Topic 1 Food Security and Safety Flashcards
(130 cards)
1
Q
What is food insecurity?
A
food insecurity. This means they cannot access the food they need in either the correct quantity or of a suitable quality that is conducive to a healthy life
2
Q
Currently, we produce enough to feed the world’s population (around 7.2 billion in 2015), that is to supply every person on Earth with an adequate 2800 calories per day and 75 g protein. But despite this we still have a world population with approximately 870 million malnourished people (World Hunger Education Trust, 2015) and a stunning 2.8 billion overweight people (World Health Organization, 2015).
Bearing this in mind, why do we currently struggle to adequately feed our population? Click on the ‘Edit’ button below and use the response box that appears to type and save your answer.
A
There are serious problems with global food systems which mean that food supplies are not equitably distributed. Issues affecting global food security are extremely complex; they depend not just on global farming practices and the agricultural sciences that support them, but on political and social issues too.
3
Q
What is the world population?
A
7.7 billion (2019)
4
Q
As with all the topics in this module, it’s important that you keep in mind both the social and scientific aspects of the topic. So as you read this material, it’s worth bearing in mind what three questions:
A
To what extent do science and technology offer solutions?
To what extent can scientific methods and thinking contribute towards informed debate?
Are there aspects of the topic where an understanding of the scientific issues alone is insufficient to offer meaningful solutions?
5
Q
It is possible that some of the reasons for reduced food security and poor nutrition given in the table may be addressed by the application of science and technology or at least by taking a science-informed approach.
Can you suggest ways in which science has already offered solutions to some of the world’s food security issues? Click on the ‘Edit’ button below and use the response box that appears to type and save your answer.
A
You may find it useful to compare your list with the following one suggested by the author.
An understanding of plant genetics has already contributed to the breeding of more productive plants, which are well suited to changing environmental conditions. Further developments in this area are well established.
An understanding of environmental sciences has contributed to a better understanding of the requirements of plant growth and how these can be optimally supplied.
Analytical science has improved food safety testing, ensuring our food is safe to eat.
Scientific studies in the field known as dietetics have established the general requirements for a healthy diet, the need for specific nutrients and how food can be fortified to contain these nutrients.
The chemical sciences have informed agricultural techniques that allow greater productivity, including use of fertilisers, pesticides and herbicides.
6
Q
what should be considered in the four module themes as you study each individual topic?
A
Communication
Risk
Ethical issues
Decision-making.
7
Q
What huge changes in agricultural practice has come about in the last 20 years?
A
This increase has largely come about as a result of the application of frequently criticised ‘modern farming’ techniques. On a simple level, this means higher-yielding crop plants, larger farms, more efficient (mechanised) equipment and use of fertilisers, pesticides and irrigation. Application of these techniques has already boosted food production significantly.
8
Q
What is the ‘green revolution’?
A
In the 1950s there were real fears that global food provision was insufficient to meet the demands of the growing population and that widespread famine was imminent in India, in East Pakistan (which since 1971 is largely Bangladesh) and also in South-East Asia. The previous 20 years had already seen huge changes in agricultural practices in the wealthier countries that had allowed food production to increase very significantly.
This increase has largely come about as a result of the application of frequently criticised ‘modern farming’ techniques. On a simple level, this means higher-yielding crop plants, larger farms, more efficient (mechanised) equipment and use of fertilisers, pesticides and irrigation. Application of these techniques has already boosted food production significantly.
In the face of concerns about food security, these agricultural practices were exported to the world’s low-income countries, beginning the so-called ‘Green Revolution’.
9
Q
How many crop plants make up 90% of the worlds food energy intake?`
A
15 crop plants provide 90% of the world’s food energy intake.
10
Q
What 3 crop plants make up 60% of the worlds energy intake?
A
Rice, maize (corn) and wheat are the most significant of these crop plants, providing 60% of the world’s food energy intake and are the staple food for 4 billion people (Food and Agriculture Organization of the United Nations, 1995).
11
Q
How many edible plants in the world is there estimated to be?
A
There are estimated to be 50 000 edible plants in the world
12
Q
Suggest a reason why the value for maize production is misleading when considering its impact on food security.
A
Not all crops are grown for food. You may be aware that around 20% of the world’s maize production is for other uses including biofuel.
13
Q
What are genetics?
A
Genetics is the study of the patterns of inheritance of characters from one generation to the next.
14
Q
Explain what a F1 hybrid plant is?
A
The first of these developments, in the 1930s, was the widespread introduction of ‘F1 hybrid plants’. Plant scientists discovered that they could produce superior varieties of some staple crop plants by selecting plants of the same species with different advantageous characteristics and crossing them together. The aim is to produce offspring that show the advantageous characteristics of both parents. The underlying techniques of plant breeding rely on an understanding of the science of genetics.
15
Q
What is a gene?
A
Genetics is the study of the patterns of inheritance of characters from one generation to the next. These heritable characters are known as genes
16
Q
What is a genotype?
A
heritable characters are known as genes and it is possession of different genes within an individual organism’s genotype that maintains differences (known as biological variation) between members of the same species.
17
Q
What is a phenotype?
A
Some of these heritable characters in plant genotypes confer advantageous characteristics on the plant; as a result, these individuals have favourable phenotypes given certain environmental conditions.
18
Q
What is the difference between phenotype and genotype and what is the relationship between the two for any given individual?
A
The phenotype describes the sum of all the characters an individual organism possesses; these can be structural, biochemical, behavioural or physiological features. The full complement of genes possessed by an individual, is its genotype. The phenotype of the individual is the combined action of their genes (their genotype) and their environment.
19
Q
Suggest some potentially desirable phenotypic characteristics for crop plants that plant breeders might be interested in breeding into their crops.
A
You may have included any or all of the following phenotypic characteristics in your answer and you may have thought of additional characteristics not included here:
drought/flood resistance heat or cold tolerance resistance to disease resistance to insects specific flavour seed shape or size rapid maturation time ease of processing (e.g. grain is easily separated from the crop plant).
20
Q
What are the two main stages of producing F1 hybrids?
A
Repeated inbreeding by self-fertilisation of the two selected parental varieties of crop plant
followed by
Cross-breeding of the two parents together to ensure cross-fertilisation.
21
Q
What does self-fertilisation mean?
