Everything you need to know about the introduction and selection methods of plant breeding !
Q. 1. What are breeding methods?
Ans. Various procedures (selections, hybridization, mutation, etc.) which are used for genetic improvement of crop plants are known as breeding methods.
Q. 2. How will you classify plant breeding methods?
Ans. Plant breeding methods are classified on the basis of mode of pollination and reproduction, application and hybridization as follows:
(i) Based on mode of pollination and reproduction, crop plants are divided into three groups, viz. self pollinated species, cross pollinated species and asexually propagated species. Their breeding methods differ to some extent, though some methods are common.
(ii) Based on applications, breeding methods are of three types, viz.:
(a) General breeding methods,
(b) Special breeding methods, and
(c) Population improvement approaches.
(iii) Based on hybridization, breeding methods are classified into two broad groups as follows:
(a) Methods which involve hybridization such as pedigree, SSD, bulk and backcross breeding, heterosis breeding, population improvement approaches and molecular breeding.
(b) Methods which do not involve hybridization such as Introduction, Mass selection, Progeny selection, Pureline selection, Clonal selection, Mutation breeding and Transgenic breeding.
Q. 3. What are methods of breeding self-pollinated crops?
Ans. In self pollinated species, the following breeding methods are used:
(i) Plant Introduction
(ii) Pureline selection
(iii) Mass selection
(iv) Pedigree method
(v) Bulk Breeding method
(vi) Single Seed Descent
(vii) Heterosis breeding
(viii) Mutation breeding
(ix) Polyploidy breeding
(x) Transgenic breeding
(xi) Molecular breeding etc.
Q. 4. What are methods of breeding cross pollinated crops?
Ans. In cross pollinated crops, following breeding methods are used:
(i) Plant introduction
(ii) Mass and Progeny selection
(iii) Heterosis breeding
(iv) Synthetic breeding
(v) Composite breeding
(vi) Backcross method
(vii) Polyploidy breeding
(viii) Transgenic breeding
(ix) Molecular breeding etc.
Q. 5. What are methods of breeding asexually propagated species?
Ans. In asexually propagated species, following breeding methods are used:
(i) Plant introduction
(ii) Clonal selection
(iii) Heterosis breeding
(iv) Mutation breeding
(v) Polyploidy breeding
(vi) Backcross method
(vii) Distant hybridization
(viii) Transgenic breeding
(ix) Molecular breeding.
Q. 6. What are breeding methods which are common for self pollinated, cross-pollinated and asexually propagated crops?
Ans. The following breeding methods are used for genetic improvement of all three groups of crop plants:
(i) Plant introduction
(ii) Backcross method
(iii) Heteroses breeding
(iv) Polyploidy breeding
(v) Transgenic breeding
(vi) Molecular breeding.
Q. 7. What are general breeding methods?
Ans. Various breeding approaches that are more commonly used for genetic improvement of crop plants are known as general breeding methods.
They are listed below:
(i) Plant introduction
(ii) Pureline selection
(iii) Mass selection
(iv) Progeny selection
(v) Synthetic and composite breeding etc.
(vi) Pedigree Method
(vii) Bulk method
(viii) Backcross method
(ix) Heterosis breeding.
Q. 8. What are special breeding methods?
Ans. Those breeding methods that are rarely or less commonly used for crop improvement are known as special breeding methods.
Such methods are listed below:
(i) Mutation breeding
(ii) Polyploidy breeding
(iii) Transgenic breeding
(iv) Molecular breeding.
Q. 9. What are breeding methods which do not involve hybridization?
Ans. The following breeding methods do not involve hybridization:
(i) Plant introduction
(ii) Pureline selection
(iii) Mass selection
(iv) Progeny selection
(v) Mutation breeding
(vi) Clonal selection
(vii) Transgenic breeding.
Q. 10. What is plant introduction?
Ans. Plant introduction refers to transposition of crop plants from the place of their cultivation to such areas where they were never grown earlier. It is of two types, viz. direct introduction and indirect introduction.
Q. 11. What is direct introduction?
Ans. Introductors which are immediately adapted to the changed environment are called direct introductions.
Q. 12. What is indirect introduction?
Ans. Introductions which require few years for adaptation are known as indirect introductions.
Q. 13. What is primary introduction?
Ans. Introduction that can be used for commercial cultivation without any change in the original genotype is called primary introduction.
Q. 14. What is secondary introduction?
Ans. Introduction that can be used as a variety after selection from the original genotype or used for transfer of some desirable genes to the cultivated variety is known as secondary introduction.
Q. 15. What is exotic variety?
Ans. A foreign variety which is directly recommended for cultivation is called exotic variety.
Q. 16. What are examples of primary introduction?
Ans. Examples of primary introduction in wheat and rice are given below:
(i) Wheat: Sonora 64 and Lerma Rojo.
(ii) Rice: Taichung Native 1, IR 8, IR 20 and IR 36.
Q. 17. Cite examples of secondary introduction.
Ans. Examples of secondary introduction are given below:
(i) Wheat:
Kalyan sona and Sonalika. These varieties were released after selection from the material received from Mexico.
