PLT 132 Plant Propagation Seeds part 2: Plant Breeding Principles D. W. Still

Transcription

1 PLT 132 Plant Propagation Seeds part 2: Plant Breeding Principles D. W. Still

2 Seeds Part 2 1. Virtually all agronomic and horticultural crops are produced by plant breeding. 2. Plant breeding defined: the application of techniques for exploiting the genetic potential of plants. 3. Domestication of plants and animals began about 13,000 ybp 4. Most plants and animals were domesticated thousands of years ago; very few have been domesticated today.

3 Malus sieversii Improving disease resistance of American domestic apples

4 Whole genome duplication Analysis of the apple genome suggests that a whole-genome duplication event in an ancestral genome, followed by loss of a single chromosome, led to the 17-chromosome karyotype of the cultivated apple. Expansion of particular gene families may have served as a reservoir for new gene functions, underlying the genetic basis of apple-specific traits.

5 Domesticated apple (Malus x domestica) originated in Central Asia

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8 Seeds Part 2 What traits can we breed for? - almost anything - qualitative traits PP, Pp pp

9 Seeds Part 2 What traits can we breed for? - quantitative traits Yield Skin color

10 Seeds Part 2 Terms: 1. Heterogeneous 2. Homogeneous 3. Homozygous 4. Heterozygous Heterogeneous mixed phenotypes / genotypes Homogeneous identical phenotypes / genotypes Homozygous Fixed alleles / genotypes Heterozygous mixed alleles / genotypes

11 Seeds Part 2 What traits can we breed for? However, it is not always clear how many genes control a trait

12 What were the targets of selection? 1. Assemble genetic materials 2. Obtain phenotype 3. Obtain genotype 4. Determine associations b/t 2 and 3 5. Identify quantitative trait loci (QTL)

13 Step 2: Obtain phenotype

14 Step 5: Determine associations between phenotype and genotype Association of SNP haplotype to skeletal size (chromosome 15) IGF1 SNP controls growth (insulin-like growth factor 1) common to all small breeds and nearly absent from giant breeds Sutter et al. 2007, Science

15 Step 5: Determine associations between phenotype and genotype Association of SNP haplotype to skeletal size (chromosome 15) Few genes, large effects Sutter et al. 2007, Science

16 Genetic consequences of domestication / breeding 1. Genetic bottlenecks 2. Founder effects 3. Genetic drift 4. Inbreeding depression 5. Loss of allelic diversity 6. Improved performance!

17 Seeds Part 2 1. Rice is a staple food for much of the world. 2. Two recent major changes: a) Increased harvest index b) heterosis by plant breeding 3. Challenges: a) Insect and disease pressure (~$1.5 billion loss) b) Fertilizer applications (~30% of N P use; ~10% arable land) c) Water shortage (Ag = 70% total water; rice = 70% of that) d) Quality e) Sustainability

18 Seeds Part 2 Modern breeding = Traditional breeding methods aided by molecular biology Fig. 1. Schematic representation of combinations of genes and approaches for the development of GSR Zhang, Qifa (2007) Proc. Natl. Acad. Sci. USA 104, Copyright 2007 by the National Academy of Sciences

19 Seeds Part 2 Fig. 2. Pest resistance of Minghui 63 individually harboring five different Bt genes Control Control Control Control Control Control Zhang, Qifa (2007) Proc. Natl. Acad. Sci. USA 104, Copyright 2007 by the National Academy of Sciences

20 Seeds Part 2 Breeding Systems A.) Self pollination Tomato Lettuce

21 Seeds Part 2 Breeding Systems B.) Cross pollination (outcrossing species) Sorghum Cactus Male whitish yellow; Female (male sterile red) photo Gary Odvody TAMU

22 Seeds Part 2 Terms: 6. Fixing of alleles 7. True-breeding 8. Effect of self pollination (Table 5-1) 9. Hybrid vigor = heterosis 10. Perfect flower

23 Effect of self-pollination (inbreeding) Within a population, the amount of heterozygous loci decreases by 50% each generation. Generation Self gen % homozygosity % heterozygosity Alleles become fixed F1 S F2 S F3 S F4 S F5 S F6 S F7 S F8 S F9 S

