11 pages

Please download to get full document.

View again

of 11
All materials on our website are shared by users. If you have any questions about copyright issues, please report us to resolve them. We are always happy to assist you.
This is the file I made.
  18. Back cross method and various modified methods  Backcross Method In backcross method of breeding, the hybrid and the progenies in subsequent generations are repeatedly backcrossed to one of the parents. As a result, the genotype of the backcross progeny becomes increasingly similar to that of the recurrent parent. The objective of backcross method is to improve one or two specific defects of a high yielding variety. Pre-requisite for back cross breeding 1. A suitable recurrent parent must be available which lacks in one or two characteristics. 2. A suitable donor parent must be available 3. The character to be transferred must have high heritability and preferably it should be determined by one or two genes. 4. A sufficient number of back crosses should be made so that the genotype of recurrent  parent is recovered in full. Application of back cross method This method is commonly used to transfer disease resistance from one variety to another. But it is also useful for transfer of other characteristics. 1. Intervarietal transfer of simply inherited characters E.g. Disease resistance, seed coat colour 2. Intervarietal transfer of quantitative characters. E.g. Plant height, Seed size, Seed shape. 3. Interspecific transfer of simply inherited characters E.g. Transfer of disease resistance from related species to cultivated species. E.g. Resistance to black arm disease in cotton from wild tetraploid species into G.hirsutum 4. Transfer of cytoplasm This is employed to transfer male sterility. The female parent will be having the sterile cytoplasm and recurrent parent will be used as male parent. E.g. Sesamum malabariucum x S.indicum Female parent Recurrent parent.  5. Transgressive segregation Back cross method may be modified to produce transgressive segregants. The F 1  is backcrossed to recurrent parent for 2 to 3 times for getting transgressive segregants. 6. Production of isogenic lines 7.   Germplasm conversion E.g. Production of photo insensitive line from photo Sensitive germplasm through back crossing. This was done in the case of sorghum. Popularly known as conversion programme. Procedure for backcross method The Plan of backcross method would depend upon whether the gene being transferred is recessive or dominant. The plan for transfer of a dominant gene is simpler than that for a recessive gene. First Year Non-Recurrent Recurrent Parent B x Parent A Resistant to rust Susceptible to rust F 1  Rr x rr BC 1  Resistant rr Rr x rr BC 2  rr Rr x rr BC 3 rr Rr x rr BC 4 rr Rr x rr BC 5 Back cross upto 6th or 7 th  generation. After 7 th  BC rust resistant lines are self pollinated. Harvest is done on single plant basis 8 th  Season  Individual plant progenies grown a) Homozygous plants having resistance and resembling parent A are selected harvested and bulked 9 th  season  Yield trials. 10 th  season  Seed multiplication and distribution Steps First Season Hybridization  Crossing between parent B donor (Female) and Susceptible parent A recipient (male) Second Season Raising the F land backcrossed to recurrent parent A. Third season Growing the BC l F l . It will be segregating for 1 susceptible (rr): 1 resistant (Rr). Rust resistant plants are backcrossed with recurrent parent A. This is second backcross. Fourth Season Raising BC 2  F 1  will again segregate in the ratio of 1: 1. Third backcross is done with resistant plants. Fifth Season to Eighth Season Raising backcross F l s and crossing resistant plants with recurrent parent is continued up to 7th backcross Ninth season Raising BC 7 F 1  and observing resistant lines. The plants resembling parent A coupled with resistance is selected and harvested on single plant basis. Tenth Season Growing the progeny row8'and observing each row for resistance. Best rows are selected and harvest is done on row basis Eleventh Season The row bulk is raised in yield trial along with check and the best plots are selected. Twelfth season Selected plot seeds are multiplied and released as new variety.  Back Cross Method - Transfer of Recessive Gene I Season Non recurrent parent B Recurrent parent A Hybridization Resistant Susceptible Rr x RR F 1  Rr II Season Grow the F 1 Rr III Season Grow F2 RR “ Rr “ rr x RR BC 1 IV Season Grow BC 1 F 1 Rr V Season Grow BC 2 F 2  RR : Rr : rr x RR BC 2 VI Season Grow BC 2 F 1  Rr VII Season Grow BC 2 F 2  RR : Rr : rr x RR BC 3 VIII Season Raise BC 3 F 1  IX Season Raise BC 3 F 2  and it will segregate into 1:2:1 with resistant segregant make Backcross 4 (BC 4 ) X Season Do as on VIII Season XI Season do as in IX season Continue this process still 7 th  or 8 th  backcross. After studying 8 th  BCF 2  select plants resembling parent B coupled with resistance. Harvest them on single plant basis. Next season raise them in progeny rows and select beast progenies. Compare them in yield trial and fix the  best culture, multiply it and release it as a variety. While selecting plants artificial bombardment for disease is to be done. Steps I Season: Make a cross between donor parent A and recurrent parent B and Harvest the hybrid. The donor parents A is resistant which is governed by recessive genes. The susceptibility is
We Need Your Support
Thank you for visiting our website and your interest in our free products and services. We are nonprofit website to share and download documents. To the running of this website, we need your help to support us.

Thanks to everyone for your continued support.

No, Thanks

We need your sign to support Project to invent "SMART AND CONTROLLABLE REFLECTIVE BALLOONS" to cover the Sun and Save Our Earth.

More details...

Sign Now!

We are very appreciated for your Prompt Action!