A
As each plant produces both male and female gametes, it is possible for many species to produce seeds by fertilising themselves. To do this the plant’s own pollen (male gametes) is used to fertilise its own ovules (female gametes).
22
Q
What is repeated inbreeding?
A
Repeated inbreeding (self-fertilisation) Plant breeders select two parental varieties of the crop plant of interest with different advantageous phenotypes. For example, they may choose a cold-tolerant variety and a high-yielding variety of the same species. They then allow these parental varieties to self-fertilise repeatedly for many generations until they are sure that the plants ‘breed true’ for the given characteristics.
23
Q
What is the desired effect of generations of self-fertilisation?
A
The desired effect of the generations of self-fertilisation is to check that the plants consistently produce offspring that are just like themselves, i.e. true breeding. This means there are no ‘hidden’ recessive genes in the parental genotypes, which may ‘reappear’ in the progeny of the all-important cross-breeding step
24
Q
How many generations of self fertilisation need to be done to make sure plants are breeding true?
A
It takes around ten generations of self-fertilisation to be sure that the plants are breeding true.
25
Genetically describe what will happen to both alleles after generations of self fertilisation? and what is this called?
Technically this means that the parental plants are likely to be homozygous for most of their characteristics; that is, both the alleles (alternate forms of the same gene) for any characteristic are the same.
26
In genetics what do the terms allele, dominant and recessive mean?
The alternate forms of genes are referred to as alleles. A dominant allele is one that is expressed or shows up in the phenotype even when a recessive allele for the same gene is present in the genotype. The allele which is not expressed is said to be recessive.
27
What does F1 mean?
first filial generation
28
What is cross breeding?
After self fertilising (10 generations) to get the desired genetype. The next step is to cross these two true-breeding varieties of plants together by removing pollen from one parent and adding it to the female flowers of the other selected parent. The pollen fertilises the ovules, which develop into seeds. Once the seeds are grown into mature plants, it is possible to tell whether this generation of plants have inherited the desired advantageous characteristics from both parents. This new generation of plants are referred to as F1 hybrids. F1 means they are a first filial generation.
29
What does hybrid mean?
Hybrid means they are the product of two different parental varieties
30
What is the result of hybrid plants after cross breeding?
These resulting hybrid plants are said to have hybrid vigour or heterosis; they tend to be more robust, uniform in size and maturation time, but also show, to an even greater extent, all the favourable characteristics of the parent plants. Many different varieties of F1 plants were bred with different combinations of useful traits and farmers selected appropriate hybrids to match the environmental conditions on their land.
31
Explain the sequence of events that occur when cross breeding wheat?
In order to crossbreed wheat, pollen is removed from one plant, the male parent, and used to fertilise the ovules of another plant designated the female parent. The first step is emasculation. That is, removing the female plant's own pollen producing anthers to ensure it cannot self pollinate. This head of wheat is being emasculated several days before it's ready to flower. The male anthers are carefully removed, three from each flower.The technician counts the anthers to check that none have been missed. He now has a prepared spike ready for hybridisation. The spike is protected with a bag until the female organs of the flowers, containing the ovules, have time to mature. A few days later, a flowering spike is selected from another wheat variety chosen to be the pollen producing or male parent of the cross.The male parent flowers are cut open. After several minutes, the pollen begins to emerge. The top of the protective bag is removed, and pollen from the selected plant is emptied into the bag and mixed with the original emasculated spike. To protect the pollinated plant, the technician closes the bag to prevent any wind blown pollen from cross contaminating. This guarantees accuracy, and the tag records the data. If the breeding experiment succeeds, the result will be hybrid wheat with desirable characteristics from both parent plants.
32
What is the problem with F1 plants?
hybrids do not breed true; that is, they do not consistently produce offspring that are just like themselves.
So F2 seed (second filial generation) produced by these parents will, once grown, not consistently show the advantageous characteristics of the F1. Within only a few generations the plants will revert to the individual F1 parental types without the desired hybrid vigour. Figure 1.4 illustrates this gradual reversion to less desirable phenotypes.
33
For commercial producers of seed, hybrid plants present a win–win situation; can you suggest why?
For commercial plant breeders, this crucial drawback of hybrid plants is also an advantage; they can sell seeds over and over again, repaying the investment they have made in the breeding technology and making a healthy profit. You will return to this interesting potential conflict of interest a little later on.
For wealthy farmers in high-income countries this tends not to be too much of an issue. Hybrid seed is very costly but rebuying seed every year is worthwhile to ensure high yields. For traditional small-scale farmers in the developing world this is a very significant yearly expense.
34
What is a cultivar?
'Cultivars' is the term given to the varieties of plants which arise from plant breeding and cultivation.
35
What causes the pathogen rust in plants and how does this affect the plant?
Rust was and remains an extremely important plant pathogen. Rust can spread very rapidly and destroy a wheat crop within a few weeks. It is caused by the fungus Puccinia graminis, which weakens the host plant by utilising the plant’s own nutrients to fuel its growth. The wheat eventually lodges (falls over). Combine harvesters cannot then gather the crop, leading to a huge loss of yield.
36
Bearing in mind that naturally occurring rust-resistant wheat varieties do exist, but they are generally very low-yielding and of poor nutritional quality, what plant breeding could be carried out to achieve a useful rust-resistant hybrid? Click on the ‘Edit’ button below and use the response box that appears to type and save your answer.
The rust-resistant variety should be cross-bred with a high-yielding, yet rust-susceptible variety.
37
What is a heterozygous genotype?
Two alleles for a trait are different from each other e.g Bb, Rr
38
What is a homozygous genotype?
Two alleles for a trait are the same as each other e.g. BB, RR, bb, rr
39
What is backcrossing?
Once the two parental plants have been cross-bred together to generate F1 hybrids as you saw in Section 1.2, these F1 plants are then bred with the original high-yielding parental variety. This step is then repeated many times. This is called backcrossing because it is crossing ‘back’ with one of the parental lines. The progeny of each cross is selected and only those that show disease resistance are backcrossed each time.
40
Plant breeders are not interested in the rust-susceptible plants produced from the backcross, but they are interested in the rust-resistant offspring. Unfortunately, inspecting the seeds does not allow the plant breeders to tell which have the resistant phenotype.
How would they tell the two phenotypes apart?
The only way is to grow all the seeds to maturity, infect them with rust and check!
