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?