In vitro cultures by androgenesis and gynogenesis. Haplo-dipoidization techniques and production of haploids and diploids plants.
الزراعات الزجاجية. النشوء الذكري والنشوء الأنثوي

Vocabulaire - مفردات - Vocabulary

In vitro cultures by androgenesis. Haplo-dipoidization techniques and production of haploids and diploids plants.
الزراعات الزجاجية. النشوء الذكري

ANDROGENESIS (Motherless plants).

Androgenesis is the regeneration of whole plants (haploids and then diploids) from the culture of male sex cells (immature pollen grains (= microspores)),
- either by culture of isolated pollen,
- either by culture of whole anthers.

The Objective of androgenesis:

The objective of androgenesis and gynogenesis is to obtain doubled haploid plants, (after spontaneous or artificial doubling by colchicine). Thus pure lines are produced in a few months instead of 8 to 10 years by the classic technique of self-fertilization.
Obtaining inbred lines is an almost always necessary step in plant breeding programs. Indeed, homozygosity confers stability and phenotypic uniformity, and thus makes the agronomic behavior of lines predictable. A high homozygosity is required for the registration of new cultivars, and it allows, at the same time, to reduce the frequency of undesirable alleles during the selection phase.

Advantages of the androgenesis:

- Expression of recessive genes that can be masked in the diploid plant (dominance). - Expression and easy identification of mutants.
- Use of androgenesis in plant selection & genetic improvement programs. Thus, different characters can be researched for improvement. For examples:
--- Fruit shape.
--- Early flowering.
--- Resistance to diseases or abiotic stresses (drought, salinity, cold, etc.).
--- Yield.
--- Richness in secondary metabolism compounds.

Disadvantages of Androgenesis by anther Culture:

- Production of genetically different/heterogeneous plants.
- Production of a heterogeneous population at different levels of ploidization.
- The asynchronous development of pollen will lead to the suppression of younger grains by older grains due to the release of toxic substances.
- Plants from anther culture would not be of purely gametophytic origin.

Advantages of androgenesis by pollen cultures over anther cultures

- The pollen culture is a haploid and unicellular system.
- Pollen grains bearing an androgenic response can be isolated using the density gradient centrifugation method.
- Production of a homogeneous population.
- Production of genetically identical plants.
- Pollen grains can be easily modified by exposing them to mutagens or genetic engineering.
- Pollen culture is 60% more efficient than anther culture in terms of embryo production.

Haploid plants are sterile and stunted: they must undergo diploidization (= doubling of the number of chromosomes). Diploid and completely homozygous plants are obtained.

How to double the chromosomes?

- By colchicine:

At low concentrations colchicine applied (eg on the terminal bud) makes it possible to double the chromosomes in metaphase.

- By culture of the calluses: spontaneous diploidization after a few weeks, eg in tobacco.

Stages of an androgenic culture

Two scenarios:
-- Formation of calluses, then embryos (indirect embryogenesis), e.g. in rice. -- direct formation of embryos (direct embryogenesis): rapid acquisition of bipolarity: ex. in tobacco.
Note: after passing through callus, there is a possibility of the appearance of chromosomal aberrations.
Importance of anther maturation stage.
- Need for a very precise stage of anther development at the time of culturing: e.g. --- uninucleate microspore stage in grasses.
--- stage of pollen mitosis in tobacco.
To find these stages, one must look for a relationship between the stage of microspore maturation and the morphology of the flower.
The best stages are always before the flower buds open. - Ex: petal length in tobacco.
- Position of the ear in the sheath in wheat (size of the ear at 2/3 of the sheath of the leaf ex wheat).
Possibility of verification under the microscope: staining of the cells with carmine.