41
After the series of backcrosses and selecting the resistant plants each time, it is possible to achieve the perfect hybrid – a rust-resistant plant but with all the parental characteristics of the original recurrent parent. However, there is a snag. The resistant plants after repeated backcrossing are heterozygous and will not therefore breed true for this disease resistance. It is of great advantage to have plants that are homozygous for this trait.
Can you think of a method in which you could achieve homozygous R R progeny?
Allow the progeny of the final backcross to self-fertilise.
42
Aside from F1 hybrid super seeds what else contributes towards crop cultivation?
Use of F1 hybrid seed gives farmers access to truly ‘super seeds’. But at the same time as F1 hybrids and Borlaug’s rust-resistant crop plants were becoming widely available, other changes in farming practice were making an impact in the high-income countries. By the late 1940s the use of artificial fertilisers and pesticides was increasing dramatically. In addition an increasingly mechanised approach to crop cultivation, coupled with superior irrigation technology, meant that farmers were selecting cultivars that could produce huge yields under these specific growing conditions.
43
The availability of what influences the rate of growth in crop plants?
The availability of fertilisers is one of the most important factors that influence the rate of growth of crop plants
44
What are the most significant 3 nutrients obtained from the soil for the growth of crop plants?
In most agricultural situations, the most significant nutrients obtained from the soil are nitrogen, phosphorus and potassium – the so-called NPK familiar to gardeners from fertiliser packets. Plants also require smaller but significant amounts of calcium, magnesium, sulfur and also some other minerals in trace quantities.
45
Traditionally what did farmers use to restore nutrients back in to the ground? what changed?
Traditional farming methods use animal and crop waste to restore depleted nutrients to soils but the availability of cheap artificial fertilisers to farmers resulted in widespread change to agricultural practices.
46
What else do plant breeders now look for in selective breeds of plant aside from a high yield?
Plant breeders were now selecting for cultivars that have a high yield and:
would grow well under irrigation and with high artificial fertiliser input
would grow to a uniform size so they could be mechanically harvested
could tolerate high levels of pesticide and herbicide.
47
What happened initially to high yielding wheat crops when they were extensively fertilised and how was this resolved?
However by the 1940s and 1950s, the available high-yielding crops were causing problems. Farmers found that if they extensively fertilised their high-yielding plants (and supplied them with sufficient water) they grew so well that the weight of grains in the seed heads made the plants lodge (i.e. fall over) and ruin the crop.
Borlaug, following on from his success with rust-resistance, bred these high-yielding plants with dwarf wheat varieties and succeeded in producing new varieties that were shorter in stature (semi-dwarf) but with stronger stalks (also called straws) that could sustain the larger seed heads. These new cultivars of wheat were semi-dwarf, disease-resistant and highly responsive to fertiliser. And given that stalk growth was suppressed, more of the products of photosynthesis were directed to the grains, improving yield even further.
48
What was the name of the dwarf Japanese variety of wheat used by Borlaug?
Norin 10 was the dwarf Japanese variety used by Borlaug.
49
Describe the advantages conferred by cross-breeding high-yielding tall wheat with the Japanese dwarf variety.
The stem of the dwarf wheat produced from this cross is strong enough to support the weight of the grain and mature without lodging.
50
Some people suggest that the increased yields discussed may not be sustainable in the long term. What do you think is meant by the term sustainable in this context?
Sustainable in this example means in the future it may not be possible to continue to supply the inputs of water and fertiliser needed for the cross-bred plants to achieve their high yields. Sustainability is a widely used environmental concept, which will be discussed further both in Section 3 and in future topics.
51
M. S. Swaminathan suggests that a scientist’s job should not end when they have developed a technology, but only end when the appropriate public policy is in place. Which two of the four module themes (communication, risk, ethical issues and decision-making) are most relevant here?
The use of technology as a tool in foreign policy seems to clearly be an ethical issue. The availability of a specific technology may influence decisions made by one country in the absence of other available solutions. The Indian government for example needed an urgent solution to impending famine in the absence of adequate foreign aid and so was anxious to adopt the new technologies of modern agriculture on offer. In Borlaug they found a scientist who was prepared to work directly with them to achieve these aims. Therefore, arguably, the two most relevant themes are ethical issues and decision-making.
52
What breed of rice was nicknamed miracle rice?
Borlaug’s ground-breaking work with wheat soon spread to other staple crops. In 1962 the International Rice Research Institute (IRRI) in the Philippines produced IR8, nicknamed miracle rice; the first modern high-yielding rice variety ever bred.
Like Borlaug’s wheat cultivars, IR8 is a high-yielding, dwarf variety (Figure 1.11) that produces very high yields if fertilised and irrigated appropriately.
53
Why is the issue of land use for agriculture an important consideration?
Proponents of the Green Revolution claim that without the modern varieties of wheat and rice it would have been impossible to produce the same amount of food without turning over a great deal more of the Earth’s surface to agriculture. This preserves habitats for wildlife and allows maintenance of biodiversity. It also helps to secure nutrient cycling, soil production, climate stability and recreational usage.
54
What reasons could you suggest for the much lower increase in yield of rice IR8 in the countries of sub-Saharan Africa?
Indeed, these high-yielding cultivars rely on significant ‘inputs’: large amounts of water, heavy use of fertilisers and pesticides and suitable terrain soil. These are conditions that are much harder to supply reliably in continental Africa compared to other parts of the globe. These varieties of crop are high-yielding in ‘perfect’ conditions but ‘fragile in a harsh landscape’ (Conway and Sechler, 2000); they lack both the deep roots that would protect them in water shortage and the ability to compete with weeds.
55
What is harvested production?
‘Production means the harvested production. Harvested production means production including on-holding losses and wastage, quantities consumed directly on the farm and marketed quantities, indicated in units of basic product weight.
56
What does a harvest year mean?
Harvest year means the calendar year in which the harvest begins.’
57
What does are harvested refer to?
Area harvested refers to the area under cultivation. Area under cultivation means the area that corresponds to the total sown area, but after the harvest it excludes ruined areas, e.g. due to natural disasters.
58
What does yield mean?
Yield means the harvested production per hectare (ha) for the area under cultivation.
Note that yield is measured in hg ha−1 which means hectogram per hectare, where the hectogram is a unit of mass equivalent to 0.1 kg and the hectare is a unit of land area equal to 104 m2.
