra
pla
Plasma membrane is
Fig
A.
mer

Introduction >1
m* 5C
lit 10: li.'ÿammatic representation of plasma membrane structure Phospholipids are shown as
black or white dots (hydrophilic regions) with 'tails’ (hydrophobic regions), sterols as stippled
molecule*, proteins as white amorphous molecules (Redrawn from Deacon 1 980).
, asma1emmasomes and lomasomes. They are not present in all fungi and may
in certain other kinds of cells also. Heath and Greenwood (1970) have
defined a plasmalemmasome as ‘the various membrane configurations which
external to the plasmajemma, often in a pocket projecting into the cytoplasm, and
less embedded in the wall material’, whereas, a lomasome has been defined as
‘membranous vesicular material embedded in the wall external to the line of the
plasmalemma.’ It has been suggested that the plasmalemmasomes are produced
when the balance between wall plasticity and turgor pressure is disturbed in such
a way that more plasmalemma is produced than is needed to line the cell wall
When these plasmalemmasomes get extruded in the developing wall, they become
lomasomes.
In fungal cells, mitochondria are of diverse shapes. They range from small
spherical structures of 1 pm diameter that are capable of elongating to 30 pm in
length or to unequally thickened structures. They are present more abundantly in
the sub-apical region of the vegetative hyphae and are enclosed in a double mem¬
brane with the inner membrane thrown into a series of internally projecting, flat,
plate like folds, known as cristae.
occur
are
l>
.'9
'M
in
>e
y jW ■
_-
73 [®> • <m v
Void
o » ’ „
*r
%°0oQO?°re
° I X
& »
*ÿ
b
l)f
*
*oof ©
aC
LI J KG HD E FB CArte
Fig. Diagrammatic representation of a fungal hypha showing apex »nd
subjc*1 region
A Vesicle U. Ribosome C. Mitochondria 1). hndopUsm.c reiiuilum
K JL-na» Rial pore. I Nucleus with nuclear pore -
I Vacuole (Redrawn from Deacon l
&

p— ya'i
I h« Rung'
'»>ÿ/’ S#MC<MT>P;,f:1**v‘'1 y HI
, I <i|(|V 0' OHM ■
’>< <
( dr'; C
(,olgi bodies
(xcn reported in Oomy ' d-'-,/ ate •/{/.' <
r
wards the hyphal 'F/':/.‘iy or
wfij, , Pythiunt
I ) ') am m diarn'however.
posed of 4 or
secretory VCSK
to form larger vesicles.
I ttdoplasmii redleuhim forms an extensive ndw'.ik
It is commonly found in young hyphac and originates from the n Rea? -/<f
It may lx: rough with ribosomes on the external surface or wr.-ou’ sy//ÿ
Ribosomes occur both in the cytoplasm and mitochondria
proteinaceous bodies with a high RNA content and are cor.oern‘-/J
synthesis Some ribosomes may occur free in the cytoplasm and otr.ers are
.ued with the endoplasmic reticulum. Ribosomes aggregate t.o form pohriboyÿ.
S flattened cisteina<-
les which migiate to1
or polysomes.
Cytoplasmic microtubules
cept the extreme hyphal tip. Most of the microtubules are quite long and e sao.
to the long axis of the hyphac. These may be associated v/ith cytoplasm/. " v t,
ment and the maintenance of the cell shape.
Fungal cells possess a number of vac uoles which provide the * mger needed V
cell growth and maintenance of the cell shape Resides vacuoles store rtstnt
materials such as volutin as in the yeasts. Vacuoles also appear to acd.'r .la
pigments, amino acids and hydrolases. The chief storage products of fatis srt
glycogen and lipid which are present as granules and are more apparent » tie
mature cells or reproductive structures.
present everywhere in v.e ceil tytopiaerr.are
f
,r>
a
Nuclei of fungi are very small in size, usually 2 3 prn in d
sionally upto 30 pm in diameter as in Baudioholus ranarum. Rach nucleus
nuclear envelope, a nucleolus and chromatin strands that become organized * :r.
chromosomes during division. The nuclear envelope comprises of two typ.sa. -membranes and the outermost layer has often been shown to be directly cos s>v-t
with the endoplasmic reticulum. In multinucfeate hyphac, the various nude, ssi; te
interconnected by the endoplasmic reticulum. There
of
-F
pores or ano*ÿ
scattered on the surface of the nuclear envelope and sometimes they may be &&
confined to a specific region as in the zoospores of BlaUocladielUi 'ÿ rie '
—'
pores are circular as in yeasts or hexagonal as in Thrauslotheca clavaia ss
octagonal as in Boletus rubinellus and they allow ari exchange of materia-
'
place between the nucleus and the cytoplasm.
are numerous
di
Nuclear Division
Ni, , •In most of the fungi, mitosis is typically intranuclear (closed) that. . ' ;
envelope does not break during prophase as in most other plants and aruma
’ - Ainstead remains intact and constricts in a dumb-bell shape that finally separate httwo daughter nuclei (Fig. I2A-0). J his process has been termed as karvrK'ÿÿ orby Moore (1064). 1 he nucleolus is usually retained during mitosis arid c>-. _divided between the daughter nuclei. In
pears temporarily during mitosis. A
found attached to centriolts
fungi, however, the nudespindle which
>11»
is usually intranuclear, has ■-' y
u dense structures called spindle
(jr
--mall electro

