Backcross in plant breeding and genetics

Backcross in plant breeding and genetics

Backcross in plant breeding and genetics is defined as a cross between offspring of two parent (HybridF1) and of its parent plant is called as backcross.

In this method the offspring between two parent and progenies in the next generation and the

Repeated a cross to the f1 generation of a parent.

Why backcross is used…?

The Backcross is used to transfer a character.

Some varieties which are grown are deficient in character when it grown in recurrent parent. So that recurrent parent is crossing with those in which character is not deficient in donor or non recurrent parent.

Objective of backcross method:

The main objective of this method to improve some imperfection of high yielding variety to those area which is used for that having desirable character.

Purpose of backcross breeding:

It is breeding method which is basically used for recurrent genotype without the separation of that allele which is successfully used for unique expression of character which is basically contributed from non recurrent parent or donor.

It is considered as inbreeding form which is used for improving feature of recurrent parent with the help of successful backcross.

The donor parent is a selection which is only used for the contribution of unique trait.

It is depending upon breeder to vary the backcross 2 to 5 times to recover the gene from recurrent parent.

\Procedure of this cross is turn to be more easily if character added in this method is simply dominant, inherited and recognized easily in the offspring of plant.

What is Recurrent Parent….?

It is defined as transfer of gene in a more or few number to the non recurrent parent or donor parent is called recurrent parent.

Non Recurrent Parent or Donor Parent:

It is defined as transfer of gene in a more or few numbers to the recurrent parent is called donor parent.

Backcross requirement:

  1. It is attain a suitable form of recurrent parent which is short of one or more character.
  2. To attain a intense form of character in recurrent parent which is deficient in that parent.
  3. High heritability character which is composed of one or more than one gene.
  4. For attaining full recovered form of genotype of recurrent parent then sufficient backcross should be made.

Application of Backcross method:

  1. Backcross is a method which is basically used for transferring of disease resistance of variety from one to another. This method is also used for transferring other character.
  2. Simple inherited character intrvarietal transfer.

E.g Colour of seed coat

Disease resistance.

  1. Quantitative character transfer.

E.g. Height of plant

Size of seed

Shape of seed.

  1. Transfer of interspecfic simply inherited character.
  2. Disease resistance is transfer from related species to those which is cultivated species.
  3. In cotton transfer from wild tetraploid to G.Histirium in which black arm disease resistance occurs.
  4. Cytoplasm transferring. It is used for male sterility transfer. Sterile cytoplasm was present in female parent and recurrent parent used as male parent.
  5. Isogonics lines production.
  6. Conversion of germplasm.

e.g: Photo intensive is produced through backcrossing from sensitive germplasm .In sorghum this is done.

Genetic consequence of Backcrossing:

  • In backcross homozygosity increasing at the same rate as likely to be done in selfing.
  • Like Recurrent Parent the genotype of progeny increases.
  • Selection is used to maintain that gene which is under transferring.
  • Recurrent parent selection for plant is very effective.

Backcross for dominant gene transfer:

  1. One after the other backcross is made.
  2. In each generation of backcross selection of gene transfers.
  3. Backcross which are made usually 5 in numbers.
  4. New variety that is produced was similar to Recurrent Parent.
  5. Dominant Character crosses with those crops which we want to improve.
  6. Introduce a disease resistance which is a actually single transfer into a crop.
  7. Take example of wheat wild type in which actually disease resistance is present crossed with cultivated type of wheat.
  8. Disease resistance act as non recurrent parent or donor parent and cultivated act as recurrent parent.

Example of dominant gene transfer:

  • First original cross of dominant disease resistance cultivar with gene (RR) of donor parent with adapted cultivar A with gene (rr) of recurrent parent.
  • After the original cross the result which produced is shown as

F1=Rr

  • First backcross is done when adapted cultivar A crosses with f1 and result 50% of produced from cultivar A.
  •  2nd backcross cultivar A crosses with backcross1 (BC1) which result in 75% gene produced from cultivar A.
  •  3rd backcross cultivar A crosses with backcross2 (BC2) which result in 87.5% gene produced from cultivar A.
  • 4th backcross cultivar A crosses with backcross3 (BC3) which result in 93.75% gene produced from cultivar A.
  •  5th backcross cultivar A crosses with backcross4 (BC4) which result in 96.87% gene produced from cultivar A.
  •  6th backcross cultivar A crosses with backcross5 (BC5) which result in 98.43% gene produced from cultivar A.
  • 7th backcross cultivar A crosses with backcross6 (BC6) which result in 99.21% gene produced from cultivar A.
  •  8th backcross cultivar A crosses with backcross7 (BC7) which result in 99.60% gene produced from cultivar A.
  •  9th it cultivar A crosses with backcross8 (BC8) which result in 99.80% gene produced from cultivar A.
  •  10th it cultivar A crosses with backcross9 (BC9) which result in 99.90% gene produced from cultivar A.
  •  11th it cultivar A crosses with backcross10 (BC10) which result in 99.95% gene produced from cultivar A.

Self Rr plant from BC10 to obtain plants homozygosity for RR.

Backcross for recessive gene transfer:

  • Due to transfer of gene rust resistance occurs.
  • One after the other backcross is not made.
  • Rust resistance is indentified after the first backcross and every two subsequent backcross so rust resistance is grown on plant.
  • Due to having uniform susceptibility f1 and backcross progenies are not immunize wioth rust resistance and for that of that resistance f2 population is used.
  • Rust resistance (rr) is a variety B and it is a donor or recurrent parent and while agronimally desirable variety A is recurrent parent.

Example of recessive gene:

  1. On first year non recurrent parent B (rr) crosses with recurrent parent A (RR).

F1=Rr

  1. 2nd year f1 backcross to the recurrent parent A (RR) and no resistance test in this.
  •  third year first backcross is made which result in the self pollinated of all plant and no resistance test in this.
  1.  4th year resistance plant is selected and backcross to variety A which result in shown as BC1F2 and rust resistance test occur in this.
  2.  5th year plant backcross to variety A which is shown as BC2 and no resistance test in this occurs.
  3.  6th year self pollinated all plant shown as BC3 and no resistance test in this occurs.
  •  7th year resistance plant selected and backcross to variety A which is shown as BC3F2 and rust resistance test occurs in this.
  •  8th year resistance plant selected and backcross to variety A which is shown as BC4 and no resistance test occurs in this.
  1.  9th year self pollinated all plant which is shown as BC5 and no resistance test occurs in this.
  2.  10th year harvested separately selfed seed and resistance plant selected which is shown as BC5F2 and resistance test occurs in this.
  3.  11th year progenies on plant grown which is shown as BC5F3 and progenies is resistance rust and similar to variety A which is selected.
  •  12th year replicated yield tested with variety A as the check.
  •  13th year distribution for multiplication seed starts.

 Merits of Backcross method:

  1. New variety genotype is similar to that of recurrent parent except gene transfer.
  2. The result of this method is known before and in future reproduce at any time.
  3. In this smaller population is needed.
  4. Not many backcrosses are needed for testing of developed variety because performance of recurrent parent already knows it save 3-4 years time.

Demerits of Backcross method:

  1. Hybridization is require which is usually time taken and costly.
  2. Drag of linkage
  3. New developed is not much unique to recurrent parent except for character transfer.

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