59
Are the data consistent with the claim made by proponents of the Green Revolution that the very significant rise in cereal production has not resulted in a significant increase in the amount of land under cultivation worldwide? Make specific references to the data to make your comparison.
Yes and no. Area of land harvested for cereals rose from 1961 to around 1976 where it plateaued for around 10 years and then began falling gradually to a low point in 2002. Since 2002, it began to rise again to surpass the previous peak value.
There has therefore been an overall increase in land under cultivation from 6.5 × 108 ha in 1961 to 7.3 × 108 ha in 2017. Even this relatively small annual increase is substantial and results in loss of ecosystem services. However, the change in land used for agriculture is dwarfed by the enormous increase in yield and production of cereals since the 1960s. The huge increase in yields from 1961 to 2017 coupled to a relatively small increase in area harvested suggest that the modern varieties of crop plants and the technology of the Green Revolution have made these increases in yield possible.
But the Green Revolution had other detrimental impacts on the environment as you will see in the next section.
60
Why was the green revolution considered a good thing if it has sucha damaging environmental impact?
Proponents of the Green Revolution argue that it increased productivity and limited the expansion of land under cultivation. Data from the FAO back up this claim, stating that between 1961 and 2010 the world’s agricultural productivity has risen by between 150 and 200%. However over the same period, there has been an expansion of 12% in the area of land used to cultivate crops, from 1.4 billion hectares to 1.5 billion hectares. Of course, it is very difficult to estimate what the rate of conversion, given the rising population, would have been without modern agricultural methods. Indeed in 1961, 0.45 ha of cultivated land was required on average to feed one person per year. By 2006 this had fallen to 0.22 ha.
61
What environmental impact can the use of water for agriculture have?
Modern agriculture requires intensive irrigation and this can lead to a number of serious environmental and social issues. Abstracting excessive amounts of water from rivers to water crops can lead to reduced river flow, affecting water availability for people downstream and damaging the fish populations that some communities depend on for their livelihoods.
It can result in the loss of wetlands and other important habitats for wildlife and can prevent river water reaching inland seas so they become dry
62
The scientist in Video 2.1 comments that the view of environmental change provided by satellite images is very powerful. What do you think he means in this context?
It is frequently difficult for unaffected people to understand the enormity of the impact of environmental change. The sequence of images shows very graphically how rapid and far-reaching the degradation to the Aral Sea is. They communicate the situation in an easily understandable form, with great impact on the viewer.
63
Video 2.2 views the impacts environmental degradation has on the lives of ordinary people. How effective is this in communicating the significance of the problem?
Seeing the impact environmental degradation has on communities and individuals brings home very clearly how far-reaching the unintended consequences of altered farming practices can be. It is another powerful communication tool to inform the public of the potential damage caused by agricultural practices.
64
What percentage of water put on to land percolates through or flows off? What problems can arise from this?
Typically about 60% of water put onto the land percolates straight through or flows off, raising the water table. As water percolates through the soil it leaches out material including nitrates (often from artificial fertilisers) and pesticides, which can then contaminate watercourses and aquifers. Where it can’t flow away, it can sometimes waterlog the land, reducing its productivity. You will learn much more about the availability of water and its pollutants in Topic 2
Most obvious of all, the provision of water for large-scale irrigation projects involves the loss of land that is submerged behind dams. India built 2000 dams between 1971 and 1989 and 96% of these projects were to provide irrigation. Dam construction inevitably submerges arable land and forest and displaces people, usually very poor people, from their homes.
65
A variety of environmental factors affect the rate at which plants grow.
What environmental factors affect plant growth?
Light, temperature, concentration of atmospheric carbon dioxide, availability of water, availability of nutrients in the soil.
66
What is a limiting factor?
deficiency of just one nutrient will limit the growth of the plant – this is called a limiting factor.
67
Why is nitrogen a key nutrient for plant growth and where do plants get this nutrient from?
Nitrogen is a key nutrient required for plant growth, as it is an important component of proteins. Animals get their nitrogen from plants and plants can only take up nitrogen in a soluble form from water in the soil, normally as the nitrate ion (NO3−). These ions are made available to plants in the soil by a complex series of chemical reactions in which decomposing fungi and bacteria break down dead plant and animal material. Nitrogen in the atmosphere (approximately 79% of the atmosphere’s composition) can be converted to forms suitable for plant absorption by nitrogen-fixing bacteria. These are found free-living in the soil or in the roots of leguminous plants.
68
What is the Haber-Bosch process?
At the beginning of the 20th century a method was found – the Haber–Bosch process – that could convert atmospheric nitrogen and the hydrogen supplied by methane (CH4) into ammonia (NH3). This may then be converted by oxidation into a nitrate that can be absorbed by plants from the soil. As nitrogen (in the form of nitrates) is very often a limiting factor to plant growth, the development of the Haber–Bosch process had an enormous effect on agriculture worldwide. It was a cheap source of nitrate and promoted a massive increase in crop yields, though the initial investment in the process also reflected the need to manufacture nitrogen-based explosives.
69
What is NPK fertiliser?
NPK fertiliser; in addition to nitrogen, this fertiliser contains other important plant nutrients including potassium, K and phosphorous, P.
70
How and why was it profitable and desirable for farmers to supply additonal fertilisers?
Since one aim of agriculture is to increase the production of crop products and to provide an income for the farmer, it is usually desirable and profitable to supply additional plant nutrients in the form of fertilisers. As you have seen, plant scientists during the Green Revolution selectively bred dwarf plants, which are better able to make use of additional nutrients without lodging. Figure 2.2 shows a typical curve for the response of a crop to additions of a typical NPK fertiliser; in addition to nitrogen, this fertiliser contains other important plant nutrients including potassium, K and phosphorous, P.
71
Why, eventually, does adding more fertiliser to plants have no effect?
Availability of soil nutrients is one limiting factor that effects plant growth. Unless other limiting factors such as water availability or carbon dioxide concentration are increased in tandem, after a certain point adding more fertilisers will have no further effect on plant growth.
72
What form are fertilisers in so that plants can take them up quickly?
Fertilisers contain nutrients in a highly soluble form so that crops can take them up quickly. Any nutrients in fertilisers not taken up immediately will be washed out of the soil, ultimately into watercourses or groundwater.
73
What problems to water sources do fertilisers cause because of their high solubility?
