This PPT intends to explore the basic characters, ecology and importance of the group of Ascomycetes fungi.

1. MYCOLOGY
Ascomycotina: General Characteristics(Asexual & Sexual
Fruiting Bodies) Ecology & Life Cycle
By
N. Sannigrahi, Associate Professor,
Dep't. Of Botany, Nistarini College,
D.B. Road,Purulia
West Bengal, India

2. INTRODUCTION
 The Ascomycota are morphologically diverse. The group
includes organisms from unicellular yeasts to complex cup
fungi. There are 2000 identified genera and 68,000 species of
Ascomycota. The unifying characteristic among these diverse
groups is the presence of a reproductive structure known as the
ascus known as sac though in some cases it has a reduced role
in the life cycle. Due to the presence of ascus, it has been
termed as ‘sac’ fungi and the ascus bears non-motile
ascospores in the sexual stage of the reproduction. As a group,
they are economically important. Many are tree diseases, such
as Dutch elm disease and apple blights. The yeasts are used to
produce alcoholic beverages and breads. The mold Penicillium
is used to produce the antibiotic penicillin.The group deserves
importance having industrial value like the production of
breads, alcohols, cheese and other industrial products
including steroids and antibiotics.

3. SOME MEMBERS OF ASDCOMYCETES

4. GENERAL CHARACTERS
 (i) Most of the members are terrestrial, although a large
number lives in fresh and marine waters. The majority of
ascomycetes are saprophytic, some are parasites of insects and
other animals, and some are responsible for causing
destructive plant diseases. Some ascomycetes
characteristically grow on dung and are popularly called
coprophilous fungi (Peziza).
 (ii) The members vary in their form and structure. Yeasts and
other a few members (e.g. Taphrina) are unicellular, but almost
all other members of this group have a well-developed,
profusely branched, and septate mycelium with uni or
multinucleate cells and perforated septa.
 (iii) In unicellular forms, the cell wall is composed of glucans
and mannans, whereas in septate forms it consists of chitin
and glucans.

5. GENERAL CHARACTERS
 (iv) Asexual reproduction takes place by various types of non-
motile spores, such as oidia, chlamydospores, and conidia. In
unicellular forms, fission, fragmentation, and budding are the
most common methods of propagation.
 (v) They are homothallic or heterothallic. In some heterothallic
species, though male (antheridium) and female (ascogonium)
sex organs develop on the thallus of the same strain, they are
self-incompatible. In these species, male gamete of one mating
type fertilizes ascogonium of other mating type. This process
is known as physiological heterothallism.
 (vi) Sexual reproduction takes place by gametangial copulation
(e.g., yeast), gametangial contact (e.g., Aspergillus,
Penicillium, Erysiphe), somatogamy (e.g., Peziza, Morchella)
or spermatization (e.g., Polystigma).

6. ASEXUAL REPRODUCTION
 Asexual reproduction takes place by several methods like fission,
fragmentation, budding, chlamydospores and conidia. Fission 7
budding mostly found in yeasts while conidia and chlamydospores
are found in almost all the members of this group.
 Conidia are borne on the conidiophores and conidiophores are two
types- micronematous (not differentiated from vegetative
mycelium) or macronematous (can be differentiated) produced
either basipetal or acropetal succession.
 The conidiophores aggregate to form conidioma and different
types of conidioma are found to form specialized structure like-
 1. Acervulus-
 2. Pycnidium,
 3.Sporodochium
 4. Synnemata

7. REPRODUCTION
 (vii) The sexual spore is haploid called ascospore, which
is formed endogenously by free cell formation after
karyogamy and meiosis within a sac-like or cylindrical
structure referred to as an ascus. If the sexual spore of a
fungus is an ascospore, the fungus is an Ascomycete
regardless of any other character. This one character
distinguishes Ascomycetes from all other fungi.
 (viii) They show the phenomenon of heterokaryosis, i.e.,
the nuclei of two different genotypes are present in the
same mycelium.
 (ix) The fruiting bodies are known as ascomata (sing.
ascoma; earlier called ascocarp). The ascomata are of four
types cleistothecium (cleistothecial ascoma), perithecium
(perithecial ascoma), apothecium (apothecial ascoma),
and ascostroma (stromatic stroma) or pseudothecium.

8. SEXUAL REPRODUCTION
 Sexual reproduction ranges from isogamy to oogamy but in higher
Ascomycetes, there is a gradual reduction of sex organs but the
basic features of sexual reproduction-Plasmogamy, Karyogamy &
Meiosis takes place in orderly manner. It may be –
 1. Isogamy- In homothallic species, sexual branches arise in pair
and each branch receives a nucleus from the parent cell and form
gametangia. The two tips of the gametangia fuse to form
plasmogamy by gametangial copulation to form 2N zygote,
undergoes meiosis to form ascospores .Homothallic species are
self compatible.
 2. Heterogamy-By gametangial contact or gametangial copulation
or somatogamy or spermatization, the sex organs, antheridium &
ascogonium fuse together to establish dikaryon followed by
diploid cell to form secondary mycelium. This produces ascus
either by direct or indirect method.