Introduction 13
k’e,
m-
'ÿ"Rto
/ Nce i '
i
i
N /
/
N
1 /m, //
/
i / Iie, i
/i /
ti
*s. /
/
re
! JL
/
‘in
i'#'/:i- ij i
es i
/
/
x~
lei A B C■e-
Fig. 12A-C: Diagrammatic representation of fungal mitosis. A. Metaphase. B. Telophase
C. Interphase. (Redrawn from Moore Landecker 1972).
’or
ve bodies (SPBs) or nucleus associated organelles (NAO). Fungal centrioles are typi¬
cally in pairs and are similar to those of other eukaryotes. Each centriole is a short
cylinder composed of nine triplet sets of microtubules arranged in a ring. However,
in the higher fungi, centrioles are absent and instead a spindle pole body is
ciated with the nuclear envelope. This structure lacks the microtubular components
of a centriole but divides during nuclear division into daughter SPBs which migrate
to the opposite poles of the nucleus just like that of centrioles. Nuclear divisions
involving centrioles are said to be centric and the ones which lack them are called
as noncentric divisions. Fungal chromosomes are small and often appear as patches
of chromatin. During metaphase, the chromosomes are distributed randomly on the
spindle and do not form an equatorial plate.
Meiotic divisions of fungi are also intranuclear but otherwise they are similar
to that of higher plants and animals. As in mitosis, the chromosomes are usually
irregularly distributed on the spindle at metaphase, but rarely they may be aligned
on an equatorial plate.
In most of the fungi, nuclei are haploid throughout the life cycle and the
diploid stage is represented only by the zygote nucleus. However, prolonged dip¬
loid phase similar to that occurring in higher plants and animals, is shown by some
fungi e.g., Allomyces, members of Oomycetes and the yeasts.
ite
je
he asso-
:a-
a
ito
nit
us
be
ili
en
:ar
en
ke
Nutritional Requirements
:ar
>ut A universal characteristic of fungi is that they lack plastids and are completely
heterotrophic. They must obtain nutrients from the environment, from living, dying
or dead organisms. On this basis, fungi are of the following main types:
ito
sis
be
(1) Biotrophs. These obtain nutrients slowly from living host tissues only, often
the host cell
without killing them. Biotrophs secrete chemicals that cause
en
)le

The Fungi
14
acids and as these
membrane to become permeable to sugars or ammo
leak from the host cell, the fungus absorbs them. In biolrophic attack of p|a_.
fungal cells remain confined to intercellular spaces and obtain nourishm*.
through haustoria (sing, haustorium). Haustoria are outgrowths of the soma?
hyphac which penetrate the plant host cells through a minute pore and com,
in close contact with the plant cell plasma membrane, which probably mau
it easier to absorb nutrients by increasing the absorptive area of the parasjÿ
fungus. Haustoria may be variously shaped— knob like, elongated or branchy
like a miniature root system (Fig. 13A-C).
nutrient.
Fig. 14/
the hyph
1(4) Ml
org
my
vas
A B C As
Fig. 13A-C: Types of haustoria. A. Knob like. B. Elongated. C. Branched. (From Alexopoloiu Laborat
their nu
Mo, Fe,
Some fungi even parasitize the mycelia of other fungi without causing damageÿ
to the host, as they cannot grow on dead organic substrata. Such parasitic fungi
especja|are termed as biotrophic mycoparasites. For example, Piptocephalis vir£W“Hmoiety(Zygomycete) is known to parasitize the hyphae of Mucor, another Zygomyceteithjazo|e
(Fig. 14A).
and Mims 1979).
icontainii
h st cells source, t(2) Necrotrophs. These attack living hosts so virulently that they kill the ho
Most ofearly in the course of parasitism and therefore, feed on essentially dead
amountNecrotrophs may also secrete toxins that kill host cells by damaging 4_7t wh<plasma membranes, causing nutrients to leak out rapidly and be readily aable to the fungus. Like the necrotrophs of higher plants, there are necrotrop
Reprodimycoparasites also which parasitize other fungi and kill them. For examp
Trichoderma viride, a common fungus with a world wide distribution in s0
is able to coil around the hyphae of many other fungi, like Rhizoctonia 50and kill them (Fig. 14B)
Reprodui
[of the sp
reprodui
trjcek peated si
(3) Saprotrophs. These attack dead organic matter by secreting digestive/ex cxact e0(
lular enzymes which are released through their walls. These enzymes ac
organs. *
side the fungal body on the surrounding substrate polymers, converting
generally
into monomers (monosaccharides, amino acids and fatty acids) that are rea
sexual cyabsorbed by saprotrophs.
2
I