Fertilisers contain nutrients in a highly soluble form so that crops can take them up quickly. Any nutrients in fertilisers not taken up immediately will be washed out of the soil, ultimately into watercourses or groundwater.
Determining the amount of fertilisers to add is therefore relatively complex and when fertiliser is cheap, farmers are prepared to err on the side of caution and apply as much as they can to their crop. In the past, over-application of fertilisers has caused significant pollution to waters. Nitrate contamination of drinking water is a serious problem (Altieri,1998). Estimates suggest that 25% of drinking water wells in the USA contain nitrate concentrations above the safety standard. Such levels of nitrate are linked to certain cancers including bladder, oesophageal and gastric. In addition, when fertiliser nutrients enter surface waters they can lead to a phenomenon called eutrophication.
74
How much energy is spent on the production of artificial fertilisers?
It should be noted too that the manufacture of artificial fertilisers is highly energy-dependent, requiring approximately 65 MJ of energy to produce 1 kg of nitrogen fertiliser.
If you are unsure of the units and their abbreviations used here, go to the relevant section of the Primer on the S201 module website.
75
name some traditional means of adding nutrients to, or preventing depletion of nutrients from agriculture land?
Before the use of artificial fertilisers became commonplace, farmers used traditional methods to improve the productivity of their land. Crop rotation was a commonly used technique whereby different types of crops were grown on land each year (Figure 2.3). This can avoid the depletion of nutrients from the soils as different crops make different demands on the land. Growing leguminous plants periodically actually replenishes nitrates in the soil via the action of nitrogen-fixing bacteria in their roots.
Allowing animals to graze and fertilise fields with their manure or using well-rotted compost material from animal and domestic waste.
Allowing land to remain fallow (i.e. without a crop) periodically so the level of soil nutrients can be replenished.
76
what other factors can determine yield of food material aside from fertilisers?
Another factor that can determine yields of food materials is the presence or absence of weeds, pests and diseases (of both plants and animals). In the 19th century it was discovered that certain compounds could be used to control pests and diseases without damaging the crop.
77
What is bordeaux mixture?
A fungicide that uses a mixture of copper sulfate and lime, it is toxic to fish and livestock
78
What does the use of pesticides do to biodiversity?``
Use of pesticides over the decades has certainly increased yields, potentially allowing more people to be fed from a given area of land. But there have been negative consequences for biodiversity. Although more modern pesticides may be highly specific in their targets, the removal of the indigenous plant and animal species (considered ‘weeds’ and ‘pests’ within a crop/herd) disrupts and destroys entire ecosystems. This was highlighted in the book Silent Spring by Rachel Carson (1962), with its vision of a future ‘where no birds sing’.
79
Why is a decline in bee populations of such significance?
Aside from the aesthetic considerations, loss of bees is highly important for agriculture, as they are responsible for insect pollination of crops. Bees pollinate an estimated one-third of all the crops we eat so, as pointed out by Williams et al. (2015), any threat to the welfare of bees is a threat to our agriculture and to us.
80
Give some examples of pesticides that have been banned and the reason for this?
Widespread use of some compounds has unexpected side-effects, sometimes leading to their removal from sale. For example, although DDT was a highly effective insecticide, it also caused thinning of the shells of some bird eggs. Hence, it was one of the first to be banned (first in the USA in 1972), despite its usefulness in controlling malaria-carrying mosquitoes. This is an example of the dual nature of technology, whereby a development such as DDT saved many lives by killing mosquitoes but also resulted in unforeseen negative consequences. Some countries are now using DDT again as the threat from malaria and other insect-borne diseases is considered so great that this consideration outweighs any others.
Another recent example of a problem-causing pesticide is the group of chemicals called neonicotinoids. These are insecticides that are used as seed treatments to protect seeds after sowing from insect pests. There is evidence to suggest that this family of insecticides have a deleterious effect on the nervous systems of bees leading to a serious decline in bee populations. Once again a supposedly selective pesticide affecting only a small range of target pests has been shown to have much greater and more widespread toxicity.
81
What is tillage and what negative impact does it have on the environement?
Tillage is the practice of preparing land for seeds. This involves working the soil to ensure that it is suitable for rapid and consistent germination of the sown seed and so that weeds are removed. Intensive tillage using heavy machinery may have a degrading effect on the all-important organic matter in the soil. This affects soil fertility. Tilling also breaks down the structure of soil, fragmenting the clumps of particles or aggregates and decreasing water permeability.
82
How do machines for agriculture have an environmental impact?
Agriculture is a major cause of soil erosion and highly mechanised farming, with its use of heavy equipment, even more so. Heavy equipment compacts the soil, increasing its density and reducing its capacity to hold water, which can lead to increased flooding.With the increasing use of machinery came the ability to farm at an industrial scale. Machine-farmed fields are huge and such large, hedgeless or ditchless fields are prone to loss of soil by the wind. Similarly, large open fields left bare and uncultivated in winter, or treated with herbicides, lose a significant amount of topsoil. In addition, the soil removed from the land clogs waterways, affecting aquatic species.
Worldwide 75 billion tonnes of topsoil are eroded each year equating to a 9 million hectare loss of productive land
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What drawbacks do F1 cultivars have for farmers?
As you have seen in Section 1.2 the use of high-yielding F1 cultivars has had some significant drawbacks for farmers. These plants cannot be successfully used as seed plants to grow next year’s crop. In the past, farmers routinely saved seed from their highest-performing plants (known as farm-saved seed) to grow next season. However, when F1 plants are used as parents, the offspring or F2 will show significant variation from each other and may not share the desirable characteristics of their parents. This is referred to as not breeding ‘true’. For farmers therefore, reuse means less hybrid vigour and therefore lower yields with every generation.
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Why is it advantageous to use a male sterile version of one of the parental lines?
The male sterile plant is used as the ‘female parent’ that is fertilised by the pollen of the other parent. The female parent cannot make pollen and so cannot self-fertilise; this means that all offspring arising are the product of cross-breeding.
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Why do plant breeders protect their rights in law to restrict the use of farm-saved seed?
They are protecting their own investment into seed production, a time-consuming and expensive process. The seeds are classed as the company’s intellectual property.
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What impact may this protection of farm saved seeds have for farmers in low-income countries?
For subsistence farmers (often small family farms) in low-income countries the world over, the expense of rebuying seed every year has had serious consequences. Many farmers simply cannot afford to use F1 hybrids.
