Download SAPS - CSI Trees - Teaching notes

CSI Trees
Technical and Teaching Notes
Teaching Notes
This practical is designed to involve students in a ‘crime scene’ where they try to identify
possible pathogens, and give advice to the landowner. This mirrors the real work performed
in the field by plant health inspectors at FERA (Food and Environment Research Agency)
and DEFRA (Department of the Environment, Food and Rural Affairs), and introduces
learners to the growing implications of plant pathogen spread in the UK.
This activity links into to work from FERA, OPAL and the Woodland Trust, and current media
interest over Ash dieback. It can be used in conjunction with the SAPS Deadly Diseases and
Plant Pathology activity, available from the SAPS website.
This activity can be used across a wide range of ability levels: it ties in to the proposed
GCSE syllabus from 2015i , and can be extended to ‘A’ level (Level 3) or Foundation
Degrees in Horticulture, Landscape Management, Countryside Management or Agriculture.
The beauty of this practical is that it is very low-tech, making it easy to set up in numerous
classrooms, and can be adapted to cover a wide range of pathogens.
Aims of the practical
1. To work in teams to be able to recognise plant diseases in the environment
2. To evaluate the costs to a business of testing for plant diseases, and the larger
implications on the environment
3. To understand how pathogens spread
4. To suggest ways in which a pathogen might be controlled
5. To suggest how plants might defend themselves from pathogens
Safety and biosecurity
Because this practical involves a dead tree as a prop, we would advise against using
obviously infected material in this practical, including ash, to help minimise the spread of
pathogens.
To minimise the spread of plant diseases, all plant material should be disposed of in your
domestic waste route (i.e. ‘black bins’), rather than composted.
We recommend using plant material sourced as locally as possible to your site to minimise
the spread of disease.
Students do not need to touch any plant material during this activity.
Method
Science & Plants for Schools: www.saps.org.uk
CSI Trees: p1

The classroom should be set up prior to the session as a ‘Crime Scene’, with a dead
tree in a pot in the middle of the classroom, cordoned off with hazard warning tape.
Tape could be placed across the door to add authenticity. Tables should be clustered
around the scene to allow small group work.
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Students are issued with lab coats/high vis vests, clipboards & goggles if available to
enter into the spirit of the activity.
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Students sit in small groups around each table and devise questions about the scene
to ask the ‘landowner’ (the teacher, who can also dress the part if they wish!). The
landowner replies to each table’s question to the whole group. It should be stressed
that the learners do not need any specific pathogen expertise at this stage, they are
going through the process of identifying key factors in identifying pathogens.
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Each table is then given a costing sheet, and they decide which tests they would
offer to the landowner.
Extension
This is an opportunity to introduce numeracy, and discuss cost/value analysis, how much is
the tree worth to the landowner, what is the financial impact of not running tests for the
landowner & the wider community. A government paper published in May 2013 is an
especially useful document for post 16 students to read
https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/200396/pb139
06-chalara-socio-economic-framework.pdf
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Depending on the tests that each table chooses, they are given up to two pathology
result sheets. Based on their findings, they are asked to suggest as teams the type of
disease, and what sort of follow up advice would they give to the landowner.
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The correct disease is revealed (Chalara fraxinea), and an information sheet is
issued.
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A discussion is then held on why Ash dieback is so newsworthy, how the pathogen
has been spread, what measures are being introduced to control it.
Apparatus
Per session
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Dead tree (in a pot, so it can be reused)
Yellow/black hazard warning tape
Lab coats/ high vis vests, clipboards, safety goggles
Laminated Landowner ‘fact sheet’
Laminated pathology costing sheets
Laminated pathology results sheets
Handout on Chalara fraxinea
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Extensions
Different pathogens can be looked at as part of an ongoing pest and disease unit. For
horticultural students, this could become a regular 10 minute activity at the beginning of
class, without the props, once the premise has been established to the class.
