There is a tremendous variety of morphologically different conidia produced. The study of development of conidia based on its origin is referred to as “Conidial Ontogeny”.

1. Presented by-
Akanksha Shukla
Dept. Of Plant Pathology
Conidial Ontogeny

2. Contents
 Introduction
 Saccardoan spore types
 Conidial Ontogeny
 Types of Conidium development
 Hughes’s Classification
 Conclusion

3. Introduction
Deuteromycetes fungi are the septate, mycelial fungi which reproduce
exclusively by asexual means and are known as imperfect fungi or
anamorphic fungi. They lack sexual stage (telomorph) and are believed to
represent the conidial stage of higher fungi. The asexual reproduction is
through conidia (mitospore). There is a tremendous variety of
morphologically different conidia produced. The first attempt to classify
these conidial fungi was of Saccardo’s. The study of development of
conidia based on its origin is referred to as “Conidial Ontogeny”. The two
principle types of conidum ontogeny are ‘Thallic’ and ‘Blastic’. Hughes
proposed eight different types of conidium development based on its
origin.

4. Saccardoan Spore Types
P.A. Saccardo (1845-1920)
 “Sylloge Fungorum” (1882-1972)
 Developed first system of classifying Hyphomycetes fungi based on
morphology of spores:-
Color
 Hyaline or bright (hyalo-)
 Pigmented (phaeo-)
Shape and Septation
1. Amerosporae:
Conidia non septate, spherical, ovoid to elongated.

5. 2. Didymosporae:
conidia two-celled, ovoid to oblong.
3. Phragmosporae:
conidia 3 or more celled by
transverse septa.
4. Dictyosporae:
conidia divided by both transverse
and longitudinal septa(muriform).

6. 5. Scolecosporae: conidia
slender, filiform, one to several
celled; hyaline or coloured.
6. Helicosporae
(Allantosporae): Conidia
cylindrical, curved (allantoid);
hyaline or coloured.
7. Staurosporae: Conidia stellate
(star-shaped), radiate or trifurate,
one to several celled; hyaline or
coloured.

7. Conidial Ontogeny
 Conidia/Conidiospores -(sing. conidium) Conidia may be defined as
asexual, non-motile spore that belong to the anamorphic stage of a fungus
life cycle.
The word is derived from the Greek konis ‘dust’ + the diminutive
suffix -idium (Sutton, 1986).
 Conidiophore -Specialized hyphae that bears one or more conodiogeneous
cells.
 Conidiogeneous cell - The hyphal cell from which a conidium is formed
directly.
 Conidiogenesis - The process of formation of conidium.
 Conidia may originate from conidiogeneous cells by either of the two
ways:-
1. Thallic
2. Blastic

8. Thallic Conidiogenesis
(Gr- thallos= branch) conidium arises by conversion of a pre-existing
segment of the fungal thallus.
a) Holothallic – All the layers of conidiogeneous cell contribute towards
the formation of conidium wall.
e.g. Microsporium gypseum
b) Thallic-arthric - The conidia are formed by dissolution of septa along a
hypha. e.g Galactomyces candidus (Geotrichum candidum)

9. Blastic Conidiogenesis
The conidium develops by the blowing out of the wall of cell, usually
from the tip of a hypha.
a) Holoblastic- Conidium elongates and swells before being cut off by
septum. Both inner and outer layer of conidiogeneous cells are
involved, e.g. Cladosporium, Sclerotinia fructigena.

10. b. Enteroblastic- Only the inner wall layers of the conidiogenous cell
are involved in conidium formation.
i. Tretic –Conidia develops by protrusion of inner wall through a
channel in the outer wall.
Monotretic Alternaria Polytretic Curvularia

11. ii. Phialide
(Gr. phialis = flask), usually shaped
like a bottle with a narrow neck.
Conidiogeneous cell wall with an
open end through which a
basipetal succession of conidia
(phialospore) develops.
e.g. Penicillium, Aspergillus
iii. Annellide
(Lat. Annulus = little rings)
A conidiogeneous cell that extends
and retracts as it produces conidia
often leaving a succession of scars
or rings.
e.g. Scopulariopsis

12. Development of conidial loci
- Cole (1986)

13. Arrangement of conidia at locus
Seriate
A. Solitary-Conidia
formed singly or
in chains
Conidia produced in
groups at a locus
B. Catenate- true chains
are formed with a
conidial wall layers in
continuity.
C. False chain
D. Spore
heads

14. Conidial succession
 Basipetal
Youngest conidium at the base. e.g.
Penicillium.
 Acropetal
Youngest conidium is at the tip.
e.g. Alternaria, Cladosporium.