(ii) Cotton:
PRS 72, SB 289 E, American Nectariless etc. Many such examples can be cited from other field crops.
Q. 18. How plants were introduced earlier?
Ans. Earlier plants used to be introduced through travellers, traders, invaders and merchants.
Q. 19. How plants are collected now?
Ans. Now plants are introduced/collected by specific organizations at international and national level:
(i) At international level, crop plants or germplasms are collected by International Plant Genetic Resources Institute (IPGRI), Rome, Italy.
(ii) In India germplasm collections are made by following organizations:
(a) National Bureau of Plant Genetic Resources (NBPGR), New Delhi.
(b) Forest Research Institute (FRI), Dehradun.
(c) Botanical Survey of India (BSI), Kolkata.
Q. 20. What are means of Plant Introduction?
Ans. Plant material is collected by following methods (ways):
(i) Through expeditions
(ii) Through personal visit
(iii) Through correspondence
(iv) By exchange of material
(v) By purchase, and
(vi) As a gift.
Q. 21. What are purposes of plant introduction?
Ans. Main purposes of plant introduction are given below:
(i) To use as new source of food, vegetable, fibre fruit, timber plant etc.
(ii) For conservation of biodiversity.
(iii) For genetic improvement of crop plants.
(iv) For aesthic interest—flowering plants.
(v) For study of origin and evolution of crop plants.
Q. 22. What are sources of plant collections?
Ans. Important sources of plant collections are given below:
(i) Centres of diversity
(ii) Gene banks
(iii) Gene sanctuaries
(iv) Seed companies
(v) Farmers fields
(vi) Markets.
Q. 23. What are uses of Plant introduction?
Ans. The introduced plant material can be used in following main ways:
(i) It can be used directly as a variety.
(ii) As a new variety after selection.
(iii) As a parent in developing new hybrids.
(iv) As a parent in hybridization for developing new crop cultivars.
Q. 24. What are advantages of Plant introduction?
Ans. Main advantages of plant introduction are given below:
(i) It is useful in introducing new crop plants.
(ii) It helps in conserving plant biodiversity.
(iii) It is useful in protecting those species that are threatened by danger of extinction.
(iv) It is a simple and rapid method of crop improvement.
(v) It is applicable to all crops i.e. self pollinated, cross pollinated and asexually propagated species.
Q. 25. What are demerits of Plant introduction?
Ans. The main demerit of plant introduction is that sometimes new (a) diseases, (b) insects, and (c) weeds get entry in the country alongwith introduced material.
Q. 26. What are the crops introduced in India from other countries?
Ans. Various, important crops such as maize, potato, tomato, brinjal, groundnut, papaya, pineapple, triticale etc. have been introduced in India from other countries.
Q. 27. What is domestication?
Ans. The process- of bringing wild and weedy species under human management is called domestication.
Q. 28. What is acclimatization?
Ans. Adaptation of an introduced variety to the new environment is known as acclimatization.
Q. 29. What is selection?
Ans. The process which favours survival and further propagation of some plants having more desirable characters than others is called selection. It is of two types, viz. natural and artificial.
Q. 30. What is natural selection?
Ans. Selection which operates in nature without human interference is called natural selection. It favours those plant characters which are essential for survival (adaptation) of a species.
Q. 31. What is artificial selection?
Ans. Selection made by human is called artificial selection. It favours those characteristics of plants which are related to yield and quality.
Q. 32. What are different types of artificial-selection?
Ans. Artificial selections are of different types as given below:
(i) Mass selection
(ii) Pureline selection
(iii) Progeny selection
(iv) Clonal selection
(v) Recurrent selection
(vi) Directional selection
(vii) Disruptive selection
(viii) Stabilizing selection.
Q. 33. Who coined the term Selection?
Ans. The term selection was coined by Darwin in 1858.
Q. 34. What is pureline?
Ans. Progeny of a self pollinated homozygous plant obtained by selfing is called pureline.
Q. 35. Who coined the term pureline?
Ans. The term pureline was first used by Johannsen in 1903.
Q. 36. Who coined terms genotype and phenotype?
Ans. Terms genotype and phenotype were coined by Johannsen in 1909.
Q. 37. Who developed the concept of pureline theory?
Ans. The concept of pureline theory was developed by Johannsen in 1926 working with Princess Variety of common bean (Phoseolus vulgaris).
Q. 38. What are main features of purelines?
Ans. Main features of purelines are given below:
(i) Purelines are homozygous and homogeneous.
(ii) Purelines are relevant to self pollinated crops.
(iii) Purelines are highly uniform.
(iv) There is no heritable variation in a pureline variety.
(v) Purelines have narrow genetic base.
(vi) Purelines have narrow adaptation.
Q. 39. What are sources of variation in a pureline variety?
Ans. Main sources of variation in a pureline variety are given below:
(i) Natural outcrossing
(ii) Spontaneous mutations and
(iii) Mechanical admixtures.
Q. 40. Why purelines have poor adaptability?
Ans. Purelines have pure adaptability due to narrow genetic base.
