Everything you need to know about distant hybridization of plant species !
Q. 1. What is distant hybridization?
Ans. Crossing between different species of the same genes or different genera of the same family is called distant hybridization; also known as wide crossing. It is of two types, viz. interspecific hybridization and intergeneric hybridization.
Q. 2. What is interspecific hybridization?
Ans. Crossing between two different species of the same genus is termed interspecific hybridization or intra-generic hybridization. Such crosses are called interspecific crosses and progeny of such cross is called interspecific hybrid.
Q. 3. Who first used interspecific hybridization?
Ans. Interspecific hybrid was first developed by Thomas Fairchild in 1717 between sweet William and carnation species of Dianthus (Dianthus barbatus x D. Canyophyllus).
Q. 4. When will you use interspecific hybridization?
Ans. Interspecific hybridization is used when the desirable character is not found within the species of a crop.
Q. 5. What are types of interspecific crosses?
Ans. Interspecific crosses are of following three types:
(i) Fully fertile crosses – Such crosses are obtained between those species which have complete chromosome homology.
(ii) Partially fertile crosses – Such crosses are obtained between those species which differ in ploidy level but have some chromosomes in common.
(iii) Fully sterile crosses – Such crosses are obtained between those species which do not have chromosome homology.
Q. 6. What is intergeneric hybridization?
Ans. Crossing between two genera of the same family is called intergeneric hybridization. Triticale and Raphanobrassica are outcome of intergeneric crosses.
Q. 7. What is introgression?
Ans. Transfer of some genes from one species into the genome of another species is called introgression.
Q. 8. Who coined the term Introgression?
Ans. The term introgression was first used by Anderson and Hubricht in 1938.
Q. 9. Who made first cross between wheat and rye?
Ans. The first intergeneric cross between bread wheat and rye was made by Rimpu in 1890 in Sweden.
Q. 10. Who made first intergeneric cross between radish and cabbage?
Ans. The first intergeneric cross between radish and cabbage was made by Karpechenko in 1928 in Russia.
Q. 11. What are parents of Raphanobrassica?
Ans. The parents of Raphanobrassica are radish (Raphanus stativus) and cabbage (Brassica oleracea).
Q. 12. What are basic diploid species of Brassica?
Ans. Following are three basic diploid species of Brassica:
(i) Rapeseed (Brassica campestris 2n = 20, AA)
(ii) Black mustard (Brassica nigra 2n = 16, BB)
(iii) Cabbage (Brassica oleracea 2n = 18, CC)
Q. 13. What are three tetraploid species of Brassica?
Ans. Three tetraploid species of Brassica are given below:
(i) Brassica juncea (2n = 32, AABB)
(ii) Brassica carinata (2n = 34, BBCC)
(iii) Brassica napus (2n = 38, AACC)
Q. 14. Who proposed origin of tetraploid species of Brassica?
Ans. The origin of tetraploid species of Brassica was proposed by Nagaharu U in 1935 using a triangle which is popularly known as U’s triangle.
Q. 15. Who first synthesized amphidiploid in cotton?
Ans. Harland (1940) made a cross between Gossypium arboreum and G. thurberi and synthesized an amphidiploid which was similar to upland cotton (G. hirsutum).
Q. 16. Who traced genetic origin of upland cotton?
Ans. Phillips (1963) based on morphological and cytological studies, reported that Gossypium hirsutum (upland cotton) has originated from a cross between G. africanum (AA) and G. raimondii (DD).
Q. 17. Who traced genetic origin of bread wheat?
Ans. McFadden and Sears (1947) reported that Triticum turgidum and T. tauchi are involved in the evolution of bread wheat (T. aestivum).
Q. 18. Who synthesized Nicotiana digluta species of tobacco?
Ans. The new species Nicotina digluta of tobacco was synthesized by Clausen and Good speed in 1925 from a cross between N. tabacum and N. glutinosa.
Q. 19. Who traced origin of Nicotiana tabacum?
Ans. The origin of cultivated tobacco (Nicotiana tobacum) was traced by Goodspeed and Clausen in 1928. They established that cultivated tobacco- (N. tabacum) is amphidiploid between N. sylvestris and N. tomentosa.
Q. 20. What are progenitors of Nicotiana rustica?
Ans. Goodspeed and Clausen (1928) established that Nicotiana rustica is an amphidiploid between N. paniculata and N. undulata.
Q. 21. What are main barriers of distant hybridization?
Ans. The main barriers of distant hybridization are:
(i) Cross incompatibility
(ii) Hybrid inviability
(iii) Hybrid sterility, and
(iv) Hybrid breakdown.
Q. 22. What is cross incompatibility?
Ans. Inability of the functional pollen of one species or genus to effect fertilization of female gametes of another species or genus of the same family is known as cross incompatibility.
Q. 23. What is hybrid inviability?
Ans. Inability of a hybrid zygote to grow into a normal embryo under normal conditions of development is known as hybrid inviability.
The main reasons of hybrid inviability are given below:
(i) Unfavourable interaction between chromosomes of two species.
(ii) Dishormony between cytoplasm and nuclear genes, and
(iii) Unfavourable interaction among embryo, endosperm and maternal tissues.