References and acknowledgements
Dr Charles Lane and Dr Paul Beales. FERA
SAPS Deadly Diseases and Plant Pathology activity:
http://www.saps.org.uk/secondary/science-club-activities/1214-deadly-diseases-and-plantpathology
http://www.stockbridgetechnology.co.uk/horticultural_research/commercial_services/plant_cl
nic/serives_available.php
http://www.forestry.gov.uk/pdf/FCPH-ADD.pdf/$FILE/FCPH-ADD.pdf
Edinburgh Botanic Gardens animation on Ash Trees - http://www.youtube.com/watch?v=HIll_blL5c&feature=youtu.be
Plant Pathology, University of Sydney http://bugs.bio.usyd.edu.au/learning/resources/PlantPathology/introduction.html
This resource was developed by Sarah Owen-Hughes, Askham Bryan College, York after
attending the Gatsby Plants Summer School 2013, funded by an IMPACT award from the
National Science Learning Centre.
iii
Infectious diseases
- recall that bacteria, viruses, protoctista and fungi can cause infectious disease in
animals and plants
- show understanding of how infectious diseases are spread in animals and plants: (to
include a minimum of one common infection, one plant disease, and sexually
transmitted infections in humans including HIV/AIDS)
- explain how the spread of infectious diseases may be reduced or prevented in
animals and plants. To include a minimum of one common infection, one plant
disease and sexually transmitted infections in humans including HIV/AIDS
- recognise and explain the difficulties of controlling infections in plants
https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/211219/GCSE_Sciences_final_up
dated.pdf
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Landowner Fact Sheet
You are responding to the student’s questions, so you may not need to disclose all of this
information. You can embellish or add to these guidelines, depending on your role-play
confidence, but you can really go to town if you fancy character acting!
Some of the information you give is irrelevant to the final result, but is there to show the
students how to sift through for important facts, and how to formulate strong leading
questions. This happens in real life – customers will give a life story with the odd nugget of
useful information hidden in there!
You are a landowner who owns a small (2.5 hectares) woodland of mixed, mostly native
deciduous trees. It is North Facing, towards the East of England, and the site is reasonably
windy.
You don’t do much with it, because the soil isn’t good enough to grow anything else on (it
gets waterlogged), and it is green belt, so you can’t sell it to developers (more’s the pity!).
You inherited it with the rest of your land, and the trees were mostly planted by your
granddad, or have self-seeded.
The soil is a sort of stinky greeny clay, which might be because it backed onto the old
railway line, and you think the lime from the steam train’s water tanks were dumped there.
You don’t get in there much, just a bit of thinning of old wood in the winter, if you have the
time, or to chuck out the local teenagers in the summer who like to camp in there and drink
in the summer. They leave a right mess, but we were all young once!
There’s an old hedge of hawthorn around most of it, and you fill in the gaps with fencing, or
young whips (small saplings that cost about 40p each) which a local environment group
plant for you.
You first noticed some of the young shoots on some of the trees weren’t doing too well a
while ago (don’t know which one, they are all green, aren’t they?!). The leaves are opposite
each other on the branch, and it has black buds in the spring. The leaves looked a bit burnt
late last spring, but you thought that was because of a cold snap. They didn’t pick up, so you
sprayed them with some old fungicide you found in the back of the shed. The label had
come off, and it has probably been outlawed, but you sprayed it anyway. The tips of the leaf
stems have gone brown & continued to die back.
Some funny marks, like stains have started appearing around the branches, and some of the
branches that have fallen to the ground have little mushrooms on them.
You know there is honey fungus on some of the trees in the wood, because of the
mushrooms growing around the base of them, but you don’t think this is the same. Lots of
the trees in the wood are starting to look like this in one area of the wood, and you have
noticed it spreading onto next door’s land. You don’t want problems with him after that
boundary dispute a couple of years ago.
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Plant Pathology Costing Sheet
Laboratory Tests
Cost per Sample
The following tests can be performed on leaves, stems, roots, soil,
fruit or weeds.
