1. Introduction to Maize Breeding
Nathan Schnur

2. Overview What is Plant Breeding? Basic Genetics Mendelian Genetics
Principles of Breeding Maize
Plant Breeding Methods

3. Plant Breeding What is it? Goals
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

4. Basic Plant Genetics DNA Genes
Primary carries of heritable information
Composed of thousands of genes
Genes
Contain actual heritable information
There can be many versions of genes called alleles

5. 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.

6. 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

7. 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

8. Mendelian Genetics Example

9. Principles of Breeding Maize
Three Main Principles
Inbreeding
Hybridization
Heterosis

10. Inbreeding
Main Goals
Increase the homozygosity at all or specific loci in the plant genome
Produce a plant which breeds true
Produce uniform plants

11. Hybridization of Maize
Hybridization occurs when inbred parents are mated (cross pollinated)
Creates a heterozygous individual
Benefits
Increased heterosis (vigor) in F1 generation

12. 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

13. Maize Breeding Methods
Main Methods of Maize Breeding
Selfing (Inbreeding)
Sib Mating
Crossing
Test Crossing
Backcrossing

14. 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

15. 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

16. 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.

17. 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

18. References Fehr, W. Principles of Cultivar Development. 1993. Volume 1
Photos Courtesy of

19. Questions
Questions?