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Everything you need to know about self-incompatibility and male sterility in plants !
Q. 1. What is self incompatibility?
Ans. The inability of a plant with functional pollen to set seeds when self pollinated is called self incompatibility. Self incompatibility is classified into two groups, viz. heteromorphic system and homomorphic system.
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Q. 2. Who coined the term self incompatibility?
Ans. The term self incompatibility was coined by stout in 1917. Self incompatibility was first reported in Verbascum phoeniceum by Koelreuter in the middle of 18th century.
Q. 3. What is heteromorphic self incompatibility?
Ans. Self incompatibility due to differences in floral biology is known as heteromorphic self incompatibility. It is of two types, viz. distyly and tristyly.
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Q. 4. What is distyly?
Ans. When style has two positions, viz. low and high with regard to length, it is called distyly.
Q. 5. What is tristyly?
Ans. When the length of style has three positions, viz. low, medium and high, it is known as tristyly.
Q. 6. What is Pin?
Ans. In Primula, flowers with long style and low anthers are referred to as Pin.
Q. 7. What is thrum?
Ans. In primula, flowers with short style and high anthers are called thrum. In primula, crosses are compatible only between style and stamen of matching length i.e. between Pin and Thrum or Thrum and Pin but not between Pin x Pin and Thrum x Thrum.
Q. 8. What is genotype of Pin and Thrum?
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Ans. The Pin is homozygous recessive (ss) and thrum is heterozygous (Ss). A cross between Pin and Thrum produces Pin and Thrum in 1: 1 ratio.
Q. 9. What is homomorphic SI System?
Ans. Presence of self incompatibility due to physiological or genetic causes rather than differences in floral morphology is called homomorphic self incompatibility, It is of two types, viz., gametophytic self incompatibility and sporophytic self incompatibility.
Q. 10. What is gametophytic self incompatibility?
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Ans. Self incompatibility which is controlled by the genetic constitution of gametes is known as gametophytic self incompatibility.
Q. 11. Who first reported gametophytic SI?
Ans. Gemetophytic self incompatibility was first reported by East and Mangelsdorf in 1925 in Nicotiana sanderae.
Q. 12. What are main features of gametophytic system?
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Ans. Main features of gametophytic SI system are given below:
(i) SI is controlled by genetic constitution of pollen.
(ii) SI is governed by a single gene with multiple alleles.
(iii) Alleles show individual action in the style without interaction.
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(iv) The pollen tube growth is usually inhibited in the style or ovary.
(v) It does not exhibit reciprocal differences.
(vi) It permits recovery of male parent only.
(vii) It does not permit production of homozygotes.
(viii) Crosses are of these types, viz. fertile, partially fertile and sterile.
Q. 13. What are crops in which gometophytic SI in found?
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Ans. Gometophytic self incompatibility system has been reported in Red Clover, White Clover, Rye, Potato, Tomato, etc.
Q. 14. What is sporophytic self incompatibility?
Ans. Self incompatibility that is governed by the genotype of pollen producing plant i.e. sporophyte is called sporophytic self incompatibility.
Q. 15. Who first discovered sporophytic SI system?
Ans. The sporophytic self incompatibility system was first discovered by Hughes and Babcock (1950) in Crepis foetida and Gerstel (1950) in Parthenium argentatum (Guayule).
Q. 16. What are main features of sporophytic SI system?
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Ans. Main features of sporophytic self incompatibility system are given below:
(i) SI is controlled by the genotype of pollen producing plant.
(ii) SI is governed by single gene with multiple allele.
(iii) Alleles may show dominance, individual action or interaction either in pollen or style.
(iv) Pollen germination or pollen tube growth is inhibited in the stigma.
(v) Reciprocal differences are observed.
(vi) Recovery of both male and female parent is possible.
(vii) It permits production of some homozygotes
(viii) Crosses are either fully fertile or fully sterile.
Q. 17. What are crops in which sporophytic SI system is found?
Ans. The sporophytic self incompatibility system has been reported in Radish, Cabbage, Cauliflower, etc.
Q. 18. What is monoallelic self incompatibility?
Ans. Self incompatibility which is governed by single gene is called monoallelic self incompatibility. It is found in same species of the family leguminasae, solanaceae and cruciferae.
Q. 19. What is diallelie self incompatibility?
Ans. The SI which is controlled by two genes is called diallelie self incompatibility. It is found in the family Graminae.
Q. 20. What is polyallelic self incompatibility?
Ans. SI which is governed by several genes is known as polyallelic self incompatibility. It is found in sugar-beet.
Q. 21. What are types of SI based on site of gene expression?
Ans. Based on the site of expression of gene, self incompatibility is of three types as follows:
(i) Stigmatic inhibition – It has been reported in radish, cabbage, cauliflower, sunflower etc.
(ii) Stylar inhibition – It is found in sugar-beet, helianthus, Bougainvillea and Fagopyrum.
(iii) Ovarian inhibition – It is found in Narcissus, Lilium, Gasteria, Ribes, Anona etc.