15. Dehisence of Conidia
A. Schizolytic dehisence -(Gr. schizo= to split, divide). Shizolytic
dehisence occur when the two wall layers of delimiting septum
seperate e.g. majority of Ascomycetes.
B. Rhexolytic dehisence - (Gr. rhexis = a rupture, breaking) The
entire septum seperates with conidium, often tearing the cell
directly below. e.g. Onygenales

16. Types of Conidial Development
Type I - Blastic-Acropetal or Blastic-Synchronous conidiogenesis
Type II - Blastic-Sympodial conidiogenesis
Type III - Blastic-Annellidic or Blastic-Percurrent conidiogenesis
Type IV - Blastic-Phialidic conidiogenesis
Type V - Blastic-Retrogressive conidiogenesis
Type VI - Basauxic conidiogenesis
Type VII - Thallic-Arthric conidiogenesis
Type VIII - Thallic-Solitary conidiogenesis
-By S.J. Hughes

17. Type I - Blastic-Acropetal or Blastic-Synchronous
Conidiogenesis
Type II - Blastic-Sympodial conidiogenesis
Blastic acropetal -Cladosporium
anamorph of Mycosphaerella tassiana
Blastic synchronous-
Botrytis and Gonatobotryum
Leptographium anamorph of
Ophiostoma
Beauveria

18. Type III - Blastic-annellidic or Blastic-percurrent
conidiogenesis
Type IV : Blastic-phialidic conidiogenesis
Spilocaea anamorph of Venturia inaequalis.
Penicillium, Aspergillus, Fusarium, Trichoderma

19. Type V: Blastic-retrogressive conidiogenesis
Type VI: Basauxic conidiogenesis
e.g. Basipetospora, Trichothecium and Cladobotryum.
e.g. Oidium anamorph of Erysiphe spp.

20. Type VII: Thallic-arthric conidiogenesis
Type VIII: Thallic-solitary conidiogenesis
e.g. Geotrichum anamorphs of Dipodascus spp. (Saccharomycetes), Coremiella
e.g. Microsporum anamorphs of Nannizzia

21. Hughes’s Classification
S.J. Hughes 1953 classified Hyphomycetes based on conidial
ontogeny i.e. their origin :-
1. Blastospore: Conidia borne as
buds or blown out tips.e.g.
Cladosporium,Torula.
2. Gangliospore: Conidia developed
from the swollen tip of the
conidiophore. e.g. Scopulariopsis,
Amblyosporium.
3. Porospore: Single or whorl of thick
walled conidia formed through one
or more small pores in sporophore
wall .e.g. Alternaria, Curvularia,
Helminthosporium

22. 4. Phialospore: Conidia borne on short
unicellular, oval or sub cylindeical or
flask shaped phialides with a distinct
basal swelling and a narrow distal
neck.e.g. Aspergillus, Penicillium.
5. Arthrospore: Conidia formed by
breaking of hypha into cells. e.g.
Geotrichum.
6. Aleuriospores: Conidia borne on blown
out ends of hyphal tip and cut off by
septum. e.g. Trichothecium.
7. Redulospore: Conidia borne on little
pegs/ sterigmata on surface of
conidiphore. e.g. Botrytis, Ramularia.

23. CONCLUSION
The conidial fungi demonstrate a broad range of
morphogentic complexity in which the hypha is a
fundamental element from which reproductive
structures (conidia) are derived. In both thallic
and blastic development the hyphal tip is the site
of pivotal events which leads directly or indirectly
to conidium differentiation.

24. References
Alexopolous C. J., Mims C. W., & Blackwell M.
Introductory Mycology, John Wiley & Sons, Inc.
pp 219-233
Aneja K.R. and R.S. Mehrotra 1990. An
Introduction to Mycology, New Age
International Publisher. pp 417-423
Cole G. T. 1986. Models of Cell Differentiation in
Conidial Fungi, Microbiological Reviews, 50(2),
pp 95-132
Cole G. T., and Kendrick, W. 1981. Biology of
Conidial Fungi Vol 2., Academic Press New
York. pp 272-322

25. Thank you