Genes, Mendel and Meiosis
Why are Genetics Important? Key to plants being able to survive (evolve) changes in environment is genetic variation. Plant breeders use this genetic variation to breed new cultivars. This genetic variation is due to changes in the genetic code of a gene or the sequence that controls expression of the gene.
A gene is a DNA sequence coding for a single polypeptide, t-rna or r-rna
DNA RNA protein nucleic nucleic amino acids acids acids So changing the nucleic acid sequence of DNA can result in changing the amino acid sequence of a protein
Wild type Mutant Herbicide binding site Herbicide can t bind
Promoter region Gene Sequence Terminator region
AA x aa Aa AA Aa Aa aa
Law of segregation A pair of alleles for a given gene (trait) separate or segregate in the gametes equally. Law of independent assortment Allelic pairs of genes for two traits will behave independently of each other.
Genetic modification of crop plants. Increase productivity. Have better end-use quality. Can be produced with fewer input costs, with greater profit.
Self-pollinator Tolerant to inbreeding Few deleterious recessive alleles Closed flowers Little heterosis Out-pollinator Intolerant to inbreeding Many deleterious recessive alleles Open flowers. High heterosis
A-sexual Reproduction Reproduction through plant parts Reproduction through apomixis
Types of Cultivar Pure line. Out breeding populations. Clones. Hybrids.
Breeding Objectives Genetic Variation Selection
What factors are to consider in setting Breeding Objectives? People Politics Economics
Increase yield of product harvested over a specified area. Increase the inherent quality of the end product. Reduce the cost of producing the end product (while maintaining yield and quality).
Yield Increase yield of product per area. Increase the region of adaptation.
Increase harvestability
Improve Storability
Visual appearance Uniformity
Plant Breeding Operations Identify or create genetic variability Select for desirable recombinants
Artificial Hybridization
High Yield /Disease Susceptible x Low Yield /Disease Resistant High Yield & Disease Resistant
Wide Crossing Interspecific and Intergeneric Hybridization
Wheat 2n=6x=42 AABBDD or AABB Rye 2n=2x=14 RR Triticale 2n=6x=42 AABBDDRR or AABBRR
Induced Mutation
Alkylating agents: Most commonly used is Ethyl-methanesulphonate (EMS) Radiation: X-rays used to be most common source. Gamma rays, now most favors source.
Mutagens are indiscriminant agents. Clean up and stabilize mutants. Get rid of undesirable mutants. Selection of desirable mutants. Rapid screen necessary. In vitro screening.
[2x = 22] Colchcine [4x = 44] Autotetraploid
[2x = 22] x [4x = 44] [3x = 22] x Male Sterile [2x = 22] Seedless Watermelon
Plant Breeding Operations Identify or create genetic variability Select for desirable recombinants
Parents TT x tt F 1 Tt F 2 1:TT 2:Tt 1:tt 3 Tall : 1 Short
Parents TT x tt F 1 Tt F 2 Frequ n TT ¼ Tt ½ tt ¼
Parents TT x tt F 1 Tt F 2 Frequ n TT ¼ Tt ½ tt ¼ F 3 Frequ n TT ¼ TT 1/8 Tt ¼ tt 1/8 tt ¼ 3/8 TT 2/8 Tt 3/8 tt
Parents TT x tt F 1 Tt F 2 Frequ n TT X ¼ XTt ½ tt ¼
Parents TT x tt F 1 Tt F 2 Frequ n TT X ¼ XTt ½ tt ¼ F 3 Frequ n tt ¼ Genetically Fixed
Parents TT x tt F 1 F 2 Frequ n TT ¼ Tt Tt ½ Xtt ¼
Parents TT x tt F 1 Tt F 2 Frequ n TT ¼ Tt ½ Xtt ¼ F 3 Frequ n TT ¼ TT 1/8 Tt ¼ tt 1/8 3/6 TT 2/6 Tt 1/6 tt Segregation
Quantitative Genetics
Normal Distribution 1400 1200 1000 800 600 400 200 0 500 510 520 530 540 550 560 570 580 590 600 610 620
Genotype? Phenotype. Dominance (allelic interactions). Epistasis (non-allelic interactions). Environment.
A virus that parasitizes bacteria. Bacteriophase DNA passes into the bacteria cell and hence can replicate.
Produced by bacteria as a defense mechanism against phages. Enzymes act like scissors by cutting phage DNA at specific sites.
Molecular Markers P 1 P 2 P 1 P 2 F 2
If a particular trait is difficult to assess, then find an easily assessable trait that is closely linked to the difficult one.
Molecular Markers P 1 P 2 P 1 P 2 F 2 R S R S S R R R S R
Marker assisted selection. Difficult to evaluate characters. Quantitative Trait Loci (QTL s) DNA finger printing to identify genotypes (or cultivars). To secure proprietary ownership. Select parents with known genetic distance. Cytological information (mainly in interspecific hybrids). Saturated gene mapping.
