The origins of agri cultura, cultivation of the fields Agriculture originated in various semi-tropical environments 10,000 years ago. Crop domestication is human-induced plant adaptation Centers of crop origin have wild relatives of the - PowerPoint PPT Presentation

Loading...

PPT – The origins of agri cultura, cultivation of the fields Agriculture originated in various semi-tropical environments 10,000 years ago. Crop domestication is human-induced plant adaptation Centers of crop origin have wild relatives of the PowerPoint presentation | free to download - id: 3b74c6-YTQ1M



Loading


The Adobe Flash plugin is needed to view this content

Get the plugin now

View by Category
About This Presentation
Title:

The origins of agri cultura, cultivation of the fields Agriculture originated in various semi-tropical environments 10,000 years ago. Crop domestication is human-induced plant adaptation Centers of crop origin have wild relatives of the

Description:

The origins of agri cultura, cultivation of the fields Agriculture originated in various semi-tropical environments 10,000 years ago. – PowerPoint PPT presentation

Number of Views:193
Avg rating:3.0/5.0

less

Write a Comment
User Comments (0)
Transcript and Presenter's Notes

Title: The origins of agri cultura, cultivation of the fields Agriculture originated in various semi-tropical environments 10,000 years ago. Crop domestication is human-induced plant adaptation Centers of crop origin have wild relatives of the


1
The origins of agri cultura, cultivation of the
fields Agriculture originated in various
semi-tropical environments 10,000 years
ago. Crop domestication is human-induced plant
adaptationCenters of crop origin have wild
relatives of the crop.Wheat evolved from three
wild grass speciesHybridization and polyploid
formation are important driving forces in crop
evolutionIn each center of origin numerous crops
were domesticatedGenetic diversity can be
measured at the molecular levelGenetic diversity
was lost as a result of domesticationLoss of
genetic diversity may allow disease epidemics
2
Where, how and why did agriculture begin?
Agriculture began in multiple places more or less
simultaneously some 8000 to 10000 years ago.
These are tropical or sub-tropical areas of
mid-elevation (3000 ft) with varied topographies
and a climate that has a distinct wet and dry
season (Mediterranean, Savanna or
Monsoon). Different species with similar uses
(cereal, legume, roots/tubers. fruit, fiber
crop, spices, stimulants) were domesticated in
each region. It is likely that climate change
induced hunter-gatherers to manage their food
sources more intensely and that primitive tools
(sickles) permitted greater food production,
setting in motion the first rise in the human
population.
3
Crop domestication is a selection process for the
adaptation of crops to the human environment
considering that humans are cultivators and
consumers
When humans harvest and re-plant they affect the
normal evolution of plants, selecting for
certain properties knowingly (seed color and
size) or unknowingly (germination time, rachis
strength). Domesticated plants spread from their
site of domestication to the region and then
farther out, displacing other, similar plants. In
wild individuals of the same species there is
much variability between individual plants many
properties such as plant height,seed size,
disease resistance,stress tolerance, yield per
plant, etc. This variability, which has a genetic
basis, is lost as the emerging crop gradually
replaces the wild plants. Continuous
back-crossing makes this a slow process.
Reproductive isolation accelerates it.
Barley mutant with non-brittle rachis (left) and
wt (right)
4
Plant characteristics that were selected for
during domestication.
Reduction/loss of the means of seed dispersal
Brittle rachis
Shattering of pods Reduction/loss of dormancy
(rapid germination after sowing) More compact
growth habit (no vines) Shorter time to
flowering and maturity Gigantism (big seeds,
fruits) Photoperiod insensitivity
Reduction/loss of toxic compounds
5
Where did our crops originate?In 1882, Alphonse
de Candolle, a French systematic botanist
(taxonomist) proposed that the crops of the world
originated in 3 centers Mesoamerica, the Fertile
Crescent of the Middle East, and South East Asia.
He based his proposal on the presence of wild
relatives of the major crops (rice, wheat, beans)
that look like the crops and on archeological
evidence.
6
Evidence for the origins of agriculture comes
from archaeological excavations and botanical
observations on the distribution of the relatives
of our domesticated crops
Nikolai Vavilov, a Russian geneticist, was a
tireless plant prospector and collector. He
postulated that the region of greatest diversity
of the wild relatives of a crop plant is also
its center of origin. He proposed 8 centers
of origin. Further research by Jack Harlan in the
USA modified this to 3 real centers and 3
non-centers.
Vavilovs map
Harlans map
7
The origin of bread wheat.
The wild relatives of bread wheat, Triticum
aestivum, still grow in the Middle East
The Fertile Crescent
Mesopotamia
8
The Fertile Crescent
Einkorn
Aegilops
Goat grass
9
When an A gamete from the AA plant fuses with a B
gamete from the BB plant, this fusion product
normally produces a sterile AB plant, because the
chromosomes cannot pair during meiosis when the
AB plant would produce gametes. However, if early
on there is a duplication of the chromosomes to
AABB, then this plant can form AB gametes and a
new species has arisen.
Chromosome doubling
Chromosome doubling
10
The domestication of wheat involved a migration
out of the area of origin. The hybridization of
Einkorn (AA) and Aegilops (BB) occurred in the
Fertile Crescent. The second hybridization with
Triticum tauschii (DD) occurred south of the
Caspian Sea.Each time there had to be a doubling
of the chromosome number.
Doubling of the chromosome number
(polyploidization) is a rare event. Because
wheat can continue to grow vegetatively with
tillers (side shoots) for several years, this
makes it more likely that such an event will
occur. Then that particular shoot will have seeds.
Varieties of wheat and barley that were found at
archeological sites with evidence that they were
exploited as food sources in the Near East.
Wheat with tillers
11
How do we know that wheat evolved this
way?Cytogenetics is the study of chromosomes
their structure (what they look like after
staining) and where certain genes are located
(gene mapping). This branch of science came
before genome sequencing
Aegilops speltoides B genome
Einkorn, A genome
12
The spread of agriculture and domesticated wheat
eastward in the Mediterranean and then the rest
of Europe and westward in Asia (to India)
occurred at a rate of about 500 km per 1000
years. 8 founder crops were associated with the
emergence of agriculture in the Fertile Crescent
8000 years ago. Crops traveled with their
associated weeds and the weeds became crops as
they reached other climatic zones where they were
better adapted (rye, for example). The entire
agricultural system moved (wheat other crops
domesticated animals)
13
A number of plants (corn, beans, peppers) were
domesticated in the cool tropical highlands of
Mexico.Many species of teosinte - the progenitor
of modern corn - grow wild in Mexico, often in
close proximity to corn fields (see below).
Teosinte is a wild grass with nutritious seeds
but seeds that readily disperse (brittle rachis)
and are encased in a hard fruit (casing).
Ear of teosinte
14
The origin of corn (Zea mays)Modern maize has
genes from two different species of teosinte
(parviglumis and mexicana)
Corn evolved from small forms (lt 2 cm, 4 rows) to
larger, multi-row forms (gt 13 cm, gt8 rows) by
A.D. 1500
15
All cultures domesticated cereals and legumes,
which are agriculturally and nutritionally
complementary
Latin America Corn and common bean China Rice
and soybean Middle East Wheat and lentil Africa
Sorghum, rice, cowpea and groundnut Human
Nutrition Legumes, except soybeans are low in
the sulfur amino acids cysteine and methionine.
Cereals are low in lysine and tryptophan. Eaten
together the two provide a complete
protein Agronomy Legumes fix nitrogen in a
symbiosis with bacteria that Live in root
nodules. Cereals respond to nitrogen
fertilization with improved yields
16
Land racesRelative reproductive isolation and
differing conditions of soil, nutrients,
diseases, insects, water, day length etc created
numerous landraces of our crops. However,
subsistence farmers are always trading seeds, so
land races are not static entities, but their
genetic make-up changes. All land races of one
species have the same genes (unless deletions
occurred), but many different alleles
Corn from different fields
17
Collecting a peanut landrace In Amazonia
An example of 700 collection sites of wheat land
races to test them for drought and salt
tolerance. All these land races originally came
from the Fertile Crescent as wheat spread out
East and West, some 8000 years ago.
Harvesting a wheat land race In Pakistan.
18
Loss of genetic diversity as a result of
domestication and selection
Wild species
Early domesticates
Modern varieties
Figure 1
19
Domestication resulted in the loss of
biodiversity. Subsequently plant breeding reduced
it even more.
  • An infinite number of different individuals.
    Domestication
  • occurred in only a small portion of the
    entire area where the
  • wild relatives were found.
  • 2. 1000 to 10000 landraces grown by farmers as
    the crop spread
  • 3. 10 to 50 varieties produced by plant breeders.
    Although plant
  • breeders constantly produce new varieties,
    the new ones replace
  • the old ones.