15
Amu
'ent
4'
■
J
iiQC ]
--.at
A
4 -ÿA— B Mycoparasiles. A. Triehaderma vi.nesn ussiiituuniu T'ramcit m.tei. imim/
* I "nme rf Rhizoctonia solam. 3. -m.f-sjjmh rrnaii rinmnnu mvjnnassie
cr Hfaesr T,srrvT
—-m 3
m r'TlLi;
°iUV
- V ~~ T»lTi reme -J:£. -sr-er “iTin partnership? »'nr. orrer
- ~rir' ~s arc is reremc iun~:ii:TnL ne relarortsmr L.cnzr arc
os r*o roTx: isjccacunsi jf fungi with algae arc -rots- re
_
• iscuier rune resreci <s-
As fungi are
luraratory studies race enro- rrui rung rtssr cniur
rrer rutritiona. raft2ra*ans via rru -ce ~
C . H. N ? £. 5 Vg Zr.. Mr Cu
c they always -sours rrsfrrrreo Tree IT irrasr to fete.
ssKsrrui stsmsm? ir mss:olcui
■ Fe. Ca. Sc
'
rrc 3l Fiar rungs ITS roc : _• -rcresunrc > inias Pu:
11 fcs -e'rrr-1 :r r_ srse cr :o:nr_c ire s. . . .. irrurs- ossc >. —; :_rr..rs
c s
__' ne r--rrr.iO.ns
nrse
iirup
■ijnii <
, cere
ssgeorL neerr ire memoe ir rre rise
— rier- cur i mseced. re fungas reeg ic e r see :ns ir cr— rc-nsr..
■
I — .; — ■■? feme fungi e-er -squrs -ceoci: cr.r; arcs. rose. nr ......I -.-rmmrmr iminn acids. rise cue .r r -aae. Wraftt Ac aeafltt a suitable food
I scums. ~
c-r- i s- moors iconum Tmceririrs. irorsnuc mfi jH Sar proper growth.
if re fungai ipeo.es ITS iusesporus T. restscuonr urc nos -squire some
ir. JO :c carer to grow Tie re£ teenre ~i .urea fungi r;vr • ones berwser
i—
~
vCtersus. optimurr. emreriturs s reevssr I*C and 30~C
sues-
their
IVOJF
phtf
nple-
soih»
olai*
-
irmat nd - - - ? c ...Repraducouii :s
ipcoes. Most of the -arc sorrou-s n : LC
■
_U. ce .-c ■
_j Astro*
M more importicc Kt me ruotuunoo of range srscacs
reutec se-veot times during me .re c-c.e arc Tsults r rr.cL*. n xinsr.c?
•. r.- - .1 SV
U> > C
-ueel-
t
out-
thÿrn
;udily
ropies of the rurent. fe ices not mve- ■
s ce ouoo . n.c e
uivolves the i« A two srmBMC’i: n.c <s anrcrpos.
.-ally, cutes piece .a. • ;rce in a ...... . . r . .
el cycle and instejc practice paneiititr - *
prov ae> a ?• ■. -a
. cac
.

■
The Fungi
16
of genetic variation. Sexual and parasexual cycles arc not mutually exclUsiv
that exhibit sexuality may also accumulate additional and significant variationtlÿ
parasexual reproduction.
A. Asexual Reproduction
ln the majority of fungi, asexual reproduction takes place when a single p,
forms progeny without a nuclear contribution from the second parent. A#,
methods of reproduction commonly found in fung, are as follows:
Fragmentation of the mycelium. Small fragments of mycelium detachedaccifc
from a living thallus are usually able to grow into new individuals if the nr
conditions of growth are provided. This happens frequently in nature and a
method employed extensively by mycologists for growing fungal cultures in d
laboratory. In some fungi, fragmentation of parent hyphae into thallospores (asd
spores) is a normal means of propagation. There are two types of thallospores
arthrospores and chlamydospores. When the distal end of the hyphae breaks
by close septation into component cells that behave as spores (Fig. 15A), sit;
spores are known as arthrospores. They are always formed in a basipetal
(proceeding from apex to the base of the hyphae). In many groups of fungi,
intercalary or terminal segments of the hyphae become packed with food resen
and develop thick wall (Fig. 15B). These thick walled spores are called]
chlamydospores. They form important organs of asexual survival and are releas
after the intervening hyphae is disintegrated.
Fission of unicellular thaili. In this process, the nucleus of a somatic cell diviff
by mitosis and the cell contents divide transversely by a septum into two daugfc
cells of similar size, shape and contents (Fig. 15C). This method is typical of sortypes of yeasts as Schizosaccharomyces.
Budding of somatic cells. It is the production of small bud (outgrowth) fro®parent cell or spore. Each bud grows in size, constricts and finally separates to fo*|a new mdmdual (Fig. 15D). Budding is very common in yeasts Sometimes d>»
°Fig.?B) rCmai" a“aChed f°r
“ Whi'e
‘° f0Tm a P*udom!X<li’
d“fÿrÿ°reS-™S iS ,he mOS‘ co"™°" metbod of asexual
<2-i5° in diamrÿwalled, colourless (hyaline) or variously ““I'''” n°"
type of asexual spores, whereas others mav
SOme fU"gi
A*'"spores serve the triple functions of
y P oduce as many as four types- AP
Propagation, perennation and dispersal-According to their methods of f nUtypes— sporangiospores and conidinc0™3110"’ asexual spores are of two H
formed by the cleavage of cellular •
°F trUe conidia- SporangiospoÿJgium (pi. sporangia) into
numerous °f 3 sac'like structure called sp°
sporangium is borne on specialÿ mUte' typica,1y uninucleate fragments-* {
°r
UnsPecialized hyphal structure
0
0
0
0
0
8
0
Ssuccess
SOT
i
A
«;
*
9
c
Fig. 15A-D: Asexual

