Introduction lecture Flashcards
Genetic improvements in agriculture over time
The Distant Past
-Crop plant domestication
The Recent Past
- Hybrid seed
- The (First) Green Revolution
- Advances in breeding technologies
Now and Into The Future
- Breeding for improved human health
- Breeding for drought tolerance
- The Second Green Revolution
Plant domestication followed the end of the most recent glacial period: origin of agriculture
- Evidence suggests that people cultivated rye over 13,000 years ago, while continuing to hunt animals and gather wild plants in the Fertile Crescent- (now Iraq).
- This transition from hunting/gathering to agricultural lifestyles is a long, slow development process.
see: Allaby, R.G., Fuller, D.Q., and Brown, T.A. (2008) The genetic expectations of a protracted model for the origins of domesticated crops. Proc. Natl. Acad.
Sci. USA 105: 13982-13986, copyright National Academy of Sciences USA
Plants were domesticated in parallel in several regions
Plants were domesticated in parallel in several regions. See diagram from:
Reprinted by permission from Macmillan Publishers Ltd.: [Nature] Diamond, J. (2002). Evolution, consequences and future of plant and animal domestication. Nature 418: 700-707, copyright 2002.
Genetic modification arose as a consequence of cultivation
Natural variation occurs within a population
Planting seeds from “good” plants increased their representation in subsequent generations
See: University of California Museum of Paleontology, Understanding Evolution - www.evolution.berkeley.edu
During the domestication of maize cob size increased
The development of maize/corn may be the most remarkable plant breeding achievement in the history of agriculture
Teosinte, the wild relative of maize, has hard coverings over each grain.
Humans selected against these during maize domestication.
(see photos in lecture teosinte to modern maize)
The domestication syndrome: Maize as an example:
domestication of maize resulted in 5 key changes:
The difference between Teosinte and Maize is about 5 genes.
Domestication resulted in:
1: Increased grain size
2: Reduced branching
3: Tolerant of selfing
4: Non-shattering cobs
5: Starch, sugar, and oil-rich varieties
See: https://www.youtube.com/watch?v=mBuYUb_mFXA&ab_channel=biointeractive
Mauricio, R. (2001) Nature Rev. Gen. 2: 376
The domestication syndrome
Effect / Trait(s)
Better germination / Loss of dormancy, large seeds
Modified growth habit / Compact, determinate growth, reduced branching
Modified reproduction / Increased selfing or vegetative reproduction, altered photoperiod sensitivity
Greater seed harvest / Non-shattering, fewer and larger reproductive branches
Consumer appeal / Colour, flavour, texture, size, less toxins
Genetic modification through breeding leads to the development of new vegetables
See brassica olaraceae domestication diagram in lecture
Wild mustard domesticated to (with focus on):
- cabbage (terminal buds)
-brussel sprout (lateral buds)
-cauliflower (flower buds)
-brocolli (flowers and stem)
-kale (leaf)
-kohlrabi (root)
Crop domestication key facts
- ~ 250,000 plant species (but nobody knows the exact no. - there are probably many more)
- Over 80% of the world’s people rely on traditional plant-based medicine - Chinese medicine alone uses over 5,000 plant species
- Approximately 230 plant species from 180 genera and 64 families have been domesticated to some degree
- Of 30,000 edible plants, only 15 species supply 90% of our food – huge food security risk
- The most important families in terms of species and productivity are the Poaceae (grasses), Fabaceae (legumes), Brassicaceae (crucifers) and Solanaceae (potatoes/tomatoes)
- Wheat, corn, and rice > ½ calories people consume
- Most crops have been dispersed beyond their centres of origin e.g. soybean in the US, potatoes in Europe, coffee in south America now grown in areas far from their origins
Impacts of modern agriculture
- Current agricultural practices are good at maximizing yields
- New varieties of crops provide high yields and combinations of desirable traits
- Fertilizers provide faster plant growth and greater amounts of food produced per plant
- Pesticides are used to prevent losses to insects and provide the blemish less food
Resulting in neg effects:
Declining genetic diversity in food crops
Loss of wild varieties and varieties historically developed for that crop
yield focus resulting in loss of food crop and wild varieties reducing the gene pool for future breeding
Global land use
Large proportion of habitable land used for agriculture and most of this land is used for livestock – although the majority of calories are derived from plant foods – and also the majority of proteins!
https://ourworldindata.org/uploads/2020/01/Global-land-use-graphic-2048x1307.png
^ see diagram in notes
Environmental impacts of agriculture
A major draw of freshwater and of ocean/freshwater pollution due to chemical runoff
Agricultural livestock make up 94% of global mammals (excl. Humans) and 71% birds
https://ourworldindata.org/environmental-impacts-of-food
^ see diagram in notes
Agriculture is energy intensive
FAO tracked increase in oil usage and agricultural intensification correlation
^ see diagram in notes
Factors impacting global food production
Negative factors:
Environmental stress: Erosion, Salinisation, Chemical and biotic stresses
Climate change
Loss of arable land: Urbanisation and industrial development, Sea level rise – climate change
Positive factors:
Opportunities for improvement: Fertilisers, Irrigation, Biotechnology, Reduction of mismanagement
Gain of arable land: Utilisation of land reserves, Deforestation
(According to Springmann et al 2016 Global and regional health effects of future food production under climate change: a modelling study, The Lancet, Volume 387, Issue 10031, Pages 1937-1946)
Soil erosion and soil salinisation
Soil erosion a common issue in newly cleared land as tree roots no longer provide structural support.
Excessive irrigation can lead to higher salinity in water applied to fields resulting in increased salination.
Food supply has been diminished by bad weather in many crucial crop-growing
areas of the world
Agriculture and water
see figure from :
Gupta et al., Science 368, 266–269 (2020)
* Arrow shows increase in no. Of people living in areas of depleted water availability
* Increase in requirements for crops
Decrease in water availability
Food security definition from United Nations’ Committee on World Food Security:
“All people, at all times, have physical, social, and economic access to sufficient,
safe, and nutritious food that meets their food preferences and dietary needs for an
active and healthy life”
We are still in the process of answering the following questions:
- which crop species and varieties will grow reliably in each region?
- how much carbon plants can capture and store, and which species are best for this?
- how will plants be affected by the climate-induced migration of pests and diseases?
Advances in genetic technologies contribute to improved plants:
Examples of genetic technologies used in plant breeding:
*Marker assisted selection
*Smart Breeding
*QTL, Genome-wide association studies
*Recombinant DNA technology, gene editing and transgenic plants
