Untitled Flashcards Set
Plant domestication
Lecture 2
January 14, 2025
Domestication
Plants+Animals change away from wild status, its not beneficial for the organism but beneficial for US
If they were released back into the world, they would most likely not survive bc they are not adapted to nature but rather what we wanted to see in them
For domestication to work, these traits need to be heritable (genetic basis) and we need variation in the wild population (desirable traits) in order to select them (by humans)
Altered plant traits
2. Increase in seed size and number
Having more is pretty good
6. Increased palatability
In order to have more epeople eat it
1. Plants los their way to disperse seeds
3. Lost their dormancy
4. Shortened life cycle to annual instead of perennial
5. more compact growth habit
7. A bigger diversification
8. Domesticated plants are propagated through clonal
Plant fitness and seed dispersal
- reduction of seed dispersal
When seeds are ripe, they want to disperse these seeds away
Reduction of seed dispersal: a good thing fo farmers
Seeds are impossible to collect once they fall off the plant
Seed dispersal in the pov of a farmer is a bad thing
Reduction of dispersal
Grasses: corn, wheat, rice, barely, rye, spelt, millet, etc
Legumes: Soybean + all other beans, lentils, peas, chickpeas
Loss of seed dispersal in grasses?
Mechanisms and scientific evidence?
Spikelets are where seeds are made, disintegrate from stem, and they fall on the ground (called shattering) HUH!!??!?! Smooch edge when the spiklet falls off
Seed is located inside spikelet
Check slide 9
Shattering vs non-shattering: 2 genes control this
If they do not work. They remain in the raquis and the programmed cell death does not occur
Good for farmers: seeds don’t flal on the ground and aren’t lost
Early farmers slowly selected non-shattering genotypes
Ripe seeds have more nutrients, and farmers collected seeds from these yellow plants (didnt shatter)
Wild-type: ripe seeds more likely fallen off on the ground
Mutant plants: ripe seeds still on plant, no shattering
Seeds were kept from these, and some seeds were kept to sow and so the field next season kept most mutant seeds
THIS IS A HYPOTHESIS
Evidence.
Remnants of these spikelets were found
Fossil evidence at digs in Fertile crescent partial spikelets → edge visible
Wild-type: smooth edge as a result of predetermined cell death
Mutant: frayed rough edge
Stiff rachis → threshing necessary to get seeds
Threshing with animals, where cows are made to walk over these rachis to shatter it
Mechanical threshing is automatically done
Teosinte: wild ancestor of → Corn
They lay on top of the leaves bc the seeds have fallen off the rachiss
Corn we have now (domesticated), is non shattering
Beans
Wild type have seed pods that explode them out once ripe, or even split open to let seeds out
Domesticated seeds remain in the seed pod
Peas
That’s why we need to manually shell peas
Have the whole family to help
This is pre-mechanical
Increase in seed size
Occurred in barley + wheat(fertile crescent), rice (china), bean (india)
How did this occur?
Solution to increase in seed size: sowing into tilled soil
The procedure of breaking up the land (use of draft animals) and sowing the seeds into the open ridges
Seeds are sown into grooves and covered with soil
Larger seeds are more likely to emerge (more reserves), small seeds instead run out of food reserves before the start of photosynthesis
Over time, larger seeds make up majority of the gene pool
Increase in seed number
In wild barley, we have seeds inserted in two rows.
Cultivated barley, they are inserted in 6 rows, packing in many more seeds than wild
True for Teosinte to Corn as well, Teosinte is smalllllll
Dormancy, definition
State of quiet, inaction (“wait and monitor the environment”)
No growth, no germination
Wait for good environmental conditions
Bad conditions = frost and heat/drought
Scenarios without dormancy: no seedling protection
Winter-cold climates:
During summer, they finish flowering, late summer and fall they ripen seeds and disperse it. Without dormancy they are ready to germinate and grow in the fall that face our harsh winters and fs result in their death
Summer-dry climates (Mediterranean) (winter-wet)
Fall flowering, ripening of seeds in winter and dispersal, germinate in the spring, which would then face the harsh conditions in the summer which would kill it
Solution: Don’t germiante before harsh season, stay DORMANT
Dormancy in winter-cold climates: Wild plants
Seeds will only germinate after experiencing winter (aka in the spring)
They need at least 3 weeks of 0 to -4 C to germinate once spring comes = vernalization
Shorter period? -probably means the fall winter hasn’t occurred and they don't risk germination
Dormancy in summer-dry climates: wild plants
Seeds will only germinate once summer is over
The trigger is correct change of day length: photosensitivity!
