Everything you need to know about the hybridization method used in plant breeding !
Q. 1. What are breeding methods involving hybridization?
Ans. The following breeding methods involve hybridization:
(i) Pedigree breeding method.
(ii) Bulk breeding method.
(iii) Single seed descent method.
(iv) Heterosis breeding, and
(v) Population improvement approaches.
Q. 2. What are uses of hybridization?
Ans. Hybridization is useful in following main ways:
(i) In combining desirable characters from different sources into one genotype.
(ii) In creating vast genetic variability for various economic characters in a population.
(iii) For developing hybrid varieties for commercial cultivation.
(iv) In developing simple varieties,
(v) In transferring desirable gene from wild species to the cultivated one.
Q. 3. Define hybridization.
Ans. Crossing between genetically dissimilar genotypes is called hybridization. After hybridization, the segregating material is handled in three main ways, viz. pedigree method, bulk method and backcross method.
Q. 4. What is pedigree?
Ans. Record of the ancestry of an individual selected plant for its various generations is called pedigree.
Q. 5. What is pedigree breeding?
Ans. A selection procedure which is used in segregating population of self pollinated species, and keeps proper records of plants and progeny selected in each generation is known as pedigree breeding.
Q. 6. What is mass pedigree method?
Ans. It is a modified form of pedigree method in which segregating material is handled by bulk (mass) method when conditions are unfavourable for selection and by pedigree method when conditions are favourable for selection.
Q. 7. Who proposed mass pedigree method?
Ans. Mass pedigree method was proposed by Harrington in 1937 and it was first used by him in cotton.
Q. 8. What are main features of pedigree method?
Ans. Main features of pedigree method are given below:
(i) In self pollinated species, it is used for developing new varieties.
(ii) In cross pollinated species, it is used for developing inbreds.
(iii) Pedigree records are maintained for each selected plant in various generations.
(iv) A variety developed by this method is homozygous and homogenous because it is a progeny of single homozygote.
(v) Selection is based on progeny test (genotypic value).
Q. 9. What are advantages of pedigree method?
Ans. Main advantages of pedigree method are given below:
(i) It offers chances of obtaining transgressive segregants.
(ii) It provides information about mode of inheritance of various qualitative characters.
(iii) The selection is based on genotypic value rather than phenotypic value.
Q. 10. What are demerits of pedigree method?
Ans. Main demerits of pedigree method are given below:
(i) Breeder has to handle huge breeding material which sometimes becomes difficult.
(ii) Breeder has to maintain pedigree records for all selected plants for different generations which take lot of valuable time of the breeder.
Q. 11. What varieties of rice have been developed by pedigree method?
Ans. In rice, varieties Krishna, Ratna, Sabarmati, Padma, Jaya, Bala, Kaveri etc. have been developed by pedigree method.
Q. 12. What varieties of wheat have been developed by pedigree breeding?
Ans. In wheat several varieties such as HD 2281, HD 2285, HD 2380, HD 2402, Janak, Pratap, Raj 2535, DWR 39, WH 331 and WL 616 have been developed by pedigree method.
Q. 13. What are pedigree bred varieties of cotton?
Ans. In cotton several varieties such as LH 900, LH 1556, F 1054, F 1378, HS 6, H 1098, RST 9, Vikas, Khandwa 2, Sharda, Abhadita, Sahana, MCU 9, MCU 11, LRA 5166, Anjali, Surabhi and Suvin have been developed by pedigree method.
Q. 14. What is pedigree bred varieties of chick pea?
Ans. In chick pea, varieties T1, T2, T3, T5 and Radhey are outcome of pedigree breeding.
Q. 15. What is pedigree bred varieties of mungbean?
Ans. In greengram (mungbean), varieties T2, T44, T51 and Sheela have been developed by pedigree method.
Q. 16. What is bulk breeding method?
Ans. A selection method (procedure) used in segregating population of self pollinated species in which material is grown in bulk plots from F2 to F5 with or without selection, next generation is grown from bulk seeds and individual plant selection is practised in F6 or later generations, is known as bulk breeding method.
Q. 17. Who developed the concept of bulk breeding method?
Ans. The concept of bulk breeding method was developed by Nilsson Ehle in 1908.
Q. 18. What is evolutionary method of crop improvement?
Ans. Bulk breeding method leads to significant evolutionary changes in the gene frequencies in a population. Hence, it is also known as evolutionary method of crop improvement.
Q. 19. What are main features of bulk breeding method?
Ans. Main features of bulk breeding method are given below:
(i) It is used in self-pollinated species.
(ii) Natural selection operates during bulking period.
(iii) Selection in final stages is based on progeny test.
(iv) The variety developed by bulk method is homogenous and homozygous,
Q. 20. What are advantages of bulk breeding method?
Ans. Main advantages of bulk breeding method are given below:
(i) It improves adaptation of the population, because natural selection operates during bulking period.
(ii) Chances of getting transgressive segregants are more in this method than pedigree breeding.
(iii) There is no need of maintaining pedigree records.
Q. 21. What are demerits of bulk method?
Ans. Main demerits of bulk breeding method are given below:
(i) Information about mode of inheritance of various oligogenic characters cannot be obtained.
(ii) It takes 2-3 years more for release of a variety than pedigree method of breeding.
(iii) Sometimes, natural selection favours undesirable alleles.
Q. 22. What is the variety of brown mustard developed by bulk breeding method?
Ans. In brown mustard, variety “Narendra Rai” has been developed by bulk breeding method. In USA, more than 50 varieties of self pollinated crops have been developed by this method.