Introduction J7
o
0
0
0
B o
8 G
0
0 6
ii
«i
.!
BA
r
0'
9
a •
v_j
I
C D
•in. I5A-I): Ascxu.il reproduction. A. Fragmentation of hypha lo from arthrospores It. Chlamydo&porcs
('. Fission l>. Iludding

The FungiJ8
n
R
a
A
|Fig. 17A-D: Various
B. HyplB
3. Biflagellate zc
the Plasmodic
4. Biflagellate zc
tinsel type, at
zoospore with
A
Fig. 16A-B: Sporangiospores in fungi A. Zoospores. B. Aplanospores.
sporangiophore. On the other hand, conidia (sing, conidium) are produced in v Conl ,osPor*‘ways at the tips or sides of simple or differentiated hyphae called as conidiopyifferentSporangiospores may be motile or non-motile. Motile sporangiosporesare 1
c|eav;
as zoospores and the non-motile ones are called aplanospores (Fig 16A-
°Prtjcu|ar produ
aplanospores develop a rigid spore-wall before their release from the
sP°rÿJ1” p
jn size shap
and are characteristic of Zygomycetes. In majority of aquatic fungi, the CCH Q ,se a simple
contents of the sporangium develop into numerous zoospores. Each zoosporebe equipped with one or two flagella (sing, flagellum). There are atleast |W°JL SeXual Reprodi
of flagella in fungi— the whiplash and the tinsel. The whiplash flagella"1
(
long basal portion and a short and flexible upper portion. The tinsel flagcllt*|lr,imoifeathery structure consisting of a long rachis with lateral hair-like Pr09eCtiO,*S i invob
mastigonemes or flimmers present along its entire length Zoospores are o1„ametangia) follow
kinds (Fig. 17A-D).
* 1. Zoospores with single
Chytridiomycetes.
2. Zoospores with single
Hyphochytridiomycetes.
are remark;
hife cycle of a spec
regulating mechani:
sexual cycles are d
Posterior whiplash flagellum are characteristic j
flagellum are characteristic j
anterior tinsel

Introduction 19
v
0
B C
D
A
Fig. 17A— D: Various kinds of zoospores found in different groups of fungi. A. Chytridioraycetes.
B. Hyphochytridiomycetes. C. Plasmodiophoromycetes. D. Oomycetes.
3. Biflagellate zoospores with two anterior whiplash flagella are characteristic of
the Plasmodiophoromycetes.
4. Biflagellate zoospores with one flagellum of the whiplash type and one of the
tinsel type, attached laterally are characteristic of Oomycetes. This type of
zoospore with two types of flagella is termed heterokont.
Conidiospores, commonly called as conidia, are asexual spores formed in many
different groups of fungi by varied mechanisms. Conidium has been defined as a
non-motile, asexual propagule, usually caducous, not developing by
toplasmic cleavage or free cell formation (Kendrick, 1971). Deuteromycetes,
■HID particular produce an astounding variety of hyaline or coloured conidia which
iÿBvary in size, shape and septation. Conidia arise from a conidiophore that may
ijÿS'omprise a simple cell or a system of conidiogenic cells (Fig. 18A-F).
u
B. Sexual Reproductioni
$
I-ungi are remarkable for their diversity of sexual process. Basically, sexual
reproduction involves a cycle of (1) plasmogamy (accomplished by gametes or
Lametangia) followed by (2) karyogamy, and (3) meiosis at specific points in the
life cycle of a species. These three events are accomplished through a variety of
regulating mechanisms and range of morphological developments. Three kinds of
Isexual cycles are distinguished in fungi:
y|
(i
i*