Q. 22. What are the hypotheses to explain mechanism of self incompatibility?
Ans. The following two hypotheses have been proposed to explain the mechanism of self incompatibility:
(i) Complementary hypothesis:
According to this hypothesis, self incompatibility results due to absence of substances in the pistal or poller which are essential for pollen tube penetration.
(ii) Oppositional hypothesis:
According to this hypothesis, interaction between like allele and (S1S2 x S1S2) leads to production of a substance which inhibits the growth of pollen tube in the pistal.
Q. 23. What are ways and means to overcome self incompatibility?
Ans. In crop plants, following ways and means (measures) are used to overcome self incompatibility.
(i) Pollination of immature buds with mature pollen.
(ii) Pollination of aged pistils with incompatible pollen.
(iii) Self pollination at the end of the flowering season.
(iv) Irradiation of style with X-rays before selfing.
(v) Treatment of style with temperature ranging from 30°C to 60°C.
(vi) Removal of stigma in species having stigmatic self incompatibility.
(vii) Placing of pollen in direct contact of ovules.
Q. 24. What is significance of self incompatibility?
Ans. Self incompatibility has great significance in plant breeding. It prevents autogamy and promotes allogomy. It is used for hybrid seed production in Brassica and sunflower. Two self incompatible lines are planted in alternate rows for hybrid seed production. The harvest from both lines would be hybrid seed.
Q. 25. What are types of SI based on flower morphology?
Ans. On the basis of flower morphology, self incompatibility is classified into two types, viz. heteromorphic and homomorphic. Heteromorphic system includes distyly and tristyly and homomorphic system again is of two types, viz. gametophytic system and sporophytic system.
Q. 26. What are types of SI based on genes involved?
Ans. On the basis of gene involved, self incompatibility is of three types, viz. monoallelic, diallelic and polyallelic.
Q. 27. How will you classify SI on the basis of site of expression?
Ans. On the basis of site of gene expression, self incompatibility is of three types, viz. stigmatic, stylar and ovarian.
Q. 28. How will you classify SI on the basis of cytology?
Ans. On the basis of pollen cytology, self incompatibility is of two types as follows:
(i) Binucleate- Pollen grains have two nuclei.
(ii) Trinucleate- Pallen grains have three nuclei.
Q. 29. Who proposed complementary hypothesis of self incompatibility?
Ans. The complementary hypothesis of self incompatibility was proposed by Bateman in 1952.
Q. 30. Who first reported diallelic self incompatibility?
Ans. The diallelic gametophytic self incompatibility was first reported by Lundquist in 1956 in Rye.
Q. 31. How will you identify self incompatibility?
Ans. The self incompatibility can be identified as follows:
(i) If functional pollen grains are unable to fertilize same plant or by absence of seed set by functional pollen on selfing.
(ii) By difference in flower morphology.
Q. 32. In gametophytic self incompatibility what will be the outcome of cross S1S2 x S1S2?
Ans. This cross will be fully incompatible because both the alleles are same female and male parents.
Q. 33. What will be the result of cross S1S2 x S1S3 in gametophytic self incompatibility?
Ans. This cross will be partially fertile because the male parent differs in one allele.
Q. 34. What will be the result when both parents have different alleles (S1S2 x S3 S4) in the gametophytic self incompatibility?
Ans. Such cross is fully compatible and produces four types of progeny, viz. S1S3, S1S4, S2S3 and S2S4.
Q. 35. What is the result of the cross S1S2 x S1S3 in sporophytic self incompatibility?
Ans. This cross will be fully incompatible because in male parent S3 will also behave as S1 due to dominance.
Q. 36. What will be outcome of the cross S2S3 x S1S2 in sporophytic self incompatibility?
Ans. The cross will be fully compatible because S2 also behaves as S1 in male parent due to dominance. This cross will produce four types of progemy viz. S1S2, S2S2, S1S3 and S2S3. Thus one homozygote is also obtained.
Q. 37. What will be outcome of the cross S1S3 x S2S3 in sporophytic self incompatibility?
Ans. The cross is fully compatible because in male parent S3 will also behave as S2 due to dominance. This cross will produce four types of progeny, viz. S1S2, S1S3, S2S3 and S3. This cross permits recovery of both parents S1S3 and S1S3 and also produces one homocygote i.e. S3S3 which is not possible in gametophytic system.
Q. 38. What is male sterility?
Ans. Male sterility refers to condition in which either pollen is absent or nonfunctional in flowering plants. Male sterility is of three types, viz. genetic male sterility, cytoplasmic male sterility and cytoplasmic genie male sterility.
Q. 39. Who first reported male sterility in flowering plants?
Ans. In flowering plants, male sterility was first reported by Koelreuter in 1763.
Q. 40. What is genetic male sterility?
Ans. Pollen sterility which is caused by nuclear genes is called genetic male sterility.
Main features of genetic male sterility are given below:
(i) It is usually governed by recessive genes and rarely by dominant genes.
(ii) In majority of cases, it is governed by single recessive genes. However, sometimes it is governed by two recessive genes.
(iii) The male sterile and fertile plants are observed in 50: 50 ratio. Thus 50% plants are to be rogued out.
(iv) The male sterility is influenced by environmental factors such as low or high temperature.
