Distant hybridization - Copy.pptx

Bihar agricultural University sabour bhagalpur
813210 ,

1. Distant hybridization/ Wide hybridization Dr Anand Kumar Department of Plant Breeding and Genetics Bihar Agricultural University, Sabour (Bhagalpur )

2. Distant hybridization/ Wide hybridization Interspecific crosses: Crossing between two individuals of the two different species of the same genus. O. sativa x O. perennis Intergeneric hybridization: Crossing between two individual of the to different genera of the same family T. aestivum x Secale cereale (Triticale) Rimpu R. Sativus x B. oleracea ( Raphanobrassica ) Karpechenko-1928

3. Barrier to production of distant hybrids Failure of zygote formation : Zygote is not formed due to failure of fertilization. Fertilization often fails because Pollen tube is unable to reach the embro sac. Pollen tube may burst in the style of another species. e.g . Datura In some cases style is longer than pollen tube so the species with shorter style i.e. pollen tube is unable to reach the embryo sac.

4. 2. Failure of zygote development : Fertilization does takes place and zygote is formed but development of zygote is blocked at different stages due to different reasons. Lethal genes : Some species carry a lethal gene which causes death of zygote during embryonic n case of Aegilopes umbelullata (L1-early lehality , L2-late lethality, l- non-lethal. Genetic disharmony b/w two parental genome . Chromosomal elimination : Chromosomes are gradually eliminated from the zygote. This does not prevent embryo development but the resulting embryo and F1 plants are not true interspecific hybrid because they do not have true parental genome. The chromosome of one species is generally eliminated completely due to mitotic irregularities and in extreme case chromosome of only one genome may be present in the embryo which wwill be haploid. E.g. Wheat x Maize Incompatible cytoplasm : The cytoplasm of the female gamete may not be compatible with genome of the male gamete.

5. Endosperm abortion : When endosperm development is poor or it is completely blocked, it is known as endosperm abortion. Failure of hybrid seedling development: Some distant hybrids die during seedling development or even after initiation of flowering. In case of Melilotus in interspecific hybrid, chlorophyll deficient plants are fail to survive. Failure of hybrid seedlings may be because lethal gene, cytoplasm incompatability & genetic imbalance.

6. Techniques for production of distant hybrids Sufficiently large number of flowers are emasculated and pollinated. By determining the barrier to the production of hybrid embryo and then by using measures to overcome these barriers. e.g. part of style is cut off (maize) when it is crossed as female with Tripsacum . Maize x Tripsacum . Autopolyploidy also help in achieving interspecific hybrids. e.g. B. oleracea (2n=18) x B. campestris (2n=20). Tetraploid form produce embryo

7. Techniques for production of distant hybrids Species with same ploidy level, it is easier for hybridization. Species with different ploidy level are crossed hybridization b/w them are relatively difficult. In such cases 3 approaches may be useful: Species with higher ploidy level is generally used as female . Chromosome number of wild species should be doubled to overcome the sterility of the hybrid. e.g. wild spp. Of potato x S. tuberosum The chr . no. of F1 hybrid should be double to overcome the sterility of the hybrid.

8. Techniques for production of distant hybrids Use of Bridge species : Two spp. A and C are not crossed then third spp., B is taken. A. ventricosa (Resistance to eye spot disesase ) x T. aestivum does not produce hybrid. Third species T. turgidum first crossed easily with A. ventricosa and produced F1 then crossed with T. aestivum to produce hybrid which showed resistance against eye spot disease. Embryo culture

9. Reason for sterility in Wild crosses Cytogenetic basis of sterility - reduced pairing of chromosome - are of different spp. not homologous - most of the cases pairing not occur, we get univalent - Distribution of chromosome is not proper in cell division

10. Reason for sterility in Wild crosses Cytoplasmic sterility: In some interspecific hybrids cytoplasm may be the reason for produce sterility Reciprocal crosses produce fertile hybrids should be used A x B B x A

11. Segregation in Distant crosses Produces a very wide range of segregants and most of the segregants are weak and inferior to the parental species Most of the segregants have extremely new characteristics distinct from the two parental species Segregation pattern does not follow Mendelian ratio

12. Application of Wide hybridization Creation of new plant species is one of the major objective of distant hybridization. e.g. Triticale Production of Alien additition / alien substitution lines : Alien additition / alien substitution lines are produced in wheat, oat and tobacco . Alien addition line carries one chr . pair from a different species with in addition to the normal somatic chr . complement of the parent spp. These lines are produced to transfer disease resistance from wild species to the recipient species. But alien chr . Carries undesirable genes. Alien substitution line- has one chromosomal pair from a different spp. In place of the chr . pair of the recipient spp.

13. Application of Wide hybridization Disease Resistance: Late blight resistant gene has been transferred from its wild relatives Solanum demissum . Wider adaptability: Stability and earliness has been transferred from its wild relatives. Earliness has been transferred to cultivated spp. Of Brassica and Soybean from its wild relatives. Cold tolerance has been transferred in wheat, onion, tomato, potato, grape & rye. Wild relatives of wheat & pea contributes gene for drought & heat tolerance.

14. Application of Wide hybridization Improvement in Quality: Genes for increase protein content has been transferred in rice, soybean, oat and rye. Similarly, oil quality & oil palm has been improved by gene from its wild relatives. Mode of Reproduction : Apomixis - Genes for apomixis has been transferred in Maize and Tripsacum . Yield

15. Pre-breeding Pre-breeding is defined as all activities designed to identify desirable characteristics and/or genes from unadapted plant genetic resources(exotic and semi-exotic) that cannot be used directly in breeding populations and transfer them to an intermediate set of materials that plant breeder can manipulate to any kind of selection for crop improvement. According to the global crop diversity trust, pre-breeding is an art of identifying desired traits and incorporation of such traits into modern breeding materials ’. It is the interface of conservation of plant genetic resources (PGR) and plant breeding. It is a necessary step in the “linking genetic variability to utilization” use of diversity arising from wild relatives and other unimproved materials. Hence pre-breeding is referred as germplasm enhancement or germplasm conversion.

16. Aims of pre-breeding To reduce genetic uniformity in crops by using a wider gene pools of genetic material to increase yield, resistance to pests and diseases, and other quality traits. Broadening the genetic bases or genetic enhancement of raw materials which is achieved by identification of genes controlling traits of interest or transferring desired genes from unadapted to adapted background. Pre-breeding plays an important role in genetically improving the yield potential and other economically important traits such as abiotic and biotic stress tolerance/resistance in the germplasm. To developing early maturing genotypes fit well for multiple cropping systems.

17. Applications of pre-breeding in crop improvement Broadening the genetic base to reduce vulnerability

18. Pre-breeding using Wild Cajanus species and Pigeonpea cultivars for broadening the genetic base for pigeonpea improvement

19. Applications of pre-breeding in crop improvement Broadening the genetic base to reduce vulnerability Identifying traits in exotic materials and moving those genes into material more readily accessed by breeders Moving genes from wild species into breeding populations when this appears to be the most effective strategy and Identification and transfer of novel genes from unrelated species using genetic transformation techniques . The adoption of pre-breeding facilitates the efficiency and effectiveness of crop improvement programmes by enabling increased access to, and use of, genetic variations conserved in gene banks.