20
The loss of alleles in a genetic bottleneck
caused by using a small sample to proceed to the
next generation. During crop domestication there
were 2 types of sample reductions the crop was
domesticated starting with wild relatives in a
restricted area and, each year a sample that may
not have contained all alleles was saved for
planting.
21
Molecular genetic diversity of wild relatives and
cultivated crops using chloroplast DNA sequences.
22
In the course of crop evolution there occurred
two major bottlenecks in the loss of
biodiversity between the wild progenitors and
the landraces and again between the landraces
and the modern cultivars The example below if for
the common bean (Phaseolus vulgaris).. There
are 12000 cultivated varieties (landraces) of
common bean!
23
Genetic uniformity (lack or diversity) has major
advantages, but also drawbacks.
An epidemic of southern corn leaf blight
(Bipolaris maydis) swept through the Southern US
in 1970, decreasing the national harvest by 15 .
A new race (variant) called race T infected all
corn varieties carrying a particular gene. This
gene was present in a very high of all hybrid
corn varieties sold to farmers.
An epidemic of late leaf blight of (Phytophtora
infestans) of potato wiped out potato crops in
Europe in 1845-1846 contributing to the Irish
famine and mi- gration to the US.
24
Hybridization and polyploidization of weeds
produced crops!
Rapeseed/canola
25
Just a few mutations produced these different
crops from one ancestor of Brassica oleracea.
26
(No Transcript)
About PowerShow.com