Q. 41. What is cytoplasmic male sterility?
Ans. Pollen sterility which is governed by cytoplasmic (plasma genes) is called cytoplasmic male sterility.
Main features of CMS are given below:
(i) It is governed by plasma genes.
(ii) It consists of male sterile (A) and male fertile (B) lines.
(iii) It can be used for hybrid seed production in vegetatively propagated crops where grain is not the economic product.
(iv) CMS is not influenced by environmental factors such as low or high temperature.
Q. 42. Who first reported CMS in crop plants?
Ans. Cytoplasmic male sterility was first reported by Welch and Grimball in 1947.
Q. 43. What is cytoplasmic genie male sterility?
Ans. Pollen sterility which is controlled by both cytoplasmic and nuclear genes is called cytoplasmic genie male sterility.
Main features of CGMS are given below:
(i) It is governed by both plasma genes and nuclear genes.
(ii) It consists of three lines i.e. A, B and R lines.
(iii) Male sterility is maintained by crossing it with maintainer line.
Q. 44. Who first reported CGMS in crop plants?
Ans. The cytoplasmic genie male sterility was first reported by Jones and Davis in onion.
Q. 45. What are demerits of genetic male sterility?
Ans. There are two drawbacks of genetic male sterility as given below:
(i) It is influenced by environmental factors. For example, in rice sterile plants become fertile at temperature below 23°C.
(ii) It segregates in 50: 50 fertile and sterile plants in each generation. Hence 50% fertile plants have to be removed.
Q. 46. What are merits of genetic male sterility?
Ans. There are two main advantages of genetic male sterility as follows:
(i) It can be used for hybrid seed production in both seed propagated and vegetatively propagated species.
(ii) It generally does not have undesirable effects.
Q. 47. What are merits of cytoplasmic male sterility?
Ans. Main advantages of CMS are given below:
(i) It is highly stable. It is not influenced by low or high temperature.
(ii) It has only A and B lines and hence requires less area than CGMS system.
Q. 48. What are demerits of cytoplasmic male sterility?
Ans. Main demerits of CMS are given below:
(i) It can be used for development of hybrids only in vegetatively propagated species.
(ii) Sometimes CMS lines have inferior agronomic performance.
Q. 49. What is A line?
Ans. The male sterile line is called A line.
Q. 50. Define B line.
Ans. The male fertile line which is similar to A line except for male fertility is called B line. In other words, it is isogenetic line of A line.
Q. 51. What is R line?
Ans. A line which restores fertility when crossed with cytoplasmic genie male sterile lines is referred to as R line.
Q. 52. What is gynodioecy?
Ans. The co-existence of female (male sterile) and hermaphrodite individuals in a population is known as gynodioecy.
Q. 53. What are male gametocides?
Ans. Chemicals which are used for large scale induction of male sterility in crop plants are called male gametocides or chemical hybridization agents. Such agents include Sodium methyl arsenate, Zinc methyl arsenate, NAA, Gibbrellins, FW 450, Ethrel etc.
Q. 54. What are main drawbacks of male gametocides?
Ans. Main drawbacks of male gametocides are given below:
(i) Pollen abortion is incomplete and erratic.
(ii) The effect is short lived hence repeated application is required.
(iii) Ovule fertility is also adversely affected resulting in low seed setting.
(iv) Male gametocides are expensive.
(v) Male gametocides have adverse effects on plant growth.
Q. 55. What is difference between mutagen induced and gametocide induced male sterility?
Ans. The main difference between mutagen induced male sterility and gametocide induced male sterility is that the former is heritable and the latter is non-heritable.
Q. 56. What are advantages of gametocide induced male sterility?
Ans. Main advantages of gametocide induced sterility are given below:
(i) The sterility can be induced in the same season. It takes 4-5 years to transfer male sterility from one genotype to another by backcross method.
(ii) It is less labourous than backcross method.
(iii) There is no need of maintaining A, B and R lines in this method.
Q. 57. What is transgenic male sterility?
Ans. The male sterility which is induced/developed by the technique of genetic engineering is called transgenic male sterility. Such sterility has been induced in tobacco and rapeseed by transferring a gene from Bacillus amyloliquefaciens.
Q. 58. What are sources of male sterility?
Ans. There are four important sources of male sterility as given below:
(i) Spontaneous mutations
(ii) Induced mutations
(iii) Interspecific crosses, and
(iv) Biotechnology.
Q. 59. How will you identify male sterility?
Ans. Main features of male sterile plants are given below:
(i) Anthers are shrivelled.
(ii) Anthers are smaller than normal.
(iii) Anthers do not contain pollen grains.
(iv) Anthers may contain non-functional (aborted) pollen grains.
Q. 60. Compare self incompatibility and male sterility.
Ans. Comparison of self incompatibility and male sterility is presented in Table 6.1.
Q. 61. Compare gametophytic and sporophytic systems of self incompatibility.
Ans. Comparison of gametophytic and sporophytic system of self incompatibility is presented below in Table 6.2.
Q. 62. Compare genetic male sterility (GMS) and cytoplasmic genie male sterility (CGMS).
Ans. Comparison of GMS and CGMS is presented below in Table 6.3.