Possible to transfer single genes from other species and non-plants into plant. Have transgenes expressed and to function successfully. Bypass natural barriers which limit sexual gene transfer. Allow breeders to utilize gene from completely unrelated species. Create new variability beyond that currently available in germplasm.
Find a desirable gene Develop a suitable construct Develop a mechanism to transfer the gene into the target plant Select cells that have been transformed Regenerate whole plants from single transformed cells Check functionality of tranformed plants
At present plant transformation is limited to transforming single genes. Techniques can only be applied to genes that have been identified and cloned. Identification of suitable promoters for the genes that are to be introduced. Transformation is still largely uncontrolled and many thousands of plants need to be screened to select ones with few deleterious effects.
Which pests and diseases affect crops Effect of plant pests and diseases Types of plant resistance Mechanism for pest and disease resistance Pest management systems.
Air borne fungi Soil borne fungi Bacteria Viruses Eelworms Insects Other, Incl Mammals
Reduce useable yield. All diseases and pests. Reduce end-use quality and storability. Most crops, especially fruits and vegetables.
Susceptible Host Pathogen No disease No No disease disease Disease Favorable environment No disease No disease No disease
Vertical resistance Controlled by a single gene. Results in distinct resistance classes. Resistance is usually absolute (yes or no).
Horizontal resistance. Controlled by multiple genes. Results in continuously variable levels of resistance. Usually resistance is not absolute.
Relationship between resistance genes and virulent genes is called Locks & Keys Locks (dominant resistance genes) can only be opened with the right keys (recessive virulent genes).
Plant Genotype Pest genotype Plant response aabb Any virulent gene Susceptible A_bb No virulent genes Resistant A_bb a a B B Susceptible A_B_ a a B B Resistant A_B_ a a b b Susceptible
Easy to manipulate genetically. Identification of resistant phenotypes is easier. Race specific. Advantages Disadvantages Resistance tends not to be durable for some disease types.
Advantages Horizontal resistance more durable than vertical resistance. Ability to control a wide spectrum of races. New pathotypes have difficulty overcoming all resistance loci.
Disadvantages Probability of combining all (or many) resistance alleles into a single genotype are low.
Resistance due to lack of infection. Hypersensitivity Mechanical
Resistance due to lack of spread after infection. Antibiosis: Plant resistance that reduces, survival, growth, development, or reproduction of pests feeding on the plant. Antixenosis: Plant resistance that reduces pest preference or acceptance of the plant.
Escape: Plant morphology avoids disease. Tolerance: Plant resistance that results in a plant suffering less injury or yield loss than a susceptible plant when both are equally infested.
Using genes from Bacillus thuringiensis (B.t.).
What is a weed?
Yield loss as they compete for: Interceptable light. Water. Nutrients. Harbor Pests: Over winter insects, host to diseases and cause infection. Reduce Crop quality Weed seed contamination.
Annual weeds: Complete life cycle in one year. Relatively easy to control. Seeds can remain dormant for many years. Biennial weeds: Germinant in the spring of one year, live vegetatively through winter and flower the following spring. Perennial weeds: Most difficult to control when established.
Mechanical: Non-selective herbicidal cultivation. Inter-row cultivation. Hand weeding. Cultural: Inter-cropping. Biological: Insects. Chemical.
Group 1 2 3 4 5,6&7 9 Description Foliar, monocots, ACCase (Acetyl CoA Carboxytase) inhibitors, binds to ACCase and disrupts fatty acid synthesis, which leads to membrane degeneration (i.e. Hoelon, Assure II). Foliar and soil, dicots, ALS (Acetolactate synthase) inhibitors, binds to ALS and disrupts synthesis of branched amino acids (i.e. Beyond). Soil applied, mainly dicots, Tubulin inhibitors, interferes with cell division (Treflan). Foliar, mainly dicots, synthetic auxins, upsets plant growth regulator balance by mimicking an increase of auxins (i.e. 2,4-D). Foliar and soil, mainly dicots, binds to a pigment in photosystem II and disrupts photosynthesis (Triazine, Sencor). Foliar, nonselective, EPES inhibitor, binds to EPES synthase and disrupts pathway, which is responsible for producing the precursors of aromatic amino acids (i.e. Roundup).
Wheat JGG Hydrid
Biological control: Encourage natural predators and parasites. Biopesticides. Cultural control: Resistant cultivars; trap crops; intercropping. Cultivation & tillage; crop rotation, timing. Mechanical & Physical control: Screens; traps. Reproductive & Genetic control: Introduce harmful pest genes; mass release of sterile insects. Chemical control: Pesticides used in an appropriate manner; hormones.
Next Class Test #3 Wednesday, November 18 th 2010 10:30-11:20