Back Cross Breeding Method

it is most important breeding method useful for transfer of dominant and recessive genes. helps to develop RILs and NILs

1. Handling of Segregation Population: Backcross Method Dr. Rajendragouda Patil Assistant professor Genetics and Plant Breeding School of Agricultural Sciences and Technology (SAST), NMIMS, MPTP Shirpur

2. Hybridization: crossing between genetically dissimilar plants. Intervarietal (two varieties or genotypes of same species) Interspecific (two species of the same genus) Intergeneric (two genera of the same family) Hybridization uses- 3 ways To combine several desirable traits in to single genotype To create vast genetic variability To develop hybrid varieties for commercial cultivation Methods to handle segregating population Pedigree breeding method Back cross breeding method Bulk breeding method

3. Back cross Back cross is the crossing of F1 with either of its parents is called as back cross Crossing F1 with its recessive parent is known as test cross Recurrent parent : the parent which is occurs repeatedly in the crossing Programme, it is superior in all traits except trait of interest Donor parent : the parent which used only once in the breeding Programme and Donets desirable genes, it is inferior to recurrent parent in all the traits except trait of interest Recipient parent : well adapted, high yielding variety, lacking one or two traits hence receives these lacking genes from other variety. Non recurrent parent: the donor parent,

4. Requirements Good recurrent parent Suitable good donor High expressivity of traits Character should be highly heritable Simple testing techniques Recovery of recurrent parent in minimum back crosses

5. Applications Applicable to cross and self pollinated crops Inter varietal transfer of simply inherited traits: (disease resistances and colour) Linkage drag : failure of transfer of simply inherited traits like disease resistance by B C method due to tight linkage between the gene being transferred and some other undesirable genes Inter varietal transfer of Quantitative traits: (earliness, Plant height, Seed size and shape, yield) Interspecific transfer of simply inherited traits: leaf and stem rust resistance from T. timopheevii , black arm from Gossypium species to G. hirsutum

6. Transfer of cytoplasm: (CMS and CGMS) T. timophoovii to T. aestivum Transgressive segregation: 1. the F1 may be back crossed to 1 ot 2 time to recurrent parents two or more recurrent parents may be used in BC method Production of isogenic lines: isogenic lines are identical in their genotypes, expect for one gene Germplasm conversions: conversion of photosensitive lines (using as recurrent parent) in to photo insensitive lines (donor parents )

7. Genetic bases of BC AA aa 1/4AA 1/4Aa 1/4aa 1/4Aa BC increases the frequency of desirable individual in population Aa F1 F2 1AA 2Aa 1aa Aa AA 1/2AA 1/2Aa Population gradually becomes identical to recurrent parent Normal Hybridization Back Cross Method   m = number of back crossing or selfing n = number of gene pair

8. The chance of breaking linkage drag (undesirable genes) is more with BC than selfing. Ex: ‘A’ is desirable gene and linked to undesirable gene ‘b’, desirable gene has to transferred from donor parent to well adapted variety. A a Bb A aBb F1 Adapted variety Desirable gene variety A and a have the tendency to inherit together to make it difficult to obtain AB combination. Since gene B is reintroduced with each back crosses. Probability of eliminating of b gene = P = recombination fraction m = number of backcross  

9. Transfer of Dominant traits RR rr R r F1 (50%) Stem resistance susceptible Non recurrent parent ‘B’ Recurrent parent ‘A’ R r rr rr Recurrent parent rr Recurrent parent R r rr rr Recurrent parent R r rr rr Recurrent parent BC 1 (75%) BC 2 (87.5%) BC 3 (93.75%) BC 4 (96.875%) BC 6 (99.218%) BC 5 (98.438%)

10. R r rr BC 6 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - BC 6 F 2 BC 6 F 3 Individual plant progenies in row Individual plant progenies in row Selection for resistant plant of recurrent patent Selection for Homogeneous progenies Replicated yield trials Seed multiplication and distribution to farmers Requires 11-12 years/seasons

11. Transfer of Recessive traits RR rr R r F1 (50%) Stem resistance Stem rust susceptible Non recurrent parent ‘B’ Recurrent parent ‘A’ R r RR RR Recurrent parent Recurrent parent Recurrent parent BC 1 BC 2 R r RR rr RR BC 1 F 2 R r R r RR rr RR BC 1 F 1 R r RR rr R r Recurrent parent RR BC 2 F 2 BC 3 F3 BC 3 BC 4

12. - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Individual plant progenies in row Replicated yield trials Seed multiplication and distribution to farmers Requires 11-12 years/seasons BC 5

13. Transfer of two or more traits into a single Recurrent parent Simultaneous transfer Stepwise transfer Simultaneous but separate transfer

14. Merits : New variety is nearly identical with that of recurrent variety except the gene of interest This is useful method to transfer oligogenes (disease resistance) and polygenes (oil and protein content) Extensively used for the development of varieties with multiple disease resistance; this method is used to develop NILs The male sterility and fertility restoration genes can be transferred through this method Interspecific gene transfer can achieved through this method only Variety developed by this method does not required multi-location testing ( bcz recurrent parent is already adopted) Demerits The newly developed variety cannot be superior to the recurrent parent except trait of interest Involve lot of crossing work, which is costly and time consuming Possibility of linkage drag

15. Achievements Cotton: 170-co-2, 134-co-2m, V797, Digvijay Wheat: Robin, K1, Blue bird, Tobari , HS-19 Bajra (Pearl millet): MS-521A, MS-541A, MS-570A

16. Multiline breeding Mixture of several purelines of similar height, flowering and maturity. It is mixture of isolines, closely related lines/genotypes and variety which is developed for commercial cultivation from any of these mixture is known as multiline variety. Isolines: refers to lines that are genetically similar except for the allele at one locus. The use of multiline cultivar was first suggested in oats by Jensen in 1952 Borlaug and Gibler in 1953 in wheat

17. Characteristics of good multiline It is applicable to self pollinated crops only (oat, wheat, soybean, groundnut) It is genetically divers because it is mixture of several purelines (homozygous and heterogeneous) More adaptable to environmental variations than pureline (more buffering capacity to changing env .) Very effective against multiracial disease. In relation to quality, generally less uniform and less attractive than that of pureline. yield is also comparatively less than pureline

18. Types of MULTILINES Mixture of isolines (developed by BC)-oats, soybean in USA Mixture of related lines (developed by crosses having one parent common) KSML-3 was released from Ludhiana- rust resistance Mixture of unrelated lines (developed by pedigree, bulk and SSD)

19. Development of multiline variety/ procedure

20. Achievement Oats , Soybean and Peanut in USA KSML 3 (8 multilines), MLKS 11 (8 multilines) , KML 7404(9 multilines) - Wheat for Punjab

21. Parameters Application Crossing Selection F2 to be evaluated Maintenance of record Effectiveness Testing Time taken Breeding procedure Adaption Use Features of new variety Pedigree SP and CP Only once Artificial Smaller than bulk Maintained Effective for oligo and poly genes Extensive 14-15 years Same for dominant and recessive Narrow Widely used Different from both parent Bulk SP Only once Both natural and artificial Larger than pedigree Not maintained Effective for oligo and poly gene Extensive Longer than pedigree Same for dominant and recessive Wider adoption Less popular Different from both parent Back cross SP, CP and Asexual Repeated Artificial Smaller Not maintained More effective for oligo and less for poly gene Not required Extensive 7-8 years Differs for dominant and recessive Like parent Widely used Identical with recurrent parents

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