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Polyploidy breeding
- 2. Chromosome no.-3 types – haploid, diploid, basic number Haploid / gametic chr.no. (n) – half of somatic chromosome no. Diploid /zygotic chr. no.(2n)- Somatic chr.no. Basic no. (x) – gametic chr.no. of a true diploid species/minimum haploid chr.no of a species In regular diploids, 2n=2x
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- 6. Suitability of acrop for pp breeding depends on following factors: Crops which are not seed propagated(ie, vegetatively propagated crops where the economic part is not seeds) eg: forage crops, tubers, sugarcane, ornamentals Crops with low 2n no. Allogamy / cross pollination eg: Poaceae against Leguminosae
- 7. STEP 1 Artificialinduction and/or collection of naturally occuring pps and their maintanence. STEP 2 Detection of different kinds of pps. STEP 3 Isolation and handling of pps.
- 8. PP breeding includes: 1.Monoploid/Haploid breeding 2. Autoploid breeding 3. Allopolyploid/Amphi(di)ploid breeding 4. Aneuploid breeding
- 9. STEP 1 PRODUCTIONOF HAPLOIDS i. By induced parthenogenesis ◦ Using incompatible or irradiated pollen, haploids can be obtained by parthenogenesis. ii. Through wide crosses ( cross with distant species) ◦ eg: Hordeum vulgare х Elymus areanus Monoploid barley
- 10. iii. Through chromosomeelimination technique in distant crosses ◦ eg: Bulbosum technique H.vulgare х H.bulbosum (2n=2x=14) (2n=2x=14) Hybrid embryo Haploid barley (2n=x=7) (H.bulbosum chr. eliminated) eg: Solanum nigrum x S.luteum
- 11. iv. Cell culture/Tissueculture technique v. Anther culture technique by Guha and Maheswari ◦ Used in Datura, Nicotiana, Brassica, rice, wheat, triticale etc. ◦ Tanfeng is a haploidy derived rice variety developed in China(1976) vi. Through pollen culture ◦ Haploid pollen grains develop into haploid plants. ◦ Nicotiana – readily responding in anther & pollen culture. Technique to be followed varies depending on the species.
- 12. STEP 2 DETECTIONOF HAPLOIDS i. Detection through genetic markers ◦ Use of recessive & dominant genetic markers associated with seedling characters such as hypocotyl colour is useful in early detection of haploids. ◦ Eg : In potato, a dominant purple spot is present on haploid embryo-helps to distinguish at seed stage. ii. Through plant morphology ◦ Haploid plants are inferior to diploids – shorter, less longer leaves, reduced in breadth, stomata & guard cells – smaller in size.
- 13. STEP 3 DIPLOIDISATION Colchicine treatment – most effective & widely used method. Acts as inhibitor of spindle formation during mitosis & causes duplication of homologus chromosomes Colchicine is readily soluble in cold water, alcohol and chloroform but less soluble in hot water. Used as aqueous solution – relatively unstable. So the solution prepared fresh before each application. Affects only dividing cells-applied to actively dividing meristematic cells repeatedly at brief intervals.
- 14. Methods ofapplication: ◦ Seed treatment : Freshly prepared 0.2% solution applied for 1-10 days. ◦ Seedling treatment : At very young stage, seedlings are inverted and only the young shoots are dipped in colchicine solution & roots are protected;3-24hrs ◦ Application to growing apices : 0.1-1% solution applied to shoot apex using a dropper/cotton balls dipped in colchicine solution placed on shoot apices- repeated daily 0.5-1% colchicine +lemolin paste smeared on shoot apex-repeated 2-3 times per week. For woody plants, 1% colchicine with a wetting agent applied on shoot apices.
- 17. Includes triploidand tetraploid breeding I. TRIPLOID BREEDING • Produced by crossing tetraploid and diploid (4n x 2n) • Tetraploid as female – total qnty of seed low- proportion of 3n seeds high-produce vigorous hybrids • Diploid as female-total qnty high-proportion of 3n seeds low
- 18. • Triploids-pollen sterile-seedless-advantageousin watermelon • In common planting, diploid planted to provide pollen for satisfactory seed set in triploid in 5:1 ratio
- 20. Varieties Shonima& Swarna (2015) released from Kerala Agricultural University
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- 22. TV29 produceslarger shoots & biomass; yields more cured leaf per unit area and tolerant to drought than available diploid varieties
- 23. II. TETRAPLOID BREEDING Produced by chromosome doubling from diploid plants
- 24. Possible intobacco, Petunia etc. Autotetraploid maize has 43% more carotenoid content & vitamin A. Successful in forage crops, ornamentals etc. Pusa giant berseem -1st autotetraploid variety (Egyptian clover) released for large scale cultivation – higher green fodder yield Vetiver variety – Sugandha – 11% more oil yield
- 25. AMPHIDIPLOID –Allopolyploids diploid for all genomes present. STEP 1 Production of F1 hybrids by interspecific and intergeneric crosses STEP 2 Chromosome doubling by colchicine
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- 30. Developed byKarpechenko Chr.doubling
- 31. Combines yieldpotential and grain quality of wheat & disease and environmental tolerance (including soil conditions) of rye
- 32. World’s 1stinterspecific cotton hybrid (1972) Developed by Dr. B. H. Katarki from Cotton Research Station, Dharwad, UAS, Bangalore G. hirsutum х G. barbadense (Laxmi ) (SB 289 E) Varalaxmi
- 33. 2n=38 Hybridbetween Brassica campestris(syn. B.rapa) and Raphanus sativus (fodder raddish)
- 34. Irregular variationin chromosome no. By meiotic irregularities such as non-disjunction or lagging behind in metaphase plate result in n+1 & n-1 gametes. These gametes fertilized by normal gametes produce aneuploids. In desynaptic and asynaptic plants-a no.of univalents are seen in mid metaphase instead of bivalents which produce aneuploids Triploid plants produce aneuploid plants Tetrasomic plants produce aneuploid gametes resulting in aneuploid progeny.