Apomixis and its Application for crop improvement.

PRESENTED BY: Pawan NagarReg. no.: 04-2690-2015M.Sc.(Fruit Science)

Apomixis refers to the development of seed without sexual fusion (fertilization).

In apomixis embryo develops without fertilization.

Thus apomixis is an asexual means of reproduction.

Apomixis

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.

Apomixis in crops

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.

POWERFUL BREEDING TOOLS

Adventive Embryony:- Embryo develop directly from vegetative

cells of ovule such as nucellus, integuments and chalaza.

No development of embryo sac. This is a type of Sporophytic budding. E.g. Citrus, Mango.

Classification Of Apomixis

Apospory:- Some vegetative cells of the ovule

develop into unreduced emrbyosac without meiosis.

Embryo then develops directly from diploid egg cell without fertilization.

E. g. Malus, Crepis, Poa, etc.

Diplospory:- Embryosac is produced from the

megaspore which may be haploid or more generally diploid.

Diplospory leads to Parthenogenesis or Apogamy.

Parthenogenesis:-

Development of embryo from the egg cell without fertilization.

Two types:- Haploid parthenogenesis Diploid parthenogenesis

Haploid parthenogenesis occurs in Solanum nigrum.

Diploid parthenogenesis occurs in Taraxacum.

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.

For this, anthers or pollen grains are cultured on a suitable tissue culture medium. This technique offers possiblities for crop improvement.

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.

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.

Reproductive Behaviour

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.

Application of Apomixis

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.

DETECTION OF APOMIXIS

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.

Problems in utilization of Apomixis

THAnk YOU.