Developing New Varieties: Plant Breeding

1. Source: USDA Source: USDA Source: USDA Source: USDA Source: USDA Developing New Varieties:Plant Breeding Sherry Flint-Garcia Research Geneticist USDA-ARS Department of Agronomy

2. Plants ~ 350,000 species world-wide < 300 used for food ~ 150 important in world commerce 15 major food sources wheat, corn, rice, barley, sorghum soybean, phaseolus (bean), peanut potato, sweet potato, cassava coconut, banana sugar cane, sugar beet

3. Yield Protection Quality Plant Breeding Physiology Private Sector, Universities, USDA, International Organizations Statistics Biochemistry Molecular Biology Genetics Plant Pathology Nutrition Entomology

4. Source: USDA Source: USDA Source: USDA Plant Breeding Identify/generate variation Germplasm collections Induced variation Hybridization/recombination Select for desired characteristics Depends on the crop and its end use Evaluate selections

5. Source: USDA Source: USDA Variation – Germplasm Collections Primary gene pool (same species) Elite cultivars Landraces (primitive cultivars) Wild plants of the same species Secondary gene pool Cultivars, landraces, or wild plants of different species “Wide crosses” Potato Germplasm Introduction Station (NR6) North Central Regional Plant Introduction Station (NC7)

6. Variation – Induced Variation Polyploidy Treat plants with chemical to induce polyploidy Mutation Natural rates are ~1 per million cell divisions Increase rate by using radiation or chemicals Biotechnology/Genetic Engineering Ability to cross the species/kingdom barriers

7. Parent 1 Parent 2 Hybridization F1  (self pollinate) Recombination F2 Variation – Hybridization and Recombination

8. Self- vs. Cross-pollinated Crops Self-pollinated – wheat and soybeans Uses pollen and egg from the same plant to produce seed Few seeds per hand pollination (3-15) Cross-pollinated – Corn and squash Uses pollen from one plant to fertilize an egg from another plant Many seeds per hand pollination (300-400)

9. Figure courtesy of Larry Darrah Selection

10. Selection Self-pollinated crops Mass selection – bulking of selections Pure line – test each selection separately Cross-pollinated crops Mass selection Half- and Full-sib selection – hybrids Recurrent selection – intermate selected lines Backcross Marker-assisted selection

11. Recurrent Selection Used for parent building/population development Generate families Test family performance Recombine selected families to complete a cycle of selection Cycle 0 random mate Cycle 1

12. Stalk Lodging – An Example of Recurrent Selection

13. Divergent Selectionfor Stalk Strength Cycle 0 and B73 x Mo17 Cycle 6 low and high

14. Figure courtesy of Larry Darrah Divergent Selection Results

15. Evaluation Phenotypic (trait) variation can be caused by: Environment = soil fertility, weather, biotic and abiotic stresses Genotype** = genes responsible for trait ** This is what plant breeders want to exploit Replicated trials to find stability across environments

16. Look at many – save a few! 300 Lines GOAL: Rapid Reliable Inexpensive 5-10 advance to the next generation

17. Corn Anatomy Tassel - ♂ Sheds pollen at maturity Ear - ♀ Each silk is attached to one ovule. Pollen tube grows down silk and fertilizes ovule. Photo courtesy of Maize Mapping Project

18. Shoot Bagging Controlled Pollinations of Maize http://www.maizegdb.org

19. Cutting Back the Ear Controlled Pollinations of Maize http://www.maizegdb.org

20. Tassel Bagging Controlled Pollinations of Maize http://www.maizegdb.org

21. Corn Pollination Controlled Pollinations of Maize http://www.maizegdb.org

22. Soybean Anatomy

23. Soybean Anatomy

24. Soybean Anatomy Stamen - ♂ Pistil - ♀

25. Photo courtesy of Duane Dailey Photo courtesy of Duane Dailey Soybean Pollination

26. First Plant Breeders Thousands of years ago: Likely women selected plants that they liked Hundreds of years ago: Farmers had their favorite “family” variety 1926 Pioneer Hi-Bred was founded First commercial hybrid seed company

27. First Traits Selected Non-shattering Altered photoperiod and vernalizationLoss of dormancy/rapid germinationSeed size and abundanceAnnual habitLoss of defensive structures Uniformity (germination and maturation)

28. Today’s Important Traits Altered Seed Composition Amino acid, fatty acid, starch Grain Quality: Baking quality, brewing quality Resistance to biotic and abiotic stresses Tolerance/resistance to diseases and insects Tolerance of poor soils – salinity, acidity Yield – the bottom line!

29. Bushels Per Acre Single Cross Hybrids Open Pollinated Varieties Double Cross Hybrids Year Does plant breeding work? Corn Yield Trends: 1870 to Today

30. Inbred A Inbred B  Bushels Per Acre Inbred A Inbred B Inbred C Inbred D   Hybrid 1  Hybrid 2 Single Cross Hybrid Year Double Cross Hybrid Heterosis in Maize

31. Green Revolution in Wheat Funded by the Rockefeller Foundation in 1940s and 1950s Led by Dr. Norman Borlaug Wheat pathologist and breeder Semi-dwarf varieties with resistance to stem rust Wheat yields in Mexico From 11 bu/a (1943) to 30 bu/a (1963)

32. Examples of New Varieties

33. Photo courtesy of Anne McKendry Photo courtesy of Anne McKendry Wheat variety ‘Ernie’ Derived from pedigree selection at the University of Missouri First soft red winter wheat with Scab resistance (fungal disease) Very early maturity that permits its use in double cropping systems

34. “Calrose 76” Semi-dwarf rice variety Developed in California in 1976 Product of mutation-breeding program Continues to be a parent in breeding programs today

35. Triticale: A “new” crop Triticale is a cross of wheat (♀) and rye (♂) followed by induced polyploidization High yield and baking quality Confers traits of tolerance to acid soils and salinity, drought tolerance, winter hardiness, rust and mildew resistance, and higher lysine Grown on 7.5 million acres (acid and marginal soils) in the world – primarily Australia, Brazil, France, Germany, Poland, and South Africa

36. Photo courtesy of Perry Gustafson Photo courtesy of Perry Gustafson Triticale on Acidic Soil

37. New Birdsfoot Trefoil with Rhizomes U.S. trefoil has persistence problems because of root and crown rot U.S. varieties lack rhizomes Paul Beuselinck, USDA-ARS, Columbia, collected a rhizomatous birdsfoot trefoil in Morocco and has bred it into U.S. germplasm resulting in release of ARS-2620 Grazing studies show increased persistence in pastures

38. Photo courtesy of Paul Beuselinck No rhizomes Rhizomes

39. Where Do Most New Varieties Come From? Selfing out of existing varieties and testing Crosses among existing lines and varieties followed by selfing and testing Yes, this approach seems to be self-limiting (funnel), but it has worked well thus far in many crops

40. Bushels Per Acre Year Can We Continue Indefinitely?

41. Glossary Phenotype: The observable physical or biochemical characteristics of an organism Genotype: The genetic constitution of an organism Inbred: A plant that is produced through self-pollination over many generations; “true breeding” Hybrid: A plant that is produced by cross-pollinating two inbreds Hybridization: The act of mixing different species or varieties of animals or plants Recombination: A combining of genes or characters different from what they were in the parents