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Prior to the Green Revolution around 30 000 traditional varieties of rice were grown in India (Muir, 2011). Farmers selected the local variety to grow according to local environmental conditions. Farmers, particularly in the low-income countries, would select the exact variety to grow based on their knowledge of their land.
What factors might farmers consider when choosing which seed to use on their land?
They may consider altitude, degree of natural water availability, terrain and local prevalence of plant diseases and pests. The varieties selected would vary even between neighbouring farms; the rich genetic diversity amongst these varieties means that not all the crops in any one year will be vulnerable to adverse environmental effects such as the appearance of a new pathogen or harsh weather conditions.
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Why are 'off the shelf' high yielding cultivars not enough?
After the Green Revolution, many farmers were encouraged to plant only the modern varieties of crop plant with high yields. While these frequently increased harvests in ‘good years’, in poor years – for example when adverse climate events occurred – yields from traditional varieties of crop plant were more reliable year on year. Fortunately, there is now increasing realisation that producing ‘off the shelf’ high-yielding cultivars is not enough.
Scientists must work directly with farmers and use their local knowledge to breed varieties of crop plant that are well adapted to local conditions and to traditional methods of agriculture.
Globally the overreliance on a small number of high-yielding varieties is problematic. There are now only ten highly productive types under cultivation in 75% of all rice fields in India, and in the USA only nine varieties of wheat occupy half of all land growing wheat. This lack of variety puts harvests at risk from unforeseen events, as you will see in the next section.
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Unfortunately, commercial growers are not routinely funding this type of research into local-adapted varieties of crop; can you suggest why not?
The return on this small-scale type of plant breeding is insufficient to be commercially worthwhile. Research in this area generally relies on public sector and charity-based funding.
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What have scientists done to preserve the genes of plants due to the reduced diversity caused by commercially grown crops?
Scientists thought that rust was beaten by Borlaug, but since 1998 the search for rust-resistant wheat varieties has carried on. Central to this work is to identify protective genes in wheat that might confer resistance in the future. These genes could come from cultivars of wheat not commercially grown for decades. Therefore it is in our interest to sustain examples of varieties of all wheat ever grown. So, in the face of reducing biodiversity, no potentially valuable genes are ever lost. To this end, seed bank collections have been established throughout the world to maintain viable seed collection of every variety of crop plant (and wild related varieties) in perpetuity.
To complement the work of the national and local seed banks, an international seed storage facility in Svalbard, Norway (Figure 2.7) was established in 2008 by the Global Crop Diversity Trust. This facility houses seeds in cold storage from every country of the world. It has the capacity to store 4.5 million seed samples.
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Why is the overreliance on a few high-yielding varieties an inherently risky approach?
The genetic diversity represented amongst traditional plants is potentially highly important and must be preserved in case of future need. This resource is ready to fuel future advances in plant breeding. The biodiversity represented by the seed bank gives scientists the capability to ‘breed back in’ characteristics to crops plants that may secure future food supplies.
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Aside from pests and diseases what else is a risk to food security?
Stored seed has already been put to important use. Relatively recently a new virus, grassy stunt virus, threatened rice crops in Asia. After screening 6000 seed bank species, a virus-resistant wild-type variety of rice, Oryza nivara, was identified. This was then cross-bred with existing varieties to produce a suitable new cultivar of rice. But the threat from pests and diseases is only one issue that threatens food security. The threat of climate change suggests that some plant characteristics that are not considered important at present may someday be needed.
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What environmental problems arose as a results of the green revolution?
In her frequent articles on this subject Shiva also identifies several of the pressing environmental issues arising from the Green Revolution. She mentions reduction in crop genetic diversity, problems of monoculture, shortages of water and contamination of soils. These are all issues you have considered already but there are other serious effects of the Green Revolution.
It is suggested that the availability of a range of nutritious food in communities of the low-income countries has been affected, possibly as a result of a smaller range of crops being grown for cash rather than food for the farmers and their families. You will return to this theme of the effect on family diets later in this topic.
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What are the two main arguments for and against the green revolution?
You will notice, even in this tiny sample of the literature on this topic, that there are discrepancies between the claims made by the different protagonists on either side of this debate. Some agencies and individuals think that the Green Revolution was largely a beneficial movement and that, without the wholesale change in agricultural practices, it would have been impossible to avoid widespread famine in the mid to late 20th century. Such groups recognise that environmental degradation was a heavy price to pay but see this as a necessary evil and one that is now being addressed through more sustainable approaches to farming and food production. Others remain vehemently and implacably opposed, believing the sole beneficiaries of the Green Revolution to be the multinational agrochemical and seed companies on whom farmers are dependent for the inputs on which modern agriculture depends. It is difficult to reconcile the opinions with the available data and come to firm conclusions about which side, if any, is actually correct.
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In response to calls for more sustainable approaches in agriculture.
What are the gradual adoption of new practices and reintroduction of old ones for sustainable farming?
minimum tillage and no-tillage farming
crop rotation
reduced water usage
minimising fertiliser application and using the natural fertility of the soil to support plant growth
recycling energy and nutrients on the land rather than adding external inputs
diversification of species cultivated.
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The United Nations (UN) in 2010 defined what three objectives for organic food systems?
Right to food – to grow or to buy where food is available and sufficient to meet needs, accessible both economically and physically and adequate to satisfy dietary needs.
Food availability must be an issue at the level of the household, and supporting small producers to grow food for their communities will have an effect on food security.
Agricultural practice must be sustainable, factoring in maintenance of biodiversity, minimising water use and soil protection.
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For the UN, the environmental impact of agriculture has to be considered alongside a right to access an adequate diet. In order to feed a growing population, we have to address what fundamental questions:
Can the world increase food production and can this be done without irreversibly damaging the environment?
Can our agricultural systems meet the demands of climate change and unpredictable weather events?
Are the techniques we have at our disposal sufficient, or do we need to take further steps to revolutionise agriculture?
In short can we countenance a second Green Revolution?
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What laws are placed on to organic produce?
Many of these approaches are central to the organic farming movement, which outlaws the use of synthetic pesticides and fertilisers and other ‘non-natural’ inputs
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What is genetic modification?
Modern genetic techniques allow plant breeders – using biotechnological techniques – to identify and introduce novel genes from a range of other species into crop plants conferring novel traits which may give the plant advantage. This is genetic modification (also known as GM).
