Introduction to Maize Breeding

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? • 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 • 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 • www.pioneer.com • www.britannica.com • www.psu.edu • http://imbgl.cropsci.uiuc.edu • www.nsf.gov • www.scienceclarified.com

19. Questions Questions?