24 Seeds Part 2 Terms: 11. Perfect Flower 12. Monoecious (maize, cucurbits) 13. Dioecious (asparagus, pistacio) 14. Self incompatibility a) Sporophytic incompatibility b) Gametophytic incompatibility Perfect flower - Flower possessing both stamens and pistils Monoecious flower - Plant possessing both male and female flowers on the same plant Dioecious unisex flowers on different plants

25 Terms: 11. Perfect Flower 12. Monoecious (maize, cucurbits) 13. Dioecious (asparagus, pistacio) 14. Self incompatibility a) Sporophytic incompatibility b) Gametophytic incompatibility Seeds Part 2

26 Seeds Part 2 Pollen is distinct - the shape of each species is unique and chemically distinct Electron micrographs of pollen

27 Seeds Part 2 Mature pollen grains Determinants of compatibility are located on the outside layer, called exine

28 Mature pollen grain germination

29 Scanning electron micrograph of a pollinated stigma showing two interacting cell types, papillar cells (P) and pollen grains (Po). Nasrallah and Nasrallah, Plant Cell 5:

30 Gametophytic Self Incompatibility (GSI) Pollen is S1S3 or S3S4 Stigma/style is S1S2 The incompatibility of pollen is determined by the haploid (n) pollen genotype at the S locus. (rejection sites are on stigma and style) (Solonaceae, Rosacea, Fabaceae, Poaceae, Onagracea)

31 Sporophytic Self Incompatibility (SSI) Pollen is S1S3 or S3S4 S1 & S3 or S3 & S4 exine on pollen grains Stigma/style is S1S2 The incompatibility of pollen is determined by the dipoloid (2n) S genotype of the parent plant. (rejection sites are on papillar surface) (Brassicaceae, Asteraceae, Convolvulacea, Betulaceae, etc.)

32 Seeds Part 2 Terms: 15. Breeding line 16. Inbred line 17. Hybrid 18. Transgenic line 19. Landrace 20. Variety, cultivar 21. Specific epithet 22. Ecotype 23. Cline 24. Clone 25. Provenance Woody plant propagation 15. Breeding line maintained for use in a breeding program 16.Inbred line created by repeated selfing 17.Hybrid offspring from genetically distinct parents 18. Transgenic line developed from plants with recombinant DNA 19. Landrace primitive varieties (before breeding) 20. Variety lowest recognized taxonomic level (similar phenotypes) 21. Specific epithet Genus + species; e.g., Lactuca sativa 22. Ecotype population adapted to a geographic area 23. Cline continuous variation across geographic area 24. Clone genetically identical; vegetative, apomitic 25. Provenance climatic / geographic area from which seed originated

33 Examples

34 Plant breeding can be facilitated by using marker-assisted selection (MAS)

35 Marker assisted selection 1. Identify polymorphism between parents 2. Obtain genotype from parents and progeny 3. Obtain phenotype from parents and progeny 4. Establish association between genotype and phenotype 5. Future selections can be based on DNA-based markers

36 Confirmation of hybrids using polymorphic DNA markers P1 Polymorphic P2 F 2 F 2

37 Ecotypes, clines, and provenances 1. Adaptation to environment has a genetic basis. 2. Revegetation / reclamation work may require local sourcing of seeds for this reason. 3. Example: Echinacea angustifolia collected along a 1300 mile N-S climatic gradient. 4. Methods: Collect samples, extract DNA, compare DNA among populations, correlate to environmental variables (heat, cold, ppt) Photo by D.W. Still

38 Geographic & Climatic Cline Collection of Echinacea species along a 1500 km cline Still et al., 2006 Annals Bot

39 Geographic & Climatic Cline 1. ND 2. ND 3. SD 4. NE 5. NE 6. NE 7. KS 8. KS 9. OK 10. OK 11. LA CDD cooling degree days HDD heating degree days FFD freeze-free days Still et al., 2006 Annals Bot

40 Still et al., 2006 Annals Bot

41 Geographic & Climatic Cline results in genetic / phenotype cline ND/SD OK Still et al., 2006 Annals Bot

42 Seeds Part 2 Terms: Maintenance of genetic lines / seed trade 1. Genetic drift 2. Roguing 3. Selection by genotype or phenotype 4. Heritability 5. Genotype x environment interaction 6. Qualitative trait 7. Quantitative trait