Transcript Principles of Plant Breeding

Introduction to Maize Breeding
Nathan Schnur
Overview





What is Plant Breeding?
Basic Genetics
Mendelian Genetics
Principles of Breeding Maize
Plant Breeding Methods
Plant Breeding

What is it?


Is the science and art of improving crop plants through the
study and application of genetics, agronomy, statistics, plant
pathology, entomology, and other related sciences.
Goals

Nutritional enhancement, yield improvement, environmental
stress tolerance, improved plant structure, or pest and
disease resistance
Basic Plant Genetics

DNA



Primary carries of
heritable information
Composed of thousands
of genes
Genes


Contain actual heritable
information
There can be many
versions of genes called
alleles
Basic Plant Genetics Cont’

There are two alleles for any gene




Dominant and Recessive
Two dominant alleles are denoted as
“AA” and called homozygous dominant
Two recessive alleles are denoted as
“aa” and called homozygous recessive
If one dominant and one recessive
allele is present then it is denoted as
“Aa” and called heterozygous.
Basic Plant Genetics Cont’


Alleles which are heterozygous
or homozygous affect the
phenotypes and genotypes of
plants
Phenotype


Visual appearance of the plant
Genotype

Genetic makeup of the plant
Mendelian Genetics

Gregor Mendel



Famous geneticist from 1800’s
His research consisted of selectively
breeding garden peas
He developed two important laws of
genetics


Law of Segregation
Law of Independent Assortment
Mendelian Genetics Example
Principles of Breeding Maize

Three Main Principles



Inbreeding
Hybridization
Heterosis
Inbreeding

Main Goals



Increase the homozygosity at all or specific loci
in the plant genome
Produce a plant which breeds true
Produce uniform plants
Hybridization of Maize



Hybridization occurs when inbred parents are
mated (cross pollinated)
Creates a heterozygous individual
Benefits
 Increased heterosis (vigor) in F1 generation
Heterosis (Hybrid Vigor)

Heterosis occurs when two homozygous
individuals are cross pollinated.



This causes all loci to become heterozygous
The increased heterozygosity causes
increased plant vigor
Benefits of Increased Vigor




Increased yield
Better standability
Better germination
Overall better plant performance
Maize Breeding Methods

Main Methods of Maize Breeding





Selfing (Inbreeding)
Sib Mating
Crossing
Test Crossing
Backcrossing
Selfing


Selfing is the process of
pollinating a plant with its
own pollen
Benefits




Increased homozygosity
Plants which breed true from
generation to generation
Decreased Segregation
Disadvantages

Many generations of selfing
lead to inbreeding depression
Crossing and Test Crossing

Crossing is useful when trying to
create hybrid seed.



Ex. By crossing “Inbred A x Inbred a” you
would obtain an F1 hybrid Aa
Crossing is used to produce the hybrid
seed farmers use to plant in the spring
Test Crossing is useful to test general
combining ability of an individual

Ex. Inbred A is x to a tester which has a
diverse selection of genotypes
Backcrossing


Backcrossing is a method
which is used to improve a
trait which a plant is deficient
in.
Method


A hybrid plant which has the
trait of interest is crossed with
one of its parents
The offspring are then crossed
back to the parent, thus
increasing the frequency of
the trait.
Conclusion



Plant breeding is a complicated but
beneficial process.
There are many processes involved
which are used in the development of
new varieties.
Remember if it wasn’t for plant
breeding we wouldn’t have such high
yielding crops
References

Fehr, W. Principles of Cultivar Development.
1993. Volume 1

Photos Courtesy of






www.pioneer.com
www.britannica.com
www.psu.edu
http://imbgl.cropsci.uiuc.edu
www.nsf.gov
www.scienceclarified.com
Questions
Questions?