Propagation & Biotechnology
What is Vegetative Propagation?
Creating new plants from asexual means, or from non-reproductive tissues, like stems, buds, roots, and leaves
Cuttings
Soft tissues of stem, leaf and/or root are cut & allowed to produce adventitious roots
Not all plants root easily
Layering
Attempting to create adventitious roots while still attached to parent plant
Tip layering
Flexible stems buried under mound of soil to stimulate root growth.
When roots appear, the layered shoot is cut or removed proximal to the emerging roots.
Air layering
Bark is gashed to expose the vascular cambium to stimulate root growth, sometimes with rooting hormone
The wound is wrapped and protected until roots appear
The layered shoot is cut off the parent plant, below the roots, and then potted in growing medium
Dividing
Separating underground plant organs such as bulbs, rhizomes, stem tubers, etc.
A sharp knife or spade tool is used to split the underground plant organ
Root tubers can be challenging to propagate since they don't have axillary buds.
Grafting
Fusing woody tissues to get a hybrid plant with particular root attributes connected to desired shoot attributes
Inserting a cut stem (scion) unto a another stem with a root system (stock)
The vascular cambium of the scion fuses to vascular cambium of the stock
Plant Breeding
Hybridization
Crossing different varieties to get a more vigorous hybrid variety offspring (F1 generation)
In 1716, Thomas Fairchild created the first artificial hybrid plant (Dianthus caryophyllus x barbatus) from two different carnation species
Polyploidy
Plants that have more than 2 sets of chromosomes in their cells
These plants can sometimes be more vigorous
e.g. 3n = triploid; 4n = tetraploid
Autopolyploidy
Doubling of chromosomes within an individual
Non-disjunction during meiosis
Allopolyploidy
Cross between two close species
Offspring usually sterile, but…
…these taxa can still can spread asexually
…if autopolyploidy occurs in this “sterile” offspring then it becomes fertile and can produce gametes
Whole-genome duplications
Mutations
Changes in a plant’s chromosome or genes that change the morphology or physiology of the plant
Most are harmful, but occasionally beneficial mutations occur
Laboratory Techniques
Tissue Culturing
Plant cells grown on an artificial medium
Produce identical plants clones from a few plant cells or organs
New plants grown on medium with nutrients and hormones
e.g. Used to conserve endangered plant species
Mericloning
Growing and dividing the meristematic tissue of a plant on an artificial medium
First began in 1960s
Plants produced through this process are relatively identical
e.g. common with orchid breeders
Artificial Seeds
Formation of an embryo from the callus tissue of a desired plant, and placed inside a suitable matrix, which allows it to grow into complete plant.
In some horticultural crops, seed propagation is not successful
Benefits include long-term storage, easy handling in storage, and easy transport
Protoplast Fusion
Combining the organelles of two different cells
Combining crop and wild species for resistance
The removal of the cell walls of cells
The cells are then fused; hybrid cell forms its own cell wall
The cells are then grown into calluses, which then are further grown to plantlets, and finally to a full plant
e.g. Combining Solanum tuberosum & S. brevidens to create Leaf Roll resistant plant
Somaclonal Variants
Variants of cloned tissue cultures; some have superior characters
Chromosomal rearrangements are an important source of this variation
e.g. changes in chromosome numbers and structure, as well as DNA sequence and gene methylation
Some have superior characters such as resistance to disease & toxins
Sometimes undesirable results with unstable and random results
Transgenesis
Genes for a desirable trait are incorporated into bacteria to produce large amounts of recombinant DNA, which will be introduced to other plants.
e.g. Maize, Canola, Cotton, Soybeans, Sugar beet, Alfalfa
Commonly resistant to insects, or tolerant of glyphosate
Most transgenic crops are used for animal feed
What is Genetic Engineering?
What is genetic engineering? - from the University of Nebraska
Are genetically-modified plants "safe" to consume?
Meta-analysis of GM crop research (Research in 2014 PLOS One, summarized in Economist)
Impact of genetically engineered maize on agronomic, environmental and toxicological traits: a meta-analysis of 21 years of field data (Scientific Reports, Vol 8, Number: 3113, 2018)
Genetic Engineering Risk Atlas: a listing of all studies
GMO crops - Is there any peer-reviewed scientific evidence that questions their safety? Discussion on Research Gate
Questions for Thought
What is polyploidy, and how does it lead to plant diversity?
How can polyploidy occur from errors in mitosis?
How can polyploidy occur from errors in meiosis?
What are vegetative methods for propagating plants through non-sexual means?
How does your understanding of embryonic cells explain tissue culturing, mericloning, and artificial seeds?
What attributes of cell organelles might scientists want to select in protoplast fusion?
What is genetic engineering, and how is transgenesis a specific example of this?
Additional Reading
The American Chestnut Foundation Bails as GE Chestnut Develops Growth and Mortality Problems and Fails to Resist the Blight (Independent Science News 15Dec2023)
Artificial Life: Scientists create first-ever man-made chromosome (Brighter Side of News 9Nov2023)
‘Holy grail’ wheat gene discovery could feed our overheated world (The Guardian 7Jan2023)
That new chestnut? USDA plans to allow the release of GE trees into wild forests (The Hill 27Nov22)
Genetically modified corn does not damage non-target organisms (6Jun2022 ScienceDaily)
Creating a Better Leaf (The New Yorker, 6Dec2021)
What is a Genetically-Modified Crop? (New York Times, 2018)
Genomes Gone Wild from The Scientist: Weird and wonderful, plant DNA is challenging preconceptions about the evolution of life, including our own species.
Rewriting the Code of Life (The New Yorker, 2017)
Saving endangered plant species with genetic modification (Yale Environment 360, March 2018)
