LECTURE 35- plant breeding and biotechnology

what is plant breeding

The science of producing plants with desired traits through genetic modification

why does plant breeding exist

striving to make plants better due to environment changes, production tech, pest pressure, consumer preferences, and feeding more people

how is plant breeding performed

selection, hybridization, genetic manipulation

P = G + E

Phenotype = genotype + environment

VP = VG + VE

VP = phenotypic variance in a population

VG = variance from genotypic effects

VE = variance from environmental effects

low variance vs high variance

Low variance = difficult to select a certain trait

High variance = breeding for a desired trait is easier

what is backcross breeding

Used to add 1 characteristic to a crop

• Selecting the plants with desired traits in each generation and crossing them back with the original crop, to remove any other traits from the wild relative while keeping its desired traits

what is a simple gene

 individual either has a phenotype or doesn’t (purple vs white, or tolerant vs not tolerant)

• qualitative and discrete

what is a quantitative trait loci (QTL)

complex characters that must be measured 

(plant height or grain yield)

• Traits show a normal distribution due to multiple gene interactions + environmental effects

• QTL traits are continuous

what are challenged of plant breeding

self-pollinating/fertilising: inbreeding depression

outcrossing: phenotypes will be unpredictable

what is heterosis

Hybrids often show heterosis for all characteristics- will outdo parents in a specific trait

what is mutagenesis

 deliberate production of genetic variability through the use of various forms of energy or chemical treatment

• mutagenesis changes are randomized

Chemical mutagenesis: EMS (ethyl methyl sulfonate)

Irradiation: x-rays and gamma ray

EMS mutagenesis

EMS: induces point mutations through genome

• Single base paired changes throughout DNA

X-rays/gamma rays mutagenesis

induce chromosome breakages

what occurred during the green revolution

• Begun in 1945 by norman borlaug

• Awarded from developing high yield, disease resistant, semi-dwarf cereal crops (wheat, rice)

• Grain yield increases because less energy was put to vegetative growth

• Many countries became self-sufficient in grain production due to these results

green revolution critisicms

• Loss of native habitat 

• Increase in monocultures (single crop) with low genetic diversity- susceptible to pests and diseases

• Increased social inequality (money for companies)

• Questions of long-term sustainability

what are modern approaches to plant breeding

1. plant tissue culture

2. cell potency

3. auxin/cytokinin concentrations

4. genetic engineering

what is plant tissue culture

Generating new plants from plant tissue

• Growing plant tells, tissues, or whole plants on an artificial medium under controlled aseptic (sterile) conditions
  
  

Explants (the new plant tissue) form a callus: a mass of disorganised, undifferentiated plant cells

what is cell potency

A cell’s ability to differentiate into different cell types

Totipotent cells can divide to form any cell in an organism, and are capable of self-renewal

Pluripotent cells: can develop into different cell types, and capable of self renewal

Multipotent cell: can develop into different cells. Limited within a particular region/organ

what are auxin and cytokinin concentrations

Auxin + cytokinin levels can result in different tissues forming

More auxin than cytokinin = root formation

More cytokinin than auxin = shoot formation

Auxin and cytokinin levels equal = callus formation

what are the Requirements for tissue culture conditions

• Water

• Mineral nutrients (N, P, K)

• Vitamins and a carbon source (tissue will first be nonphotosynthetic)

• Plant hormones (auxin, cytokinin)

what are the applications of plant tissue culture

Mass production: plant should be clonal- clones of seedlings grow

Generating new variants (somatic hybrids): making new variants between plants that don’t naturally interbreed

Rapid screening of genetically modified organisms

Biopharming: using plants to produce compounds, often in biomedical industry

plant tissue culture step 1

Explant: fragment of tissue from plant as a starting point for culturing

plant tissue culture step 2

Explants cultured to generate more cells, so make a callus (solid medium), suspension culture or protoplast culture (liquid medium)

plant tissue culture step 3

Regenerating a whole plant from a callus through organogenesis or somatic embryogenesis

what is genetic engineering

genetically modified organism (GMO): any organism whose genetic material has been altered using genetic engineering

3 mechanisms:

• transgenesis

• cisgenesis

• genome editing

transgenesis

 genetic modification of a recipient line with genes from incompatible species with the recipient plant

• Done through the plasmid

cisgenesis (intragenesis)

genetic modified of recipient plant transformed with a natural gene for a crossable plant

• E.g closely related species or related species incorporated into recipient plant

genome editing

DNA is inserted, removed or replaced directly from a genome using molecular scissors to change a particular trait