Q. 24. What the reasons are of cross incompatibility?
Ans. Main reasons of cross incompatibility are given below:
(i) Lack of pollen germination.
(ii) Insufficient growth of pollen tube to reach ovule, and
(iii) Inability of male gamete to unite with egg cell.
Q. 25. How will you overcome problem of hybrid inviability?
Ans. Following techniques can be used to overcome the problem of hybrid inviability:
(i) Proper choice of parents
(ii) Making reciprocal crosses
(iii) Application of growth hormones
(iv) Transfer of embryo to culture medium.
Q. 26. What is hybrid sterility?
Ans. Inability of a hybrid to produce viable offspring is called hybrid sterility. The problem of hybrid sterility is more acute in intergeneric crosses than in interspecific crosses. The main cause of hybrid sterility is lack of structural homology between the chromosomes of two species. This can be overcome by chromosome doubling.
Q. 27. What is cryptic structural hybridity?
Ans. In interspecific hybrids, sometimes sterility is due to small structural changes in chromosomes which are not detectable during meiosis. Stebbins termed it as cryptic structural hybridity.
Q. 28. Who coined the term cryptic structural hybridity?
Ans. The term cryptic structural hybridity was coined by stebbins in 1958.
Q. 29. What is hybrid breakdown?
Ans. A condition in which F1 plants of an interspecific cross are vigorous and fertile but their F2 progeny is weak and sterile is called hybrid breakdown.
It may result due to following reasons:
(i) Linkage of dominant genes in one species and recessive in other species.
(ii) Small structural differences in the chromosomes of two species.
Q. 30. What is alien addition?
Ans. Addition of one chromosome of wild species to the normal complements of a cultivated species is known as alien addition.
Q. 31. What is alien addition line?
Ans. A line having one chromosome of wild species to its somatic chromosome complements is called alien addition line.
Q. 32. Who coined the term alien addition?
Ans. The term alien addition was coined by Leighty and Taylor in 1924.
Q. 33. What is alien substitution?
Ans. Replacement of one pair of chromosomes of cultivated species with those of wild donor species is known as alien substitution.
Q. 34. What is alien substitution line?
Ans. A line in which one pair of chromosome is from wild donor species is called alien substitution line.
Q. 35. Who coined the term alien substitution?
Ans. The term alien substitution was first used by Kattermann in 1938.
Q. 36. How will you make wide crosses successful?
Ans. The following techniques are useful in making distant crosses successful:
(i) Selection of compatible parents
(ii) Making reciprocal crosses
(iii) Manipulation of ploidy level
(iv) Making bridge crosses
(v) Use of pollen mixtures
(vi) Use of growth regulators (hormones)
(vii) Use of embryo rescue technique
(viii) Use of protoplast fusion technique
(ix) Cutting of long style to proper size etc.
Q. 37. What is the role of wide crossing in crop improvement?
Ans. Distant hybridization has played significant role in the improvement of crop plants for various characters as follows:
(i) Imparting disease and insect resistance
(ii) Improvement in quality
(iii) Improvement in adaptation
(iv) Improvement in yield
(v) Development of interspecific hybrids
(vi) Development of new crop species etc.
Q. 38. What are main limitations of wide crossing?
Ans. Main limitations of wide crossing are given below:
(i) Cross incompatibility, hybrid inviability, hybrid sterility and hybrid breakdown.
(ii) Linkage of some undesirable genes with desirable one.
(iii) It is a long term programme.
Q. 39. What is somatic hybridization?
Ans. Crossing of plants through fusion of somatic cells, i.e. protoplasts is called somatic hybridization.
Q. 40. Who coined the term somatic hybridization?
Ans. The term somatic cell hybridization was coined by Barski et al. in I960.
Q. 41. What is protoplast?
Ans. Naked cells or cells without cell wall are referred to as protoplasts.
Q. 42. Who coined the term protoplast?
Ans. The term protoplast was first used by Hanstein in 1880.
Q. 43. What is bridge cross?
Ans. A cross which involves third species (which is compatible with both species) to make gene transfer possible between two cross incompatible species are called bridge cross.
Q. 44. What is bridging species?
Ans. A species which can cross with both cross incompatible species and is used to make bridge between such species is called bridging species.
Q. 45. What are varieties of cotton developed through interspecific hybridization?
Ans. Varieties of upland cotton developed through interspecific hybridization include MCU 2, MCU 5, Deviraj, Devitej, Khandwaj 1, Khandwa 2, Bodnawar 1. PKV 081, PKV Rajat, and Arogya.
Q. 46. What are interspecific tetraploid hybrids of cotton?
Ans. In cotton several interspecific tetraploid hybrids have been released for commercial cultivation in India. Such hybrids include Varalaxmi, JKHY 11, CBS- 156, DCH 32, NHB 12, TCHB 213, DHB 105, NHB 302, Sruthi etc.
Q. 47. What are interspecific diploid cotton hybrids?
Ans. In diploid cotton, some interspecific hybrids have been released for commercial cultivation in India. Such hybrids include DH 7, DH 9, DDH 2 and Pha 46.
Q. 48. What are differences between interspecific and intergeneric hybridization?
Ans. Main differences between interspecific and intergeneric hybridization are presented below in Table 21.1:
