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Introduction to Maize Breeding

Nathan Schnur

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Overview

What is Plant Breeding?

Basic Genetics

Mendelian Genetics

Principles of Breeding Maize

Plant Breeding Methods

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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

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Basic Plant Genetics

DNA Primary carries of

heritable information

Composed of thousandsof genes

Genes Contain actual heritable

information

There can be manyversions of genes calledalleles

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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 asAa and called heterozygous.

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Basic Plant Genetics Cont

Alleles which are heterozygous

or homozygous affect the

phenotypes and genotypes ofplants

Phenotype

Visual appearance of the plant

Genotype

Genetic makeup of the plant

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Mendelian Genetics

Gregor Mendel

Famous geneticist from 1800s

His research consisted of selectivelybreeding garden peas

He developed two important laws of

genetics Law of Segregation

Law of Independent Assortment

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Mendelian Genetics Example

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Principles of Breeding Maize

Three Main Principles

Inbreeding

Hybridization

Heterosis

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Inbreeding

Main Goals

Increase the homozygosity at all or specific loci

in the plant genome Produce a plant which breeds true

Produce uniform plants

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Hybridization of Maize

Hybridization occurs when inbred parents aremated (cross pollinated)

Creates a heterozygous individual

Benefits

Increased heterosis (vigor) in F1 generation

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Heterosis (Hybrid Vigor)

Heterosis occurs when two homozygousindividuals are cross pollinated. This causes all loci to become heterozygous

The increased heterozygosity causesincreased plant vigor

Benefits of Increased Vigor Increased yield

Better standability

Better germination Overall better plant performance

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Maize Breeding Methods

Main Methods of Maize Breeding

Selfing (Inbreeding)

Sib Mating

Crossing

Test Crossing

Backcrossing

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Selfing

Selfing is the process ofpollinating a plant with itsown pollen

Benefits Increased homozygosity

Plants which breed true fromgeneration to generation

Decreased Segregation Disadvantages

Many generations of selfinglead to inbreeding depression

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Crossing and Test Crossing

Crossing is useful when trying tocreate 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 generalcombining ability of an individual

Ex. Inbred A is x to a tester which has adiverse selection of genotypes

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Backcrossing

Backcrossing is a methodwhich is used to improve atrait which a plant is deficient

in. Method

A hybrid plant which has thetrait of interest is crossed withone of its parents

The offspring are then crossedback to the parent, thusincreasing the frequency ofthe trait.

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Conclusion

Plant breeding is a complicated butbeneficial process.

There are many processes involvedwhich are used in the development ofnew varieties.

Remember if it wasnt for plantbreeding we wouldnt have such highyielding crops

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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

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Questions

Questions?