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Developing New Varieties: Plant Breeding

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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

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