k s' «ÿ PVB
I hr lung'
20
.....*M th« I...................... , ’
It called uhip......ontk haploid 1 1
the fungi belonging to Mticoralci and Asc
, iinploblonllc-dlplohl life tyde. M (her.- is only one free livhwdj, ., ',7 yclo m a lungus.....called «» huplobx.ni.c dtplotd (I m m,
cycles of .his lype an- li.und in many Oomycetea and in the ye«,
cerevisiae.
I
myers
0
mL)i
□
V
A
B
C P
;
3
Fig. 19A-U
B. Hiplobit*
I
In ma:
modif
mono-
genmi
capabi
trast.
heterc
ent SIT
lype <
J
ED
F
Mg. I8A-F: C’omdiophorcs and conidia
Curvularla. 1».
i F- Alitrnana K. Fusanum

Introduction 21
urinal
lnctina
wiul
'rmlnctina
thallu, tbnllu,
(ÿ>
reduction
dr, ision
reduction
di> ision
gamete*
Y spores or
gametes (n)
fusitÿÿfusion
Zygote.
A B
asexual
reproduction
asexual
.reproduction
thallus
(2n)
Dikarvotic
thallus
(n+n) >*Dikarvotic
basidioca
Zygote (2n)Hxphal fusion
(Somatogamy)
tDikarvotic
basid'iMonokaryonc Monokaryotic
pr. h> phae pr. h phac
uni
reduction
. division
V- y
—thallus
.1karyogamy
fusion
+-Germination
¥- + reduction
di> isionBasidioÿorcsmatureÿ’"'*’"
basidium (n)
(n)
1)
c
Fig. 19A-D: Life cycles of sexually reprodueing fungi. A. 1luplobiontic haploid life cycle
B. Haplobioniic diploid life cycle. C. Modified I laplobiontic diploid life cycle L). Diplobionlic
life cycle.
In many of the higher Basidiomycetes, haplobiontic diploid life cycle is slightly
modified as two functionally different mycelial states can be distinguished, the
- and dikaryon (Fig. 19C). Monokaryon is the primary mycelium formed onmono
germination of a haploid sexual spore and contains a single nuclear type. It is
capable of indefinite vegetative growth and is usually sexually sterile. In
trast, a mycelium containing nuclei of different genotypes is termed a
heterokaryon. It is the result of anastomosis of homokaryotic hyphae of differ
The dikaryon, also called a secondary mycelium, is a specialized
of heterokaryon in which haploid nuclei of two compatible mating
eon-
ent strains.
typeii*

The Funpt
types, mrnrnm,IvMe conjugatclx .unt iMU
‘ , r "cl1 It
otaww! that dikanvn ix the predominant life-style of Has.dmmycet* J
where It is capable of indefinite prap>g«l<on "a,u";- and « ,h«
pre-rÿ
sexual reproduction. The two nuclei in each cell of the dikaryon
discrete during viatic cell divisions. Eventually, the two nude, fuse m
xiuctixe cells, the basidia. and produce diploid nuclei w hich undergo me*
cdiatelv. and prxxiucc sexual spores tbasidiospores). Generally
each basidium. and each basidiospore shares o*
meiosis
Dioecin
female
Nrxuall
produce
On the
of the folio’
repo
almost imm
basidiospores develop on
the tom haploid nuclei produced through 1. Homot
type ol
the con
isolatio
predom
Basidio
homoth
evolvec
• Diplobiontic life cycle. The term diplobiontic means two general;--
he ctorc. in this type of life cycle there is an alternation between a haploid
. :p , d generation (Fig 19D Such type of life cycles are comparatively rare
but have been obserxed in certain members ot the Blastocladiales efungi
. ., . In t '"lyccJ. the alternation of generation is isomorphic, that is.tj
haploid gametophytic generation is morphologically similar to the dtp!.,
-.pv'rophy tic generation. 2. Hetero
duction
develop
heterot
of fun
Saprole
used thi
reactioi
of hete
I he sex organs in fungi are known as gametangia (sing, gametangium). why
may contain differentiated sex cells called gametes or may contain only one
mere gamete nuclei. Morphologically indistinguishable gametangia and gamer:
..re known a* isogametangia and isogametes, respectively, whereas, f
- ; og eally distmet ones, the terms heterogametangia and heterogame;
•ire used In the latter case, the male gametangium is called as antheridiu.
p! antheridia 1
and the female gametangium is called as oogonium (pi. oogoni
; ■
Oomyeetes and ascogonium (pi. aseogonia) in Ascomycetes.
(a) Mi
differentiate, approach eaÿhÿrheTanVfuseÿ't °f fi,ngi are induCed'
considerable variation in form irH 4, .
0rm a z-v§ote. are complex mi
number of tung. is controlled bx matin/o'l"'-Regulatl0n of 'hese processes in
! as hormones* or “pheromones’ u
~ sPeatlc diffusible substances refem
a-t on the same individual that pr 1
are 'he chemical compounds wh:.
■ ndividuals Generally, fungal sex h mrim
' Cm' Pheromones act on differ
consiitutively and others follow
PrtX*uced in very small quantiW outbreeding
1 he simplest hormonal system known 'h UU-°n COrnplementary hormone determined
ualcr mou*d. whose female gametes n 'V 0I_ Allo>»yces (Chytridiomycetes' formation.
cametes Hormonal regulation o
S,renin’ a potent attraetant for
* examples ol
Uv'myeetes Adilya. Pythium. Pin, In] ,'NCVLJal reproduction is also known Sordaria an
iwumyctiV. Ascomycetes (NeurosnUrTV' Zyg°m>eetes ( Blakeslea. .»/«- nism
Ls,,U,*° Cn>Piococcus) ' Saccharo»'yees) and Basidiomyd* types are ir
Un ,he basis of sex. most Qf the .
mycelium t
U"g‘ 'o one of the following tW homothall.c
phi
(b) Ph
ma
ser
Heteroi
some
percent fun;
NJoiUHciuus ilurmaphroditk ( , bi *
Podospora
tx.m male and tenule organs Uut m '' " ‘hese fungi- each thall* exhlblt bipo
> or may not be compatible.
* sategories:
like Unedina
(Fig. 20V b

