apomixis, gametophytic, adventitious,aposposry, diplospory,apogamy, parthenogenesis, types, androgenesis, semigamy

1. Sub.:- Fundamentals of Plant Breeding
Course No. :- APB- 5211
Credit hours:- 3(2+1)
Lec. Topic :- Apomixis and its Application for crop
improvement.Presented by:-
Lt. Roshan Parihar, Asstt. Professor
Deptt. of Genetics& Plant Breeding
Indira Gandhi Krishi Vishwavidyalaya
Raipur, C.G.
BTC College of Agriculture & Research Station
,Sarkanda, Bilaspur,(CG)-495001

2. • ‘Apo’ means away from and ‘mixis’ means
mingling or mixing.
• Thus “Apomixis" refers to the
development of seed without sexual
fusion (fertilization).
• In apomixis embryo(भ्रूण) develops without
fertilization (निषेचि).
• Thus apomixis is an asexual means of
reproduction.
(असंगजनन)

3. Identification in over 300 species belonging
to 30 families.
Most frequently found in families like
Compositae, Rosaceae, Graminae,
Asteraceae.
Thus it is not rare but relatively uncommon.
Amphimixis:- Normal union of gamates in
sexual reproduction is called as amphimixis.
•Apomictic plants represents the character of
mother only since male gametes are unused.

4.  Apomixis is potentially a powerful
breeding tool to fix heterosis.
 But it is nuisance when breeder desires to
obtain sexual progeny because
recombination of crossing is impossible.

5. Types of Apomixis
1.Gametophytic apomixis
2.Adventitious apomixis
Embryosacs are formed from unreduced initial cells.
Egg cell develops parthenogenetically.
Sporophyte-gametophyte-sporophyte cycle but
embryo forms from unreduced gametophyte.
Mainly concerned with polyploids.
1.Gametophytic apomixis
Its types:-
1.Apospory-
2.Diplospory-

6. Apospory:-
•Without the use of sporophytic MMC cells.
•Some vegetative cells viz. Nucellus, integuments
cells of the ovule develop into unreduced emrbyosac
without meiosis.
•Embryo then develops directly from diploid egg cell
without fertilization.
•In most cases polar nuclei is fertilized by Sperm
(pseudogamy) are necessary for endospermdev. And
seed viability.
•E. g. Grass family, pennisetum, Poa, cenchrus etc.

7. Diplospory:-
• With the use of sporophytic MMC cells by
circumvention of meiosis.
• Meiotic divisions are omitted or modified.
• Embryosac is produced from the megaspore which
may be haploid or more generally diploid.
• Diplospory leads to Parthenogenesis or Apogamy.
• Endosperm dev. Autonomously from unreduced
polar nuclei.
• Pollination is not necessary as req. in apospory.

8. In mitotic diplospory MMC will not enter meiosis
and give rise to unreduced gametogenesis
(alike sexual ovule but with diploid egg cell)
Mitotic diplospory
Meiotic diplospory
In meiotic diplospory MMC will enter meiosis I stage
but FDR (First division restitution ) taken place .
Nucleus doesnot undergo separation of homologous
chro. at anaphase I.
The mitotic division give rise to two unreduced
spores identical to each other.
In both cases 8 nuclei unreduced embryosac is
formed which form embryo thru. Parthenogenesis.

9.  Adventive Embryony:-
• Embryo develop directly from vegetative cells of
ovule such as nucellus(बीजाांडकायज), integuments
(आवरण) and chalaza(निभाग).
• Usually occurs around normal embryosac where
nucellual cells become embryogenic without
forming embryo sac and results in
polyembryony.
• This is a type of Sporophytic budding.
•  E.g. Citrus, Mango.
अपस्थाननक भ्रूणता
2.Adventitious apomixis

10. Parthenogenesis:-
 Development of embryo from the egg cell or
female gametophyte in the absence of
pollination or any other stimulus from male.
 Two types:-A. Haploid parthenogenesis
B. Diploid parthenogenesis
 Haploid parthenogenesis occurs in Solanum
nigrum.
 Diploid parthenogenesis occurs in
Taraxacum.

11. Types of Parthenogenesis:-
Gonial Parthenogenesis:- When embryo develops
from egg cell.
Somatic Parthenogenesis:- When embryo develops
from somatic cells other then embryosac. Viz.
Androgenesis :- It is a rare form of haploidy where
embryo develops directly from the sperm cells
after it enters embryo sac.
In many species, e.g., Nicotiana, Datura, Rice
etc., pollen grains may be induced invitro to
produce haploid embryos or plantlet; this is
called Androgenesis.

12. For this, anthers or pollen grains are cultured on a
suitable tissue culture medium. This technique
offers possiblities for crop improvement.
Automixis :- embryosac remain undivied in second
meiotic phase or fusoin of two haploid nuclei After
normal megasporogenesis. Results in diploid Cells with
homozygous constitution.
Semigamy :- Spl type of parthenogenesis where
gametogenesis is normal but fertilization doesnot takes
place .
Male nucleus penetrates egg cell but not get fused with egg
cell.both divide independently.
Chimeric expression means some cell have male characters
and some have female character. Ex. cotton

13.  Apogamy :-
The origin of embryo from either
synergids or antipodal cells of the
embryosac is called apogamy.
Two types:- Haploid apogamy
Diploid apogamy
Diploid apogamy has been reported in
Allium, Iris and many other species.

15.  Obligate apomictic:- Reproduction in
plant by only Apomixis.
 Facultative apomictic:- Sexual
reproduction also occurs in addition to
Apomixis.
 Many crop species show apomixis, but it
is generally facultative.

16.  Apomixis is used to achieve following
objectives:-
 Fixation of Heterosis.
 Fixation of Heterozygous state.
 Rapid Production of Homozygous Lines.
 Production of phenotypically stable
population called Vybrids.

17. •In case of obligate apomixis, progeny
from cross resemble female parent.
•In case of facultative apomixis, percent of
progeny identical to female parent gives the
degree of apomixis.
•In selfed generation, presence of plants
showing no inbreeding depreesion is
indicative of apomixis.
•Embryological studies of young ovules
confirm apomixis.

18. A very complicated phenomenon. Its
utilization necessitates reorientation of
breeding program and seed certification.
Estimation of apomixis in case of facultative
is tedious and time consuming.
Genetic base of apomixis is not clear in most
cases.
Limitations of Apomixis