In this article we will discuss about:- 1. Meaning and Features of Pedigree Method 2. Breeding Procedure for Pedigree Method 3. Achievements 4. Merits and Demerits.
Meaning and Features of Pedigree Method:
Pedigree refers to record of the ancestry of an individual selected plant. Pedigree breeding is a method of genetic improvement of self-pollinated species in which superior genotypes are selected from segregating generations and proper records of the ancestry of selected plants are maintained in each generation.
In other words, it is a selection procedure in segregating population of self- pollinated species that keeps proper record of plants and or progeny selected in each generation.
Main features of pedigree method are given below:
1. Application:
This method is widely used for the improvement of self-pollinated species. It is generally used when both the parents that are used in the hybridization have good agronomic characters or are well adapted. Moreover, it is more commonly used for the improvement of polygenic traits than oligogenic characters.
This method is also used in cross pollinated species. In self-pollinated species, it is used for development of new varieties while in cross pollinated species it is used for development of inbred lines. The main difference is that in the self-pollinated species inbreeding occurs naturally while in cross pollinated species inbreeding is done manually.
2. Maintenance of Pedigree Records:
In this method proper record of the ancestry of each selected plant or plant progeny is maintained for all generations of selection. Important characters of each selected plant and progeny are recorded.
3. Selection:
In this method only human selection or artificial selection is used. Natural selection is allowed to operate only in the modified form of pedigree breeding known as mass pedigree method.
It is a modification of pedigree method. It was proposed by Harrington in 1937. Mass pedigree method refers to growing of segregating material by bulk (mass) method when conditions are unfavourable for selection and use of progeny testing (Pedigree method) when conditions are favourable for selection.
The bulk period may vary from one to few generations depending upon the occurrence of favourable conditions. The bulk period is terminated as soon as favourable conditions for selection occur. For example, in wheat dry season is not suitable for selection of straw strength, plant height, earliness and resistance to some diseases and shattering.
Dry seasons occur frequently. Hence breeder has to wait for normal season to make effective selection for above characters in wheat. Similar examples can be cited from many other crops. Harland used mass pedigree method in cotton.
4. Time Taken:
Development of new crop cultivar by this method generally takes 14-15 years.
5. Genetic Constitution:
The variety developed by this method is homozygous and homogeneous, because it is a progeny of single homozygote.
Breeding Procedure for Pedigree Method:
First parents are selected keeping in view the breeding objective. The cross is made between selected parents. The F1 material is grown using wide spacings. The dominance behaviour for various characters is recorded. In F2 also the material is grown using wide spacings.
Individual plant selection is practised in F2. The progeny of each selected plant is grown separately which constitutes F3 generation. In F3 and F4 generations, selection is practised within and between families. From F5 to F8 between progeny selection is practised and superior progeny are identified and isolated in F8.
These progeny constitute strains. These strains are evaluated in replicated multi-location trials for a period of 3-5 years. Based on superior performance, the strain is released as a variety (Fig. 18.1). Thus release of new variety by this method takes 14-15 years.
The number of plants to be grown and selected in each generation is presented in Table 18.1. This is a general procedure of pedigree method. The number of plants to be grown and selected in each generation is not fixed. It may slightly vary from crop to crop.
Achievements of Pedigree Method:
Pedigree method has been extensively used for developing improved varieties in several self- pollinated crops like wheat, rice, pulses, barley, cotton and various vegetable crops.
Some examples are given below:
Rice:
Varieties Krishna, Ratna, Sabarmati, Padma, Jaya, Bala, Kaveri, etc.
Wheat:
HD 2281, HD 2285, HD 2380, ND 2402, Janak, Pratap, Raj 2535 DWR 39, WH 331, WL 616, etc.
Cotton:
LH 900, LH 1556, F 846, F 1054, F 1378, HS 6, H 1098, RST 9, Vikas, Khandwa 3, Sharda, Abhadita, Sahana, MCU 9, MCU 11, LRA 5166, Anjali, Surabhi, Suvin etc.
Pigeonpea:
T21, Prabhat
Greengram:
T2, T44, T51. Sheela, etc.
Chickpea:
T1, T2, T3, T5, Radhey, etc.
Pea:
Pant Matar 2, Jawahar Matar 1, Jawakar Matar 4 etc.
Merits and Demerits of Pedigree Method:
Merits:
1. Pedigree method provides information about the mode of inheritance of various qualitative characters which is not possible by other breeding methods.
2. There are chances of recovering transgressive segregants by pedigree method.
3. This method takes 14-15 years to release a new variety whereas bulk method takes much longer time (15-16 years).
4. The breeding value of selected plants is ascertained by progeny test. Thus pedigree selection is based on genotypic value rather than phenotype value.
Demerits:
1. The selected material becomes so large that handling of the same becomes very difficult.
2. Records have to be maintained for all the selected plants and progeny which take lot of valuable time of a breeder.
3. Since large numbers of progeny are rejected in this method, there are chances of elimination of some valuable material.
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