* MJ
initotUu Mitft 7
1 lout |f, ||„%e
li nialr
Imil!)
*mm f**' 'mly m*u *tt>!i 'Mil ftffyMf*£'lynu
S< imdtfTi
pfndui <‘/1 ih
n filUlxt |f, lb,**
It*1' tfiofjfftoli
I fungi unity film Hotml gift# tut** 4t«
' lni 0,1 / "•'hUnguMtMhl* «» male ,rt Umnk
M* P
,
< hi HK of . i|mMV-»tfity fungi ,,f the *t„v# MM /
lx*j,,„g p, ,rfK.>1 ih« follow "”r*
"» ‘"mpwtnct to elaborate actual
teolation
over the
*»( h individual hat
MU Complete ,hr „MJKi cycf€ In
3 by HUtltr%lr* <<Xy, lUmnhiilhnm n
ornmort It, the, Atcomycetc* awl rare m the
"wjonfy of ike tungi arc bornothalfic
,ri'trArMU ,,,r l>'"i»five condition (ton, which
< k'linol ImlllDrn
predominant in the lower fungi,
Itatidiomyceia*, A*
wet
a may I,* ikA!
hnUtuAhnllnn,
homothallum
evolved later
Hrfrrolhullh fungi. A accond type of thUudkm occur*.
.....;......*«** <'f "»'1"*».., ,„4ivMu,|, .hid, may « w<f
." ................■>< *> ,!I.,K /IV,4, '........"< llymcnomyccfea, l/tfilagtnalet,
" ,r lc,m Iwwiflwllrtra’ B. include oil wefc low u, *l„,h „„
.......1Kxml ,u""" ,,c***•«.....w
/n which tcxual repro
: »n all the major group*
f/redtnafet, I.uattomyccfr*
w curt
'
a
.
'nf Morphological In 1« rolhalllw, refer* io »v/o interacting ihalli Wi»h
pbologically dittlmllar tea organ* or gamete*, male awl female
K rw/r
it
0,ÿ I'hytlohiglcal JurtarothallJam refert lo interacting ihalli which differ
rnaliog type or Incompatibility factor, irretpeefive of the pretence or ah
tencc of differentiated tea organ* irr gameiet,
A
M
lletcrothallltm hat a telctiivc advantage irver bomothallitm at it mtreatet
outdeeding and rctullani variability. In hdcrothaUic Atcomycelet, compatibility ,*
fl determined by a pair of allclct *A(A/ which tegregafe at me.ra.it during atcotprÿe
hrmiaor/n. I hr. it tcrmcrl bipolar or unlfac toral hetcrrahallitm ff-ig 2(>> I yp,cal
■ c/.ample* '/I Av.omycclct with bipolar mating arc tpecict Neurotporu, Au obolu*,
ifl Sordarta awl ( hastomlum, In vmie bipolar hefcrothalbc fungi an inlcrctimg mccha
rutin operate* during tpore formation, whereby, two nuclei of oppotne manng
jfl ly|act are incr/rtxaated in each tjiorc Such tpr/ret, on germination, give rite to a
| mycelium that contain* l>olh ’A/ and 'A/ nuclei and comequently behave* at if
hornolhallr I hit cr/wiition knr,v/n ac tccondary hornothallitm it rqx/rierl ,n 10 |
'•gal tpceiet. for t umpli la tbt font pond Nntrotporo /ttnyfwit
1‘odotpnru amtrlnu (lug 21 j Among Batidiomycefet, r»nly 25 percent
c/bibit bijxflar actual incompatibility f Alexop<;ulot and Mimt, 1979) whereat, <ahert
hie IIredinalc-tf and rraftt r/f tlie (/ttilagmalct tfanv Ulrui*>l*r (Ufartoraf) heierraiu.Hi.m
rl ig 20). In tliete fungi, compatibility ft controlled by two pairt of factora, A A '
tjieclet.d