Winter-spring-summer: day length increases
Summer-fall-winter: day length decreases
Seeds perceive day light and its relative durational change
Dormancy and the spread of crops into diff climates
Moving from Fertile Crescent to Spain (same climate of summer dry)
Most seeds he grabs germinate in the fall (well adapted for Fertile Crescent: wild type, photo sensitive)
Small proportion: mutants that just germinate whenever they get moist (no dormancy)
When sown in England, he does it in spring (best seasonal) choice but only harvests the neutral, bc spring is when days become longer, and so seeds that are photo-sensitive, do not germinate
They germinate during the fall which leads to a freezing death)
Photosensitive seeds die off
Domestication: Change of gene pool to photo-neutral seeds
Loss of photo-sensitivity needed in winter-cold climates
This bringing of wheat+barley to central europe, does not extend to chickpea and lentil
Chickpea, lentils have no loss of photosensitivity: no transfer into central europe
Loss of dormancy: a good thing for farmers!
Possibility to move to different types of climates
All sown seeds will germinate without needing to overcome any dormancy
Dormancy in domesticate plants: gone
Domesticated beans have also lost their ability for dormancyc
Same with rice
Wild: perennial → domesticated: annual
No need to remember names
There's no fruiting in year 1 for these perennial wilds plants, you need to wait for year 2
But for annual domesticated crop, they can be harvested in year 1
Wild and domesticated rice
What the fuck
Crossbreeding occurs between two species of rice, and this crossbreed is cultivated and there are the two msot common rice cultivars: O. indica, O. japonica
Wild → domesticated sunflower: ease of harvest
Many small flower heads to one/few large flower heads
The effect is only observes in not only sunflowers but also in maize, sorghum, pearl millet and others.
Made to be easier
Soy beans got more compact
Increased palatability: fewer toxins (2ary compounds)
Reduction in toxic or unpleasant compounds
A scale of how much defense a plant could have in comparison to yield
Wild → domesticated lima bean
Contains toxic cyanogenic glycoside in the domesticated lima bean
Domesticated have it much decreased or absent
Wild → domesticated nightshades (Solanaceae)
Wild: contains toxic alkaloids
Domesticated: much decreased or absent
Some still contain SOME toxic alkaloids
Which is an issue for some compromised, food-sensitive people
Wild → domesticated squash
Wild: contains toxic alkaloids, also very bitter
Domesticated: much decreased or absent
Flavour, texture, colour, cooking time, use, shelf life
Happened in apple and corn
Dent corn: grown for animals
Flint con: ??
Pop corn: water content inside, breaks open the shield
Flour corn: grinding up and making grits
Sweet corn: corn cobs or corn out of can
Waxy corn: has a diff type of starch used in
ALSO OCCURRS IN RICE
And potato
Russet; Bake and boiling
Red: steaming boiling
……..
Ingenious solution: flowers
Manipulation of environment to pick up and move pollen from one individual to another → outcrossing
Flowers have evolved to optimize inbreeding
BIOC37 Plants: life on edge (TALKS ABT BREEDING OF PLANTS)
But: outcrossing/random mating likely
Results in unwanted new genetic variation
Breaks sup desirable genetic lines (cultivars)
We would lose things we worked hard to put in these plants
Farmers want a fixation for selected traits: change reproductive system to selfing or NO sex
Early days of domestication
More desirable domesticated cultibar
Les sdesrable wild type
Random outcorss mating btween cultivar and wild type plants → desirable traits lost
Selfing is a lot more simpler and easier for us to keep the traits we want
Outcrossing ancestor → selfes domesticated cultivar
Chasmogamy (open flower pollination)
Cleistogamy (closed flower pollination)
Flowe rnever opens, mutation keeps the petals and staples closed, and so it rubs against its own pollen and they self
Fixation of good genotypes and traits
Open-pollinated flowers, but vegetative propagation
Farmers propagates crops asexually
While plant still produces seed, it will go for the clonal route an dpropagate through using the below ground organs
Slide 65
^^: Rhizomes
Could be surrounded by wild type bad traits, but since we dont use the seeds it doesnt matter!!!, as long as you go clonally, the composition of the seeds do not matter
Stolons (runners), grow on top of the soil, and then roots into the ground
U cut between the units, and they become independent to propagate and fixate good genotypes
Sugar cane, cut and nodes let sprout
Banana: stem cutting
Domesticated bananas are sterile even with seeds, the stem basis of a banana produces a branch that is cut which have eyes that let it regenerate
Put it into the ground to regenerate
Grapes (wine): grafting
So many branches, cut and more grown
FOR AVERY
Grafting also incredibly important in fruit trees
All of these fruit things can be grafted onto a substrate so you could have two diff types of branches on the same individual
Open-pollinated flowers, but vegetative propagation
Mostly thru rhizomes or stolons, rooting of branches or grafting