Q. 41. Why a pureline variety is more prone to the attack of new disease?
Ans. A pureline variety is more prone to the attack of new race of a pathogen due to genetic uniformity and narrow genetic base.
Q. 42. What is pureline selection?
Ans. Development of a new variety through identification and isolation of a single best plant progeny from mixed population of self pollinated species is called pureline selection.
Q. 43. What are advantages of pureline selection?
Ans. Advantages of pureline selection are as follows:
(i) It helps in isolating best genotypes for disease resistance, insect resistance, yield, quality- earliness etc. from a mixed population of an old variety.
(ii) Pureline varieties are uniform and more attractive than mass selected varieties.
(iii) This is an easy and cheap method of crop improvement.
Q. 44. What are demerits of pureline selection?
Ans. Main demerits of pureline selection are given below:
(i) Pureline varieties have danger of uniformity.
(ii) Pureline varieties have narrow genetic base.
(iii) Pureline varieties have narrow adaptation.
Q. 45. What steps are involved in development of a pureline variety?
Ans. Pureline selection consists of following steps:
(i) Selection of a heterogeneous material as base population.
(ii) Isolation of purelines by individual plant selection.
(iii) Evaluation of purelines in field trials.
(iv) Release of the best pureline as a variety.
Q. 46. What is mass selection?
Ans. A method of crop improvement in which individual desirable plants are selected on the basis of phenotype from a mixed population, their seeds are bulbed and used to grow next generation is called mass selection. It is of two types, viz. positive and negative.
Q. 47. What is positive mass selection?
Ans. Selection of desirable plants from a mixed population and growing of next generation from the bulk seed of selected plants is called positive mass selection.
Q. 48. What is negative mass selection?
Ans. Removal of off type plants from a mixed population and allowing rest of the plants further is called negative mass selection.
Q. 49. Who proposed grid method of mass selection?
Ans. The grid method of mass selection was suggested by Gardner in 1962.
Q. 50. What are main features of mass selection?
Ans. Main features of mass selection are given below:
(i) It is applicable to both self and cross-pollinated species.
(ii) In self pollinated species, mass selected varieties are homozygous but heterogeneous (mixture of several purelines).
(iii) Mass selected varieties have broad genetic base and wide adaptaion than purelines.
(iv) Mass selected varieties have heritable variation.
(v) The produce of mass selected varieties is lesser uniform than that of pureline varieties.
(vi) Mass selected varieties are less prone to the attack of new race of a pathogen due to genetic diversity.
Q. 51. What are main drawbacks of mass selection?
Ans. Main drawbacks of mass selection are given below:
(i) The selection is based on phenotype which is not always indication of a superior genotype.
(ii) In cross pollinated species, there is no control on the pollination. Selected plants are pollinated by both superior and inferior pollen parents.
(iii) The produce of mass selected variety is lesser uniform than that of pureline variety.
Q. 52. What are modifications of mass selection?
Ans. The following modifications of mass selection have been suggested by various workers:
(i) Rejection of inferior pollen parents,
(ii) Use of composite pollen for pollinating selected plants,
(iii) Gardner (1962) suggested stratified method of mass selection in which field is divided into small; plats and 40-50 superior plants are selected in each plot. It reduces the effect of soil heterogeneity.
Q. 53. What is progeny selection?
Ans. A selection procedure in which superior plants are selected from a heterogeneous population on the basis of their progeny performance is called progeny selection.
Q. 54. What is progeny test?
Ans. The test of genotypic value of an individual based on performance of its progeny is called progeny test.
Q. 55. Who suggested progeny test?
Ans. Progeny test was first suggested by Louis de Vilmorin. It is also known as Vilmorin principle.
Q. 56. What is a clone?
Ans. Progeny of a single vegetatively propagated plant obtained by asexual reproduction is called clone.
Main features of a clone are given below:
(i) The progeny of a clone is homogenous but heterozygous.
(ii) Selfing of a clone leads to high inbreeding depression.
(iii) Heterosis can be easily conserved in clonally propagated crops.
(iv) The progeny of a clone has wider adaptability due to heterozygosity.
Q. 57. What are sources of variation in a clone?
Ans. Main sources of variation in a clone are given below:
(i) Bud mutations
(ii) Mechanical mixture, and
(iii) Occasional sexual reproduction.
Q. 58. What is clonal selection?
Ans. A procedure of selecting superior clones from the mixed populations of asexually propagated crops such as sugarcane, potato etc. is called clonal selection.
Q. 59. Who coined the term clone?
Ans. The term clone was first used by Webber in 1903.
Q. 60. Why clones are more prone to new race of a pathogen?
Ans. Clones are more prone to the incidence of new race of a pathogen due to uniformity (homogenous nature).
Q. 61. Why a cross between two clones exhibit segregation in F1?
Ans. Clones are heterozygous, hence F1 generation of a cross between two clones exhibits segregation.
Q. 62. Compare a pureline and a clone.
Ans. Comparison of a pureline and a clone is presented below in Table 13.1.
Q. 63. Compare mass selection and pureline selection.
Ans. Comparison of mass selection and pureline selection is presented below in Table 13.2.
