Lecture 5: Traditional crop breeding Flashcards
the varieties of plants we real on are of fundamental importance for
human survival
how are seeds stored around the world?
large seed banks
was domestication of plants achieved once?
NO, it was achieved a number of times across the world independently
how do we date when domestication has occurred? & e.g.
- Archeological records
- cucurburbita pepo peduncle 14C date of 7340 +/- 60 years BP
Characteristics of wild plant populations:
- species are genetically diverse
- within a local region, genes which confer a selective advantage will be predominant
- ECOTYPE
sub-population of wild plants which share local region, genes which confer a selective advantage reulsting in predominance is known as an
ECOTYPE
Characteristics of wild plant populations: a balance is set up between:
- adaptations to the local environment which tend to REDUCE local genetic diversity
- A requirement to respond to altering conditions which INCREASES genetic diversity
the traits we want in crops are often not those that have evolved naturally so humans
Selected traits
Traits selected for by humans for domesticated plants:
- High carbohydrate (or oil) - STAPLES
- Possess traits that are useful in an agricultural environment (seed retention, size etc)
- Therefore there were multiple domestication events occurred throughout human history
- creating a more reliable food supply
seed retention allows you to
harvest your crop all at the same time
Why were crops domesticated?
- MORE RELIABLE FOOD SUPPLY
- provides for a more predictable food supply
- -location
- -uniformity
- Gives greater yields since conditions can be controlled
- -irrigation
- -fertilisation
- -protection
- Select FOR beneficial traits, AGAINST undesirable traits, FOR new traits
What were the consequences of domestication of crops?
-yield increase
-population increases
-people stop moving , they live in settlement (villages, towns, cities)
-people have more time (science, art, communication)
Higher densities = more disease
-We want what others have = WAR
what do Cauliflower, Kale, Broccoli, Brussel sprouts, Kohl rabi, Cabbage have in common?
SAME SPECIES
-we’ve selected different traits
The agricultural environment is different to the wild environment, meaning the selection pressures are
also different
selection of a wild population in an agricultural environment generates
LANDRACES
continued selection from one individual plant will give rise to an
INBRED CULTIVAR.
Breeding introduces new genes into these cultivars
cultivation of potatoes was introduced to Europe in the
mid 16th century
potatoes originated in the tropical highlands of
South America
original varieties of potato compared to European varieties
ORIGINAL VARIETIES:
-diploid
-low yield
-flower when days are short (flowers in Autumn in Europe > no tubers)
-High alkaloid content (good for pest resistance but toxic)
EUROPEAN VARIETIES:
-tetraploid
-high yield
-flower when days are long(flowers in Summer in Europe)
-Low alkaloid content
-not toxic
Wild beet is:
leafy & is thought to be Beta maritima
Wild beet was domesticated in
prehistoric times
- leafy plants= swiss chard
- Root crop = beetroot
by 18th century sugar beet had been developed with
6% sucrose content
Beet & Napoleon & Achard
- in 1799 Achard developed a process for extraction sugar from sugar beet
- in 1811 Napoleon decreed that beet should be grown as an alternative to cane sugar (in response to British naval blockade)
sucrose content in beet over time:
- sucrose content rose steadily as a result of selection
- limit eventually reached
- genetic diversity exhausted
- physical max reached
- root sizes still increased further
where is sugar from today?!
still a division between cane (Tate & Lyle) and beet (British Sugar) manufacturers
illinois long-term selection experiment, maize tested for oil & protein content OUTLINE
-started in 1896
-163 ears of the maize variety Burr’s White (an open-pollinated variety) were tested for oil and protein content
-a subset of the grains were grown & re-selected every year
(• Illinois High Oil (IHO)
• Illinois Low Oil (ILO)
• Illinois High Protein (IHP)
• Illinois Low Protein (ILP))
-At various times the selection was changed e.g high protein varieties were selected for high oil etc.
illinois long-term selection experiment, maize tested for oil & protein content RESULTS - Protein
- Upper biological limit not attained, lower biological limit reached at certain level
- Can continue adding proteins but basic level required for cell to survive
illinois long-term selection experiment, maize tested for oil & protein content RESULTS - OIL
- lower biological limit reaches 0
- those which are switched, first selected for low then changed to high, never read high again as some genes are lost by selecting for low originally
potato eelworm:
- nematode pest
- major limitation to production in Europe in 1930’s
- 1200 different potato accession screened, 6 were found to be resistant
- -resistance due to the H1 gene
- -interferes with the reproductive lifecycle of pest. Eggs hatch but do not develop
- Nematode population also diverse, H1 gene only conferred resistance to sub-population
- other genes were found which gave resistance to other nematode races
How do we breed? (i.e. carrots)
commercial= good yield, good colour, susceptible
old = poor yield, poor colour, resistant
1) commercial variety & old variety CROSS
2) lots of outcomes in F1, repeated rounds of crossing and selection to achieve NEW commercial variety (good yield, colour + resistant)
hybrid vigour =
HETEROSIS
a hybrid between two genetically different parents which can give better yields than either parent.
-BECAUSE the plant is heterozygous
-an inbred line will be homozygous i.e. true breeding. Both copies of chromosome will be identical
crossing two different inbred lines gives rise to a
hybrid (F1)
hybrid vigour in Maize
- need to control pollination (to avoid self-pollination)
- plant male & females in alternating rows
- make females produce no pollen
- this was done using a natural mutation (but also made pants susceptible to Southern Corn Blight, unintended consequence)
- with maize u can also hand emasculate (cut the hassles off)
F1 hybrids in Maize hybrid vigour development:
- Naturally occurring male sterility allowed F1 hybrids to be generated on a commercial scale.
- The mutation which lead to sterility also lead to susceptibility to Southern Corn Blight.
- Crop losses were devastating.
modern agriculture uses monocultures of genetically uniform plants as the result in _ but ___
high yield but disease outbreaks can be devastating
IRRI was established in
1960 and released various rice lines
lodging in cereal =
more nitrogen results in elongation of stem which then collapse
____ genes resulted in the Green Revolution in agriculture
Dwarfing
The introduction of a dwarfing gene into rice reduced lodging problems:
• Yields of 11 tonnes/hectare with 150 kg N/hectare applied were achieved.
• The line was called IR8 and its cultivation spread rapidly.
• It is estimated that it replaced up to 5000 landraces and cultivars of rice in India alone.
-However, the IR8 line was susceptible to many pathogens and an intensive breeding programme followed.
• The IRRI collected 100,000 lines of rice for use in breeding programmes.
phonemics:
measuring the phenotype of a plant using automation
