Transcript Effect of stalk strength, as measured by rind penetrometer

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
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
Plant Breeding
Physiology
Statistics
Yield
Biochemistry
Molecular Biology
Genetics
Quality
Nutrition
Protection
Entomology
Plant
Pathology
Private Sector, Universities,
USDA, International Organizations
Plant Breeding
Identify/generate variation
Source: USDA
Source: USDA
Germplasm collections
Induced variation
Hybridization/recombination
Select for desired characteristics
Depends on the crop and its end use
Evaluate selections
Source: USDA
Variation – Germplasm Collections
Primary gene pool (same species)
Secondary gene pool
Cultivars, landraces, or wild
plants of different species
“Wide crosses”
Source: USDA
Elite cultivars
Landraces (primitive cultivars)
Wild plants of the same species
Potato Germplasm
Introduction Station (NR6)
Source: USDA
North Central Regional Plant
Introduction Station (NC7)
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
Variation – Hybridization and
Recombination
Parent 1  Parent 2
Hybridization
F1
 (self pollinate)
F2
Recombination
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)
Selection
Figure courtesy of Larry Darrah
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
Recurrent Selection
Used for parent building/population
development
Cycle 0
Generate families
Test family performance
random mate
Recombine selected families
to complete a cycle of selection
Cycle 1
Stalk Lodging – An Example
of Recurrent Selection
Divergent Selection
for Stalk Strength
500
500
2446 data points for high
2508 data points for low
400
300
300
Cycle 0
200
Low sel.
200
B73 x Mo17
100
100
0
0
0
1
2
3
4
5
6
7
8
9
10
11
0
1
2
3
High mean = 6.54
400
Low mean = 3.09
2699 data points for B73 x Mo17
2530 data points for Cycle 0
Frequency
Frequency
Mean = 4.37 for B73 x Mo17
Mean = 4.40 for Cycle 0
4
5
6
7
High sel.
8
9
Rind penetrometer resistance bins (each 0.25 kg)
Rind penetrometer resistance bins (each 0.25 kg)
Cycle 0 and B73 x Mo17
Cycle 6 low and high
10
11
Divergent Selection Results
Figure courtesy of Larry Darrah
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
Look at many – save a few!
300 Lines
GOAL:
Rapid
Reliable
Inexpensive
5-10 advance to the next generation
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
Shoot Bagging
Controlled Pollinations of Maize
http://www.maizegdb.org
Cutting Back the Ear
Controlled Pollinations of Maize
http://www.maizegdb.org
Tassel Bagging
Controlled Pollinations of Maize
http://www.maizegdb.org
Corn Pollination
Controlled Pollinations of Maize
http://www.maizegdb.org
Soybean Anatomy
Soybean Anatomy
Soybean Anatomy
Stamen - ♂
Pistil - ♀
Soybean Pollination
Photo courtesy of Duane Dailey
Photo courtesy of Duane Dailey
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
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)
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!
Does plant breeding work?
Corn Yield Trends: 1870 to Today
160
Bushels Per Acre
140
120
100
80
60
Open Pollinated Varieties
Single Cross Hybrids
40
20
Double Cross Hybrids
0
1866 1876 1886 1896 1906 1916 1926 1936 1946 1956 1966 1976 1986 1996
Year
Bushels Per Acre
Heterosis in Maize
160
140
120
100
80
60
40
20
0
1866 1876 1886 1896 1906 1916 1926 1936 1946 1956 1966 1976 1986 1996
Year
Inbred
A

Inbred
Inbred
B
C
Hybrid
1


Inbred
D
Hybrid
2
Double Cross Hybrid
Inbred
A

Inbred
B
Single Cross
Hybrid
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)
Examples
of
New Varieties
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
Photo courtesy of
Anne McKendry
Photo courtesy
of Anne McKendry
“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
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
Triticale on Acidic Soil
Photo courtesy of Perry Gustafson
Photo courtesy of
Perry Gustafson
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
No rhizomes
Rhizomes
Photo courtesy of Paul Beuselinck
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 selflimiting (funnel), but it has worked well
thus far in many crops
Can We Continue Indefinitely?
160
Bushels Per Acre
140
120
100
80
60
40
20
0
1866 1876 1886 1896 1906 1916 1926 1936 1946 1956 1966 1976 1986 1996
Year
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