Q. 23. What is single seed descent method?
Ans. A breeding procedure which is used with segregating population of self pollinated species in which plants are advanced by selecting single seed per plant from F2 generation onward is called single seed descent method.
Q. 24. Who developed concept of single seed descent?
Ans. Single seed descent (SSD) method was first suggested by Goulden in 1939 for advancing segregating population of self pollinated species.
Q. 25. What are main features of single seed descent method?
Ans. Main features of SSD method of breeding are given below:
(i) It is used in self pollinated species.
(ii) Artificial selection is practiced,
(iii) It is modified form of bulk breeding method,
(iv) The variety developed by this method is homozygous and homogeneous.
Q. 26. Who first used SSD method in oats?
Ans. In oats, single seed descent method was first used by Grafius in 1965.
Q. 27. Who first used SSD method in soybean?
Ans. In soybean, single seed descent method was first used by Brim in 1966.
Q. 28. What are advantages of SSD method?
Ans. Main advantages of SSD method are given below:
(i) This method requires less space and labour. Hence large number of crosses can be evaluated by this method.
(ii) This is a simple, time saving and less expensive method.
(iii) It retains considerable variability in the population.
Q. 29. What are demerits of SSD method?
Ans. Main demerits of SSD method are given below:
(i) Artificial selection cannot be practised till F5 generation.
(ii) Inheritance of oligogenic characters cannot be studied,
(iii) Transgressive segregants cannot be obtained due to selection of single seed per plant.
Q. 30. What is backcross?
Ans. Crossing of F1 with either of its parents is termed as backcross. When F1 is crossed with its homozygous recessive parent, it is called test cross.
Q. 31. Who coined the term test cross?
Ans. The term test cross was coined by Bridges in 1934.
Q. 32. What is donor parent?
Ans. The parent which donates desirable character is called donor parent. It is also known as non-recurrent parent because donor parent is used only once in the crossing programme.
Q. 33. What is recipient parent?
Ans. The parent which receives a desirable character is known as recipient parent, also called recurrent parent, because it is repeatedly used in backcrossing.
Q. 34. What are main features of backcross method?
Ans. Main features of backcross method are given below:
(i) It is used in both self and cross pollinated species.
(ii) It is used to improve specific character of a well-adapted variety.
(iii) It includes donor and recipient parents in crossing.
(iv) New variety is similar to parent variety except for the character under transfer.
Q. 35. What are basic requirements to start a backcross programme?
Ans. Basic requirements for starting a backcross programme are given below:
(i) A well-adapted variety—deficient in one character.
(ii) A donor parent for desired character.
(iii) High heritability of the character under transfer.
Q. 36. How many backcrosses are required for transfer of oligogenic character?
Ans. Generally, 5-6 backcrosses are sufficient to retain the genotype of original variety with new character.
Q. 37. What are uses of backcross method?
Ans. Backcross method is used for various purposes as given below:
(i) It is used for transfer of oligogenic characters such as disease resistance in cultivated varieties.
(ii) It is used for developing isogenic lines and multiline variety.
(iii) Also used for transfer of male sterility and restorer genes to various agronomic bases.
(iv) Very much useful in interspecific gene transfer.
Q. 38. What are drawbacks of backcross method?
Ans. Main drawbacks of backcross method are given below:
(i) It is more successful for transfer of monogenic and oligogenic characters than polygenic traits.
(ii) It involves crossing work for 5-6 generations.
(iii) Sometimes there is tight linkage between some desirable and undesirable characters which are also transferred alongwith desirable character.
Q. 39. What are cotton varieties developed by backcross technique?
Ans. In cotton, varieties V 797, Digvijay, Vijalpa and Kalyan belonging to Gossypium herbaceum have been developed by backcross method.
Q. 40. What are multilines?
Ans. The deliberate seed mixtures of isolines, closely related lines or unrelated lines are called multiline. Multilines are homozygous but heterogeneous.
Q. 41. Who first suggested use of multilines?
Ans. The use of multilines was first suggested by Jensen in 1952 in oats.
Q. 42. Who outlined method of developing multilines?
Ans. The method of developing multilines was outlined by Borlang and Gibler in 1953.
Q. 43. What are main features of multilines?
Ans. Main features of multilines are given below:
(i) Multilines are relevant to self pollinated species.
(ii) Multilines are homozygous but heterogeneous.
(iii) Multilines are mixtures of several isogenic lines, related lines or unrelated lines.
(iv) Multilines are more adaptable to environmental variations than purelines.
(v) Multilines have broad genetic base than purelines.
Q. 44. What are advantages of multilines?
Ans. There are following two main advantages of multilines:
(i) Multilines have wider adaptability due to genetic diversity.
(ii) They provide better protection from the infestation of new race of a pathogen.
Q. 45. What are drawbacks of multilines?
Ans. Main drawbacks of multilines are given below:
(i) The yield of multilines is lesser than the most productive cultivar of a pureline under disease free conditions. However, reverse is true under adverse conditions.
(ii) The produce of a multiline variety is less uniform and less attractive than that of a pureline.
Q. 46. Give names of multiline varieties of wheat.
Ans. In India, three multiline varieties of wheat viz. KSML 3, MLKS 11 and KML 7404 have been released from PAU, Ludhiana.
Q. 47. How many isogenic lines are mixed to constitute a multiline cultivar?
Ans. Generally 6-10 isogenic lines are mixed together to constitute a multiline cultivar.
Q. 48. Compare pedigree, bulk and backcross methods of breeding.
Ans. Comparison of pedigree, bulk and backcross methods of breeding is presented below in Table 14.1.