The Fungi
24
A1B2 A2B1 A2B2A,BiA2A,
A1B1+A2B2
A,B2+A2BiA)+A2Dikaryon
AiA2B1B2Diploid A] A2
FiS
Meiosis
to
by
1.
AiB, A,B2 A2Bi A2B:
TETRAPOLAR
Ai A] A2 A2Spore
BIPOLAR
Fig. 20: Diagrammatic representation of segregation of compatibility factors and polarity
and ‘B, B2’ located on different chromosomes. It is the most complicted pattern 0!
sexuality known among fungi.
C. Parasexuality
There are some fungi, especially the Deuteromycetes (Fungi imperfecti) which lad
a true sexual cycle, but derive many of the benefits of sexuality through parasexu
ality. This is a process in which plasmogamy, karyogamy and haploidization take
place, but not at specified points in the thallus or the life cycle. However, the sexuaand parasexual cycles are not mutually exclusive. Some ascomycetousbasidiomycetous species which undergo normal sexual reproduction exhibit pa*
sexuality also. Discovery of parasexuality led biologistsgenetic material from one individual or cell to another is not thereproduction.
The novel process of parasexuality was first discoverd m Aspergillus «1***by Pontecorvo and Roper (1952). In this filamentous fungus, parasexuality co«»wtth the normal sexual cycle. Pontecorvo(1954) applied the term -parasexual cy*
2
anJ
ter*
poly of
to realise that trans
mono
3.

1ntr<iduLii<m 25
I
Q X . 'I A•A
'•y* +
r0
H B
-*<V?
n•i
•
* ■'
H
' ■
■
Seuroapora utrasptrma.r,. i / fHUnpora or enro <AUcr Pmcham and Dcy I97)>
the sequence of heterokaryosis. fusion of genetically dissimilar nuclei, followed
>J r'yy,mt’,|rÿflon and segregation 7 he essential events of parasexual cycle
Heterokaryosis. Inclusion of genetically different nuclei in the same cytoplasm
. an important pre- requisite for recombination and is achieved through heter-
okaryosis. there arc several ways in which a heterokaryotic mycelium
. , formed, fhe most common way is by anastomosis of somatic hyphae of
different genetic constitution. Another method by which a homokaryotic
mycelium changes into a heterokaryon is by mutation in one or more nuclei, as
shown in some Ascornycetes. A third way is by inclusion of genetically dis-
ar nuclei in a >ingle spore following rneiosis as in Podospora anserina and
Neuroxpora tetrenperma.
2 f usion and formation of diploids. When a mycelium has become heterokaryotic,
nuclear fusion takes place between haploid nuclei of different genotypes. Nuclear
f jsion in heterokaryotic vegetative cells was first noted by Roper fl952). The
frequency of spontaneous somatic diploids is usually very low. In A. nidulans
it is about I in 10M0 conidia. Heterozygous diploids are relatively stable
at mitosis and their colonies carry mainly diploid conidia of the parental
type. Conidia of diploid strains are significantly larger than those of
id. The ratio of their diameter is almost 1.3:1.0 and the volume is in the
ratio of 2:1.
Mitotic segregation During multiplication of the diploid nuclei, mitotic
crossing-over takes place which represents an extremely important step in
pure .e/ .al cycle Mitotic crossing-over is a rare event and a very characteristic
feature of this is that chiasmata formation is confined to a single chromosome
pa>r out of the whole complement of chromosomes. These recombinations
give the fungus some of the advantages of sexuality within the parasexual cycle
are:
.

