1. Developing New Varieties: Plant Breeding
Source: USDA
Source: USDA
Source: USDA
Developing New Varieties: Plant Breeding
Source: USDA
Source: USDA
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. Plant Breeding Yield Quality Protection Private Sector, Universities,
Physiology
Statistics
Yield
Biochemistry
Molecular Biology
Genetics
Quality
Protection
Plant
Pathology
Nutrition
Entomology
Private Sector, Universities,
USDA, International Organizations

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

5. 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”
Source: USDA
Potato Germplasm
Introduction Station (NR6)
Source: USDA
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. Variation – Hybridization and Recombination
Parent 1  Parent 2 F1 F2
 (self pollinate)
Recombination
Hybridization

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 ( )

9. Selection
Figure courtesy of Larry Darrah

10. Selection Self-pollinated crops Cross-pollinated crops Backcross
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 Selection for Stalk Strength
This is a graphical depiction of the separation of the original population into 2 subpopulations over 6 cycles of selection. This is due to the selection for stronger and weaker stalks using the rind penetrometer and separation is apparent with very little crossover in stalk strength by 6 cycles. This selection has been continued out to cycle 12 where I began my research on this same population and analyzed several traits.
Cycle 0 and B73 x Mo Cycle 6 low and high

14. Divergent Selection Results
Figure courtesy of Larry Darrah
Divergent selection is selection of rind penetrometer resistance in two consecutive directions. Cycle 0 is the original population, and plants with high rind penetrometer resistance, meaning stronger stalks, are bulk pollinated with each other, and the same with low rind penetrometer resistance, meaning the weaker stalks, and the seeds become the plants of the next cycle. The numbers above the stalk cross sections indicate the amount of rind penetrometer resistance in pounds of force, and the change is noticeable with an increase in the high direction of selection and a decrease in the low direction. By the 6th cycle, you can see a change in the structure of the stalk. Cycle 6 high has a thicker rind, and a denser vascular system and pith. Cycle 6 low has a thinner rind and even a holey appearance to the pith.

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. 5-10 advance to the next generation
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

19. Cutting Back the Ear
Controlled Pollinations of Maize

20. Tassel Bagging
Controlled Pollinations of Maize

21. Corn Pollination
Controlled Pollinations of Maize

22. Soybean Anatomy

23. Soybean Anatomy

24. Soybean Anatomy
Stamen - ♂
Pistil - ♀

25. Soybean Pollination Photo courtesy of Duane Dailey

26. First Plant Breeders Thousands of years ago: Hundreds 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 vernalization Loss of dormancy/rapid germination Seed size and abundance Annual habit Loss 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. Does plant breeding work?
Corn Yield Trends: 1870 to Today
Bushels Per Acre
Year
Open Pollinated Varieties
Double Cross Hybrids
Single Cross Hybrids

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

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. Wheat variety ‘Ernie’
Photo courtesy of
Anne McKendry
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
Photo courtesy
of Anne McKendry

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

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. No rhizomes Rhizomes
Photo courtesy of Paul Beuselinck

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. Can We Continue Indefinitely?
Bushels Per Acre
Year

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