1. Heterothallism is the production of two types of fungal structures (thalli or hyphae) designated as + and - strains. These structures undergo nuclear fusion to form zygotes. 2. Blakeslee demonstrated that in heterothallic fungi species, zygospores are only produced when hyphae of opposite strains (+ and -) fuse together. No zygospores are formed when hyphae of the same strain fuse. 3. Fungi produce sex hormones that facilitate the recognition and fusion of opposite strain hyphae, allowing for reproduction. Examples include trisporic acid in Mucor mucedo and alpha factor in yeast.

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2. Heterothallism is production of two types of
thallus/hyphae in fungi, designated as the +
and – strain. These hyphae undergo nuclear
fusion to produce zygote.
Example:Rhizopus
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3. 1.Ehrenbergh in 1829, for the 1st time studeied
zygospores in the order Mucorales.
2. The American Mycologist “ Blakeslee” in 1904
reported that in the several genera of the order
Mucorales the zygospores are not formed at all.
3.He also supported his view with facts and reasons.
4.And also investigated that in same order two types of
species are found which may be named as Homothallic
and Heterothallic species.

4. 5. When the two Hyphae of the same
mycellium proudced by a single spore fuse
with each other and a Zygospore is
developed, the species is said to be
HOMOTHALLIC
EX : Mucor hiemalis
(When male and female organs are present in
the same fungi are termed as
HOMOTHALLIC
EX: Puccina
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5. 1.In heterothallic species the fusion can take
place only among the different strained hyphae.
2. Which develop on different mycelia of
different + and - strains.
3.In these species the zygospores cannot be
produced by the fusion of two hyphae of the
same strain.
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6. 4. In 1904, Blakeslee reported that heterothallic
species ,whenever the mycelia of + and – strains
remain apart from each other the zygospores are not
produce and only the sporingia are formed
5. On the other hand ,when + and – mycelia grow
together , the fusion takes place , and the
zygospores are produced .
6. Morphologicially ( shape / structure ) the + and –
strained mycelia are quite similar in structure but
different in physiological behaviour .
(in other words there are morphologically identical
and physiologically different )
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7. 7. Sometimes it has also been observed that
the growth of +ve mycelium is comparatively
faster
8. And the gametangia ( specialized organ /
cell in which gamates are formed ) of +ve
mycelium are bigger than that of –ve
mycelium .
9. And they can be distinguished as male and
female gametangia .
10. Many mycologist do not support this view
and said that this behaviour is only because
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8. 11. Blakeslee prove that the phenomenon of
hetrothallism on the basis of experiments .
 he inoculated many + and – strained spores on the
agar medium in petri dish .
 And observed that the fusion occurs only at those
points where the hyphae of the different (+ and - )come
in contact.
 The zygospores where only produced at the points of
contact of different strained hyphae .
 Absolutely no zygospores were produced at the
points of contact of same strained hyphae .
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9.  this expt may be clearly understood by the figure given
in text.
 5 spores of different strains are inoculated in a sterilized
petri dish on agar medium at different five points designed
as A B C D and E . KKR1116 9

10.  The zygospores are produced only at those points where
the
mycelia are opposite strained and produced from + and –
spores designed as A C and E are + ve strained .
 The zygospores are produced at the junctures of AB
BC DE and AD were the opposite strained mycelia take
part in fusion.
 The zygospores are not produced at the junctures of AC
and AE because of the mycelia of same strains .
 Blakesleev also investigated if the +ve strained hyphae
of one hetrothallic species fused with the –ve strained
hyphe of another hetrothallic species the imperfect
zygospores are result . KKR1116 10

11.  in such conditions the zygospores do not mature.
 he also inestigated that in the heterothallic species
Mucor mucedo the zygospores produced
germsporangia on germination .
 which contain single strained spores and therefore
the fusion is possible only when the mycelia are
produced from the spores formed in different strained
germsporangia .
 in the heterothallic species of phycomyces nitens the
+ and – strained pores are produced in the same
germsporangium .
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12.  the phenomenon of heterothallism was first reported in
the order Mucorales , but now this has been established in
rusts , smuts , homobasidomicetidae and other fungi .
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13. FUNGAL SEX HORMONE
 Fungal harmones : a substance that is produced in one
portion of an organism and moves by diffusion and
transport to another portion of the same individual or to
the other individuals of the same species where it induces
specific responses is called harmone .
TYPES OF SEX HORMONES IN FUNGI
1. TRISPORIC ACID : Trisporic acid was discovered in
1964,as a metabolite that caused enhance carotene
production in Blakeslee trispora
2. It was later shown to be hormone that brought about
zygophore production in Mucor mucedo .
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14. 2. YEAST ALPHA FACTOR: The alpha factor pheromone
arrests the yeast in G1 phase of their cell cycle.
 Alpha factor pheromone induces the expression of mating
genes ,changes in nuclear architecture, and polarzes
growth towards the mating partner.
3.SIRENIN: it was the first fungal sex hormone to have its
structure determined.
 it is produce by the female gametangia and gametes of
chytridiomycete genus Allomyces and attracts male gametes
of the genus.
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15. 4. ANTHERIDIUM AND OOGONIUM
 The sex organs ,which are morhpologically distinct , consist of
a tubular or lobed male organ.
 the antheridium ,and a spherical female organ ,the oogonium.
The female continuously secretes a substance called Hormone A ,
to which the male reacts by producing branches on which
antheridia are borne.
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16. REFERENCE
 https://www toppr.com
 https://www. Your article library.com
https://en.m.wikipedea.org
https://www.science direct.com
https://online library.wiley.com
Botany for degree students-B.R.Vashishta
A.K.Sinha
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