9. DIRECT DEVELOPMENT OF ASCUS
 Karyogamy immediately after plasmogamy and diploid state is
established,
 The zygote enlarges directly to form ascus and the 2n cell directly
behaves as ascus mother cells,
 The 2n nucleus undergoes meiosis followed by mitosis to form 8
nuclei,
 Cytoplasm gathers around each nucleus and the protoplast forms a
wall around it to form ascospores,
 The formation of ascospores is thus by a cell formation not by
cleavage,
 The asci remain naked without being enclosed by any sheath or
sterile mycelia to form any type of fruit bodies like ascocarp.

10. FRUIT BODIES-ASCOCARPS

11. IMPORTANCE TO STUDY
 (i) Some Ascomycetes cause destructive plant diseases such as
Dutch elm disease (Ceratocystis ulmi), ergot of rye (Claviceps
purpurea), apple scab (Venturia inaequalis), powdery mildews
of various crop plants (Erysiphe, Phyllactinia, Uncinula, etc.),
and many others.
 (ii) The most interesting Ascomycetes are the yeasts which are
variously significant because they are involved in the
production of many products of bakery and brewing industry.
To appreciate their significance in human’s welfare, one must
only smell and taste newly baked bread or an alcoholic drink.
 (iii) Claviceps purpurea causes ergot disease. Ergot contains a
variety of alkaloids including LSD (lysergic acid
diethylamide), the well-known hallucinogenic drug of the day.

12. IMPORTANCE TO STUDY
 (iv) Penicillium spp. are involved in production of penicillin,
the wonder drug.
 (v) Many ascomycetous fungi are used in production of
cheese. The Japanese and Chinese often use the members of
‘Aspergillus flavusoryzae group’ to produce foods and
important industrial alcohol.
 (vi) Neurospora genetics laid down by Dodge provides a new
approach of haploid genetics and biochemical genetics. This
became possible only because the fungus Neurospora opened
up a new way in the study of heredity.
 (Vii) Extends a number of ecological significance as a part of
the sustainable development and the soil fertility.
 (Viii) It also play a very important role for academics and
research purpose.

13. ASCUS FORMATION WITH ASDCOSPORES

14. INDIRECT DEVELOPMENT OF ASCUS
 The following steps are followed in indirect development:
 1. The Male and female nuclei do not unite immediately; dikaryons
established,
 2. An asogenous hyphae arise from the ascogonium
 3. The dikaryons in the ascogonium undergoes several conjugate
division and the resultant dikaryons migrate into the ascogenous hyphae
 4.The young asogenous hyphae become dikaryon having antheridial
and ascogonial in origin,
 5. One of the binucleate cells subterminally becomes curved to form
crozier. Now each of the nucleus of the crozier undergoes conjugate
division and arrange themselves in such a manner that –uninucleate
terminal cell, binucleate subterminbal and uninucleate antepenultimate
cell.
 6. The binucleate penultimate or sub terminal cell now behaves as ascus
mother cell.

15. INDIRECT METHOD
 7.Now the karyogamy occurs in the ascus mother cell nucleus by
synkaryon
 8. The synkaryon divides by meiosis followed by one mitotic
division to form 8 haploid nuclei.
 9. The rest of the steps are followed as per direct development
method where each nucleus now have surrounded by cytoplasm
and form a wall to form meiospores.
 10. In the meantime, the vegetative hyphae in between asci
elongate and form paraphyses.
 11. The asocogenous hyphae get surrounded by common sterile
hyphae and the entire structure transformed into the ascocarp.
 12. The four types of ascocarps are formed- Apothecium,
Perithecium, Cleistothecium and Hysterothecium.

16. T.S OF ASCOCARP

17. LIFE CYCLE OF ASCOMYCETES

18. ECOLOGY & OCCURENCE
 World wide in distribution
 Occur almost in all ecosystems –terrestrial, fresh water and
marine including Antarctica,
 White truffles found to grow in Italy & East Europe
 Mostly saprophytes while others grow as necrotrophs and
biotrophs in plants and animals causing diseases,
 Some members grow as endophytes but harmless
 40% grow as symbiotic mode as in Lichen,
 Also enjoy mycorrhizal relationship,
 Decompose lignin, cellulose called lignophilous groups
 They also grow as symbionts with arthopods,
 Due to diverse color, they are called blue, green molds.

19. ACKNOWLEDGEMENT:
 Google for images
 Different open source materials by visiting different websites,
 Mycology & Phytopathology by Mishra & Dash
 A text book of Mycology-Vasistha & Sinha
 A text book of Botany ( Vol I) by Hait, Bhattacharya & Ghosh
 College Botany-Chakraborty, Ganguli & Kar