Breeding of Vegetable, Spice and Tuber crops (2+1)

Backcross -Recessive gene transfer

• Backcross -Recessive gene transfer

• How Recessive Gene is transferred through Backcross Breeding?
• Let, variety X is well adapted and high yielding variety.
• Variety Y is another variety resistant to a specific disease; which is governed by a recessive gene. We wish to transfer this recessive gene form variety Y to variety X.
• So, variety X – recurrent parent (♀)Variety Y – donor parent (♂)
• When the desired character i.e. disease resistance is governed by a recessive gene, back crosses cannot be performed in continuation as in dominant gene transfer method. After first back cross and then after every two subsequent back crosses F2 must be raised to test rust resistance. Only F2 is tested for resistance as all F1 and back cross progenies are heterozygous and susceptible to disease.
• The various steps for this backcross breeding are as follows

 
• Hybridization – The two varieties X and Y are crossed. Generally recipient / recurrent variety is used as female parent.
• F1 generation – F1 plants are back crossed with the variety X.
• BC1 generation –As disease resistance is controlled by recessive gene all the plants will be susceptible to disease, so disease resistance is not tested for this generation. Plants raised from seeds of above cross are selfed.
• BC1 F2 generation – Test for disease resistance is conducted. Resistant plants which are similar in plant characteristic to recurrent parent are selected and back crossed with recurrent parent.
• BC2 generation – Plants are grown from seeds of above cross, plants those are similar in plant characteristic to recurrent parent are selected and backcrossed with recurrent parent. Resistance test is not conducted.
• BC3 generation – Plants are selfed to grow F2. Resistance test is not conducted for the sake of selection; it is done on the basis of resemblance to variety.
• BC3 F2 generation – Selection for resistance is conducted and selected plants are back crossed with variety X.
• BC4 generation – Back cross of plants selected above with recurrent parent. Disease resistance test is not conducted.
• BC5 generation – Plants are selfed to raise F2. Disease resistance test is not conducted in this generation.
• BC5 F2 generation – Disease resistant plants similar in plant characteristics to recurrent variety are selected. Selfed and seeds are harvested separately.
• BC5 F3 generation – Individual plant progenies are grown. Selection is done for disease resistance and resemblance to variety X. Seeds of selected plants are bulked to constitute the new variety.
• Yield trials – Replicated yield trials are conducted with variety X as a check. The newly constituted variety should be similar to variety X for most of the important characteristics. Seeds are multiplied for distribution.