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Why is there a concern over the safety of genetically modified organisms?
However, there are fears surrounding the safety of genetically modified organisms (also known as GMOs) on many fronts – from the effect of eating food derived from such organisms to the risks to the environment from the genes transferring between species.
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Which country are GM crops more common?
GM crops have existed since the 1990s; the technology is already relatively old and yet many countries of the world have not embraced GM crops. Although North Americans have been eating GM food for 20 years, in Europe and Africa GM food is much less common
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How can you define the term biotechnology?
.
The most commonly used technique to bring about this manipulation is genetic modification. GM methods allow scientists to exploit additional variation in plants that could not have been introduced by conventional plant breeding alone.
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What were the first GM plants?
The first GM plants were cultivated over 20 years ago:
1994, the Flavr Savr tomato in the USA (Figure 4.1a)
1998, so-called ‘Bt maize’, an insect-resistant variety, in Spain (Figure 4.1b).
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Figure 4.1 (a) The Flavr Savr tomato, first introduced in 1994 – genetically modified to delay ripening after picking to improve shelf-life. (b) Maize cobs, on the left Bt maize and on the right non-Bt maize. Notice how the non-Bt maize has damage caused by fungi; insect feeding allows the fungus to enter and attack the maize.
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By 2014 what percentage of arable land was producing GM crops?
By 2014, GM crops were grown in 28 countries worldwide with 12% of global arable land under GM cultivation
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What two main issues do GMO crops target?
At the time of writing (2015), the two most common traits that are genetically modified into crop plants are resistance to herbicides and insect resistance. You will be given an opportunity shortly to see if this is still the case. Both these modifications allow farmers to control weeds or insect pests using chemical herbicides or pesticides.the initial development of commercial GM crops focused on the introduction of two traits: herbicide tolerance and insect resistance.
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What other characteristics apart from the two main ones do farmers look for in GM crops?
These traits include characteristics such as resistance to viral, bacterial and fungal infections, drought resistance, stress tolerance (for example to high levels of salt in the soil), changes to flower pigmentation, and modification of plant nutritional content. However, in the 20 years GM plants have been available, herbicide tolerance is still the most common trait modified into crop plants. It will be interesting to see how this changes in the next 10 years.
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What does the genetic material of plants consist of?
At this point you will begin to explore how genetic modifications in plants are carried out. The genetic material of plants consists of the nucleic acid DNA and you will recall from your previous studies that DNA carries ‘information’ in the form of genes that code for the production of specific proteins. Many of these proteins are enzymes that control vital cellular processes.
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What is hoped to be achieved with genetically modifying plants and what is this gene called?
The ability to synthesise various different types of proteins confers different characteristics on organisms. In its most basic form, genetic modification aims to identify and isolate genetic material from one species and transfer it to the species of choice, in the hope that the transferred gene (known as a transgene) will confer the ability to manufacture a particular protein in the recipient. If successful, this will mean that the modified organism can now make a protein that it could not make before and hence will possess the desired new characteristic. Organisms that have been genetically modified in this way are referred to as transgenic.
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Insect damage causes huge losses of agricultural crops each year. For example, without control measures it is estimated that over 35% of current global cotton production would be lost. Insect control by conventional means is big business, and the sale of insecticides generates many billions of dollars of revenue for multinational companies.
What are the drawbacks with continued use of insecticides?
Unfortunately, insects develop resistance to insecticides over time, and this can force farmers to use ever-increasing amounts to achieve control. This increases the costs to the farmers, and deposits even larger amounts of toxic chemicals into the environment (see Section 2.3).
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What are the benefits of plants that are genetically engineered to produce their own insecticides?
If plants could be genetically engineered to produce their own insecticides, the costs and hazards of insecticide spraying might be reduced or removed altogether. The trick is to identify an insect-killing protein or toxin and then find a way of allowing plant cells to manufacture it themselves.
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Explain what Bacillus thuringiensis is and how it can work with a crop as an insecticide?
A bacterial species called Bacillus thuringiensis (Bt) produces such a toxin known as Bt prototoxin (Figure 5.1). B. thuringiensis is an endospore-forming bacterium. Endospores are survival structures formed inside the bacterial cell when environmental conditions become too demanding. This allows the bacteria to survive in a vegetative state until environmental conditions improve. As the bacterium sporulates, it produces crystals of insecticidal toxin that are released with the spore. The isolation of the bacterial gene for this toxin and the insertion of the Bt gene directly into the genome of the crop allow the plants to produce Bt prototoxin in their own cells.
Several crops have been modified to be insect-resistant by incorporation of Bt genes. These include tobacco, tomato, potato, cotton and maize.
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The purpose of ploughing is to reduce the number of competing plants (weeds) in the soil around the crop, although it tends to break up soil structure and leads to increased soil erosion.
What resources are weeds and crop plants competing for?
There is competition for light. Weeds tend to grow quickly and can crowd out crop plants restricting their access to light. Fast-growing weeds also compete for water and for soil nutrients.
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What other difficulties are posed by the presence of weeds within an agricultural crop?
The presence of weeds within the crop may make mechanical harvesting problematic. In addition, weeds can serve as reservoirs for pests and diseases.
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How can herbicides benefit crops and farmers?
Ploughing is also a time-consuming and expensive activity for farmers. Herbicides can selectively attack the weeds that crowd out the crop but are frequently toxic to the crop plants too. Planting crops that are modified to be resistant to herbicides means farmers can plant directly into unploughed soil and freely use herbicides to control the weeds (Figure 5.2) without damaging the crop. Proponents of this technique maintain that this guarantees a weed-free crop and increases yield.
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How are plants made tolerant to herbicide?
A crop can be made tolerant to herbicide by inserting a gene that causes plants to become unresponsive to the toxic chemical. Many herbicides work by inhibiting a key plant enzyme necessary for growth. Glyphosate (also known as RoundupTM) is still the world’s largest-selling herbicide. It is a broad-spectrum herbicide, which can kill a wide variety of weeds. It is particularly effective because it is transported downwards in plants and so has the advantage of killing the roots of perennial weeds.
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What does perennial mean?
Perennials are plants that persist over winter and have difficult-to-extract roots that spread underground.
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How does glyphosate work?