HiPHI
The Fungi
26
estimated that crossing-over occurs once in every 50
It has been
divisions.
4 Haploidization. The diploid nuclei give rise to haploid nuclei by gradual |()s
chromosomes during successive mitotic divisions. Th.sis called haploidiÿ
Meiosis is not involved and instead haploidization is the icsult of aneuplÿ 1,1
’
During mitotic divisions, non-disjunction of the chromatids of one chromoso, rh
pair results in aneuploid nuclei. The aneuploids arc genetically unstable,„
once the loss of chromosomes has started, it continues to lose chromoson*
probably one at a time, until the haploid condition is restored.
Therefore, parasexual cycle closely resembles sexual cycle as both the proc s
esses end up with similar results, that is, give rise to recombinant haploid nuclei Gem.
However, the events of sexual reproduction are extremely uniform, having a fin
-
coordination between recombination, segregation and reduction, whereas, there
such coordination in parasexual cycle. Genetic recombination achieve) thal
through mitotic ‘crossing-over’and ‘haploidization’ is also called as somatii molt
recombination.
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Ot'l
S
Fam
l
no
may
som
orga
sub!
systi
prog
attei
Nomenclature and Classification
Nomenclature of fungi is governed by the International code of botanical nomen
clature, as adopted by each International Botanical Congress. The Congress ap
points the Committee for Fungi (CF) which advices on action to be taken of
proposals concerned with fungi. In determining the correct name for a taxon, fivi
steps are to be followed— effective publication, valid publication, typification, legiti¬
macy and priority. The name of a fungus is a binomial, that is, it is composed o
Asc(
two words. The first is a noun designating the genus in which the organism hi' clas,
been classified and the second is often an adjective, describing the noun, whicl Barr
denotes the species. Binomials are usually derived from Greek or Latin, with ft four
genus name always in capital and that of species not capitalized. Binomials whtf Hyp
written should always be underlined or italicized and followed by full name c c|ass
abbreviated name of the scientist who first described the species (e.g., Penicillin nine
chrysogenum Thom). If a species is transferred from one genus to another, or h* Plus
its rank changed, then the name of the original describer is given in brackets a* Basi
the name of the one making the change is cited otuside the brackets e.g., Fusari*poae (Peck). Wollenw., is based on the earlier Sporotrichum poae Peck. Someth subc
the year in which the organism was described is also written after the author’s nan* fung
The,, author citations help taxonomists in finding the original description of *organ,sm and also aids m avoiding confusion when different authors unknown1'different species.
The application o scientific names to the categories into which fungi n*
be placed and the relative order of these
k
, ,A bV 1
International Code of Botanical NomenctuVS™).“ ®
that
did
use the same binomial to name

IIII!< M lilt Hull
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in y i i |i n
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I Il'IllU >>111 1it*
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I lllll'l IlilVl* ltl'l‘11 *lilSSll|l‘t| ||lllll Him I" lima by various myiuiluiihit, using
l|u"‘ulm' lapiodiniive Mimlmas, ulliiwlimimu Uml mum ,e*«uily iln
.....'ÿ
' ul
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' 1,11 111 1 '
Many dllTi I- in . .ii in ii*. I, , i. ,,, DI , i,, ..........i,
mas Iw tint* to ineomplala dniu mi iln siimiiu , developni«f)J iiml physiology ul
lunt'i. mill lliU nmy prnhtthly lonliuue nil 111111« knowledge ,ilium iln
u'lmiHMns is obtained I m ll> 1, luiiÿl W9|e plm n| undei division IliuJIopliyfu ul Hi.
subkingdom ( rypingnmiie ul ilu Mndmn IMimlm- iwaii l.mnmm. iln Uuiin ul
s ii-nmin biology planed lungi m iln* plum kingdom bul
pi ogic*NM*t 1, 11 became evident ilml I’ungi lira neiilmi plunk uoi uinmnU In
mirmpt in solve 1I11u piiihleni, hnsl IImu lu l, iln* < k imoil Miologisi pmpot ..1 m 1 ;u,u
ilmi u iblul Kingdom, dn I'rollalii, ha iai ogni/ed lo im Iml* smIi oigmusuw /dm li
ilnl mil belong lo #|tliei plum 111 miiiiml I- iiigduin
some in 1 HI lUH"
ii" nm iut>< uiiii sludu I,
1in
I ln* true lungi were divided by Niitvmdo ( I MNHj lulu lum < In . i*liy * umy. , u
Aaconiyteles, Ilnsitlloniyt'eleN mill I>«-nit iomy< < i* > Hus lum ■ 1,1 sysn m ul Imig.d
1 lu-.Mlli'iilion doinillllleil I01 U long Him mill WIIU III •1 pil’d liy < iwynmi* V.ingli.iii ,IIUI
Umnfs ( 103 /), WolI uml Woll ( IW| /), Iiisaey ( IO’)!)) I .mi ‘ipuuuw 1 m ugm/i <1
lour t Im.'.i", wllldn Ilies m|imlli I'hytoiliycclrs Ilie * III ' "** < liyliidUiniy* n .
IlypbmliylrldlomyCMlis, Oumyeeles mill l*hi*iiii«llo|ilM»ininy»eles I uilui ul.
1 l.isM- Zygomycete* uml TileltomycHe* ware alsu given iln 1 mil ul .I* llm
ul lungi v1/ ,< liyliidioiiiyi eieh, llypliowliyiiidiumy » i< •>l IIISSI'Snine
Plemnodiopboromyeaii"., ( Joinyeai* s, Zygomycetes, I 11* liouiyi * i* s, AM nmy ei*
liiwidiomycrles mid I Jeulcromyceles weie lonmd
Alt nopouloh (l%2) plated llie lungi in division Myiolu mid mugni/id 1*0
siihuis 1.inns iln- Mynomycollmi m line slime molds, mid iln lOimyiolbm m i.m
lungi An outIim* ul linn datilMellon IN given on nod png*

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