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- 1. Lecture 26 .Genetic characters of asexual reproduction – breeding methods – clonal selection – hybridization and clonal selection – merits and demerits – achievements; Chimeras and its types; Tree breeding – clonal orchards.
- 2. Some Agricultural and a large number of horticultural crops are asexually propagated Eg. Sugarcane, Potato, sweet potato, colocassia, mentha, ginger, turmeric, banana Almost all fruit trees – Mango, citrus, apples,pears,peaches, litchi Many ornamentals and grasses.
- 3. Characteristics of Asexually propagated crops Majority of them perennials –sugarcane, fruit trees etc. annual crops mostly tuber crops potato, sweet potato, cassava Many ofthem show reduced flowering and seed set They were invariabily cross pollinated Highly heterozygous and show severe inbreeding depression Majority of them are polyploids eg. Potato, sugarcane Many species are interspecific hybrids eg. Sugarcane, banana, Rubus These crops consist of large number of clones
- 4. Breeding methods in vegetatively propogated crops The vegetatively propagated crops can be improved by using following techniques. 1. Clonal selection. 2. Hybridisation & Selection a) Inter varietal b) Inter specific 3. Polyploidy breeding 4. Mutation breeding 5. Tissue culture and anther culture
- 5. clone A clone is a group of genetically uniform plants produced from a single plant through asexual reproduction Phenotypic differences within a clone not genetical but due to environment
- 6. Characteristics of a clone Obtained through asexual reproduction Genotype maintained indefinitely without variation Phenotypic variation is only due to environment Contd…
- 7. Clones degenerate due to viral or bacterial infections Clone sometimes become extinct due to its susceptibility to diseases or insect pests Genetic variation may arise Clones are highly heterozygous Show severe loss in vigour due to inbreeding
- 8. Genetic variations in clones 1. Mutation Somatic mutations also known as bud mutation Only dominant mutations would be expressed in the somatic tissues because of heterozygous conditions Recessive mutants are expressed only in homozygous conditions Contd…
- 9. 2. Mechanical mixture Mechanical mixture produces genetic variations within a clone 3. Sexual reproduction Seedlings genotypically different due to segregation
- 10. Clonal degeneration Loss in vigour and productivity of clones over time is known as clonal degeneration Degeneration is inherent Clonal degeneration may result from mutation and diseases
- 11. Clonal selection Phenotypic value is due to its genotype (G), environment (E) and genotype x environment interaction (GE) G effects are heritable and stable A selection for polygenic characters like yield should not be based on single plant observation Contd…
- 12. Replicated yield trails help in assessing yield potential of clone Plant height, days to flowering, color, disease resistance – highly heritable and selections based on single plant.
- 13. I year Select plants of superior clones II year Evaluate selected clones separately – select desirable clones III year Preliminary yield trial with suitable check and selected outstanding clones IV year to VIII year Multilocation trial with standard checks and release of superior clones as new varieties IX year Superior & outstanding clones released as new variety, large scale multiplication Steps in clonal selection
- 14. Merits of clonal selection Only method of selection to clonal crops Preserves the gene combinations and avoid inbreeding depression Combined with hybridization to generate the necessary variability Useful in maintaining the purity of clones
- 15. Demerits of clonal selection Utilizes the natural variability Not devised to generate variability Sexual reproduction is necessary for the creation of variability
- 16. Hybridization & Selection in asexually propagated species I year II year III year IV year Hybridise selected clones Plant seedlings derived & select superior plants Evaluate selected clones with suitable checks Select superior clones Preliminary yield trial with suitable check & selection of outstanding clones V year to IX year Multilocation trial with appropriate checks & release of superior clones as new varieties Superior & outstanding clone released as new variety Large scale multiplication X year
- 17. Interspecific hybridisation in the improvement of clonal crops Inter Specific hybridization Successfully used in many crops like Rubus, Malus Strawberries. Potato variety Kufri Kuber was developed from a complex cross. (S. Cuttilobum) x (S.tuberosum) x S.andigena Generally interspecific crosses are useful for disease resistance. For E.g. S.demissum has been extensively used to induce late blight resistance in potato.
- 18. Sugar cane : All varieties of sugar cane now in cultivation have been developed from complex cross between S.officinarum, S.barberi, S. robustum and S.spontaneum The success of interspecific hybridization in clonal crops are due to following reasons. i. Due to asexual: reproduction there is no segregation. ii. Most of them are not seed crops and hence flowering and fertility are not essential for their success.
- 19. Achievements-clonal selection Kufri red potato is clonal selection from Darjeeling red round Kufri safed Potao is clonal selection from the potato variety Phulwa. Bombay green banana is a bud selection from dwarf Cavendish High Gate banana bud selection from Gross michel
- 20. Achievements-Hybridization Potato varieties developed through hybridisation Kufri Alannkar, Kufri kuber, Kufri kundhan, kufri sindhuri, kufri chandramuki, kufri chamatkar Kufri jyoti is late blight resistant Kufri sheetman is frost resistant Sugarcane – all the present varieties have been developed through interspecific hybridisation Eg. Co1148, Co1158, co 541
- 21. Particulars Clone Pureline Inbred Mode of Pollination in the crops where they occur Cross pollination Self pollination Cross pollination Natural mode of reproduction Asexual (in most of the cases) Sexual Sexual Genetic make of plants in the natural population of such species Heterozygous Homozygous Heterozygous Obtained through Asexual reproduction from single plant Natural self pollination from single homozygous plant Artificial self pollination ( or other forms of inbreeding) and selection of several generation Comparision of clone, pureline, inbred
- 22. Particulars Clone Pureline Inbred Maintained through Asexual reproduction Natural self pollination Artificial self pollination or close inbreeding All the plants in the single entity are genotypically Identical Identical Almost identical Used directly as variety Yes Yes No (used in developing hybrids and synthetic varieties) Genetic make of plants within the entity Heterozygous Homozygous Almost homozygous Organisms where found Plants Plants Plants, Animals Comparision of clone, pureline, inbred
- 23. Bud mutation Bud mutation If the mutation occurs in the meristematic shoot in the early stages of bud development, all the cells of the bud will be mutant in nature, to the shoot developed from such bud will be a mutant one. This type of mutation will be called as bud sport. If a mutation occurs in the last stages of bud development, only some of the cells of the bud will be mutant in nature.
- 24. Chimera : A plant which has genetically distinct tissues lying adjacent to one another Chimeras classified into 3 types. 1. Periclinal chimera: Mutant and non- mutant tissues are in concentric layers one overlapping the other. They can be perpetuated by vegetative propagation. 2.Sectorial chimera: A segment of mutant tissue extending from the epidermis towards the centre. Mericlinal : It is incomplete periclinal chimera. The mutant tissues partly surrounds the other
- 25. Different types of chimeras
- 26. Tree Breeding & Clonal orchards Clonal orchards or seed orchard is an intensively- managed plantation of specifically arranged trees for the mass production of genetically improved seeds to create plants, or seeds for the establishment of new forests.
- 27. A seed orchard is often composed of grafts (vegetative copies) of selected genotypes, but seedling seed orchards also occur mainly to combine orchard with progeny testing. Seed orchards are the strong link between breeding programs and plantation establishment. They are designed and managed to produce seeds of superior genetic quality compared to those obtained from seed production areas, seed stands, or unimproved stands.