Glyphosate normally inhibits an important enzyme, called EPSP synthase, responsible for the production of some amino acids. Plants treated with the herbicide cannot manufacture the amino acids they need for protein synthesis and this checks growth and leads to plant death. However, some bacterial species naturally produce a version of the EPSP synthase that is resistant to glyphosate. Isolating this gene and introducing it into crop plants results in herbicide-resistant crops.
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What specific bacterial genes are particularly useful when producing GM crops?
So there are specific bacterial genes that code for useful protein products: the Bt insect prototoxin and glyphosate-tolerant EPSP synthase. If these could be inserted into crop plants, they may confer beneficial characteristics that could lead to higher crop yields and/or lower farming costs.
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How to taxonomists name species?
the system scientists use is binomial – every species has two names. The first name is the genus the organism belongs to and the second name denotes the exact species within that genus.
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What is Agrobacterium tumefaciens and where is it found? what disease is it responsible for?
Without the help of a naturally occurring soil bacterium called Agrobacterium tumefaciens, it would be very difficult to insert foreign genes into plant cells. A. tumefaciens (the genus name is abbreviated to its first, capital letter) is the bacterium that naturally causes crown gall disease in a wide range of broad-leaved plants.
Natural infection with A. tumefaciens normally occurs at the site of a wound in the plant. Crown gall disease gains its name from the large tumour-like swellings, or galls, that occur on the stem, branches or roots of the plant after infection.
The galls often occur at the crown of the plant, the point where the main roots join the stem (Figure 5.3a). During an infection, the bacterium transfers part of its DNA into the plant’s cells. Figure 5.3b shows numerous A. tumefaciens attaching to a plant cell wall. The DNA becomes integrated into the plant’s genome causing the plant to produce galls.
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Where are the genes involved in crown gall disease carried in A . tumefaciens?
Most of the genes involved in crown gall disease are not carried on the chromosome of A. tumefaciens but on an extra chromosomal piece of DNA called a plasmid, specifically the tumour-inducing plasmid (also known as Ti plasmid). Plasmids occur naturally in bacteria and consist of circles of double-stranded DNA capable of replicating independently in the cell and of being transferred from one bacterial cell to another (Figure 5.4).
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Plasmids are usually small in size, around 1–20 kb, but the Ti plasmid in A. tumefaciens is significantly larger, between 200 and 800 kb in size. A kilobase (kb) is a length of DNA equal to 1000 nucleotides.
What is a nucleotide?
nucleotides are the building blocks of DNA molecules, which are constructed of nucleotides arranged in a linear sequence. Each nucleotide consists of an organic base, either A, C, G or T, a 5-carbon sugar and a phosphate group.
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What specific traits does the T-DNA sequence of the Ti plasmid of A.tumefaciens contain?
The T-DNA sequence of the Ti plasmid contains genes that code for two specific traits:
tumour-causing genes, which initiate the formation of the gall in the host plant
opine-synthesising genes – opines are modified amino acids that act as a carbon source for the infecting bacteria.
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Name what happens in the sequence when T-DNA of A. tumefaciens affect the host?
The ‘T-DNA transfer functions’ area of the Ti plasmid directs the integration of T-DNA into the host plant genome.
Genes on the T-DNA, when inserted into the chromosomal DNA of the host plant, direct the synthesis of opines.
The opine utilisation area of the Ti plasmid directs the utilisation of opines by the bacterium for its own purposes.
Yet other genes on the T-DNA direct the plant cell to divide in an uncontrolled manner, producing a tumour or gall.
The origin of replication (also known as ORI) is a sequence specific to A. tumefaciens at which DNA copying starts, allowing the plasmid to be copied within the bacterium and then passed on to daughter bacterial cells during cell division.
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How does the natural behaviour of the Ti plasmid of A. tumefaciens lend itself to its use as a vehicle to carry foreign genes into a plant?
If the gene of interest (or goi) could be inserted into the T-DNA region of the Ti plasmid, the natural integration of the Ti plasmid into the plant genome would carry the foreign gene (goi) into the plant, where it could be expressed.
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How are the genes of A. tumefaciens used to put other genes of interest in to a plant and what is this called?
Given that A. tumefaciens is capable of inserting its own DNA into the genome of its plant host, is it possible to insert other foreign genes into the Ti plasmid in A. tumefaciens and allow the normal infective cycle to carry these desired genes into plant cells alongside those of the bacterium? This is in fact just what happens – genetic manipulation allows genes for characteristics of interest to hitch a lift on Ti plasmids and be carried into selected plant cells; this is called transformation. But first, the gene of interest has to be inserted into A. tumefaciens.
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How does a gene gun work?
A. tumefaciens is still routinely used for transforming some plant species but quicker, alternative methods have been sought. One such alternative relies on microprojectile bombardment or biolistics.
In this technique (Figure 5.12), the DNA encoding the desired genes is coated onto inert microscopic particles of gold or tungsten. These are shot into the target plant tissue, using a device called a gene gun (Figure 5.13), in a process analogous to using a handgun at very short range. The particles carry the DNA into the cell and ultimately the DNA dissolves from the particle and is integrated into the plant genome. Though the gene gun is effective in transferring DNA to the plant cell, care is needed to avoid blowing the target tissue to pieces.
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The first types (or first generation) of GM crop plants were marketed at farmers. They addressed issues that made farming less efficient and less profitable.
Which two issues were the most commonly addressed in the early transgenic crops?
Plants were genetically manipulated to become herbicide-tolerant and to synthesise their own pesticides.
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What techniques are used to introduce novel genes into the genomes of crops plants?
Various techniques exist to introduce novel genes into the genomes of crop plants. These include transformation by A. tumefaciens and use of microprojectile bombardment.
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The next card is a summary of topic 1
Lack of food security is a global problem and contributes to political instability.
Advances in agricultural science have enabled the amount of food produced to increase dramatically over the last 100 years.
These increased yields are partly a result of the application of genetics to plant breeding programs; producing superior crop plants.
Current farming techniques in high-income countries rely on heavy inputs of water, agrochemicals and modern varieties of crops, which play a part in environmental degradation.
Expanding the use of these techniques to the low-income and middle-income countries can be problematic for a variety of social and economic reasons.
Conventional plant breeding is insufficient to introduce novel traits in crop plants such as insect resistance and herbicide resistance. This can only be done by genetic modification.
Various techniques exist to introduce novel genes into the genomes of crop plants. These include transformation by A. tumefaciens and use of microprojectile bombardment.
