Method of Plant Breeding in Self Pollinated Plants – Pedigree Methods
Mass selection and pure line selection cannot be applied to segregating population. E. g F2, F3 etc. The method is generally used for handling segregation generation may be grouped into three categories.
i) Pedigree Method
ii) Bulk Method
iii) Back Cross Method
The objectives of all these methods are to develop pure line varieties.
In pedigree method, individual plants are selected from F2 and the subsequent generation and their progenies are tested. During the entire operation, a record of the entire parent’s offspring relationship is kept, is known as pedigree record. The selection of individual plant is continued till the progenies show no segregation. At this stage, selection is done among the progenies, because there would be no genetic variation within progenies.
In Pedigree method, a detailed record of the relationship between the selected plants and their progenies is maintained as a result of this each progeny in every generation can be traced back to the F2 plant from which it originated, such record is known as pedigree record or pedigree. The pedigree may be defined as a description of the ancestors of an individual and it generally goes back to some distant ancestors. Thus, it describes the parents grandparents, great grandparents so on of an individual.
Maintenance of Pedigree Record:
Pedigree record may be kept in several ways, but it should be simple and accurate. Generally, each cross is given a number. The first two digits of this number refer to the year in which the cross was made, and the remaining digits denote the serial number of the cross in that year.
For example, the number 7911, denotes the cross number 11 of the year 79. In the segregating generation one of the two systems of designation may be followed.
In this system, the individual plant progenies in each generation are assigned row number, corresponding to their location in the plot. In addition each progeny in F4 and the subsequent generation is assigned the row number of the progeny in the preveious generation from which it was derived.
Progeny in the 7 th row in the F3 plot.
Progeny in the 4 th row in the F4 plot, selected from the progeny in the 7 th row of the F3 plot.
Progeny in the 14 th row in the F5 plot selected from the progeny in the 4 th row of the F4 plot.
Progeny in the 3 rd row in the F6 plot selected from the progeny in the 14 th row of the F5 plot.
Thus each progeny can be traced back to the F3 progeny or F2 plants, from which it originated. But for determining the pedigree of a progeny the breeder has to consult the records of the preveious year.
In this system, in each generation the selected plants are assigned serial numbers within individual progenies. Each progeny or selected plant bear the serial number of all the plants in the preveious generation, related to it by direct descent. Thus, the plants selected in F2 are given serial numbers of their parents ( F2 plants). The plants selected from a progeny in F3 are given the number of that progeny and in each generation the selected plant also given a serial number.
Progeny obtained from plant number 7 selected in F2
Progeny from plant No.4 selected from F3 progeny , derived from the plant No.7 selected in F2
Progeny from plant No.2 selected from the F4 progeny derived from plant no.4 , selected from the F3 progeny, obtained from the plant No.7 selected in F2.
Progeny from plant No 8, selected from the F5 progeny, derived from the plant N0.2 selected from the F4 progeny of the plant No.4 selected from F3 progeny of the Plant No.7 selected in F2.
In this system, the pedigree of a progeny is immediately known and one done not have to refer to the preveious year record. But there are greater chances of error, since more number are to be recorded. In both the systems, the progenies are assigned a different serial number, when they become homozygous and are included in preliminary yield trials. This number is given to those homozygous lines that are included in preliminary yield trials. For keeping a pedigree records following point are important.
1) Only important characteristics should be recorded.
2) Only the promising should be included in the record. Poor progenies may be simply marked discard.
3) The pedigree record must be accurate.
Application of Pedigree Method:
1) Selection of desirable plants from the segregating population in self- pollinated crops.
2) This method is commonly used to correct some specific weaknesses of an established variety (Combination breeding).
3) It is also used in the selection of new superior recombinant type’s i.e Transgressive breeding.
4) This method is suitable for improving specific characteristics such as disease resistant, plant height, maturity etc.