Fungal Analysis
Microscope testing of sample, moisture chamber
£100
Bacteria Testing
Including electron microscope, streaming,
£100
Virus Testing
£100
Invertebrate Testing
£100
Nutrient Analysis
Analysis of soil
£25
Pesticide Residue Test
For the detection of various applied pesticides
£80
Plant Pathology Results – Leaves
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Fungal analysis – Visual evidence of Hymenoscyphus pseudoalbidus (Chalara fraxinea)
dieback on leaves, confirmed in laboratory tests
Bacteria testing – no significant bacteria present
Virus testing – no significant virus present
Plant Pathology Results – Stems
Fungal analysis – visual evidence of Hymenoscyphus pseudoalbidus (Chalara fraxinea)
staining on stems, with some samples showing staining through the stem, and necrosis
along the stem rachis. Visual evidence of Armillarea millea (Honey fungus) under the bark
Bacteria testing – no significant bacteria present
Virus testing – no significant virus present
Plant Pathology Results – Soil
Seedling bioassay tests have shown no soil, compost or substrate contamination from
known pesticides.
Soil moisture content showed as an average of 76.25% across the area. This means the
land is wet and boggy, but this should not be an impediment to growth.
Soil pH is 7.9, indicating a highly alkaline soil. This correlates with the suggestion that the
area was a lime dump for the railways.
Plant Pathology Results – Roots
Fungal analysis - significant visual evidence of Armillarea millea (Honey fungus), and
dieback that corresponds with Hymenoscyphus pseudoalbidus (Chalara fraxinea) infection
Bacteria testing – no significant bacteria present
Virus testing – no significant virus present
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Plant Pathology Results – Weeds
No significant atypical weeds were found in the area.
A number of trees showed visual signs of honey fungus infection
Plant Pathology Results – Invertebrates
There were no significant atypical invertebrates found in the area.
Introducing Chalara fraxinea
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Chalara fraxinea or Ash dieback was first recorded in the UK in February 2012 on imported
stock from the Netherlands. It’s distribution is increasing rapidly, and is updated regularly on
the Forestry Commission website http://www.forestry.gov.uk/chalara#Distribution
Known as Hymenoscyphus pseudoalbidus during its sexual stage, there has not yet been
any record of this stage occurring in the UK.
Watch http://www.youtube.com/watch?v=Xf8fll_DWOM (2:16) for a brief history of Chalara
fraxinea from FERA
Symptoms are easier to identify on younger trees, but include necrosis and wilting of leaves
and stems, cankers and staining on stems, epicormic shoots forming on trunks and small
white fungal blooms on infected wood.
http://www.fera.defra.gov.uk/plants/plantHealth/pestsDiseases/chalaraImages/J18201~29.jpg
http://www.fera.defra.gov.uk/plants/plantHealth/pestsDiseases/chalaraImages/J18201~37.jpg
The disease is spread by a number of means: wind carries spores; insect vectors may play a
part; the importation and movement of infected stock; and even the movement of humans
through infected areas.
Watch http://www.youtube.com/watch?v=y1GpufLkBto for a description of symptoms from
FERA.
The impact of this infection on our estimated 80 million ash trees could be enormous in the
UK. Approximately 60 to 90% of Denmark’s ash trees have been lost since 2007.
Ash supports over 100 species of insect, lichens and wildlife.
What impact could the loss of Ash trees have on the British landscape?
Chalara fraxinea is currently a quarantine plant pathogen, so where a tree is found to be
infected, the area will be closed off to the public, and the Forestry Commission can issue
statutory plant health notices, enforcing the removal & destruction of plants by burning or
deep burial on site. No compensation is offered to landowners.
How do pathogens spread?
Fungal spores can be blown for vast distances. If a spore lands on a leaf and there is a
water source, the hyphae will begin to grow. The spore contains all the nutrients the fungus
needs until it is able to penetrate the leaf surface. The spores are touch sensitive and can
feel their way across the leaf surface until they reach a stoma they can enter. The fungus will
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produce a specialised structure, an appressorium, that provides a hold fast platform to allow
the fungus to penetrate the stoma. A thin fungal hypha can then grow into the plant (an
infection peg) and eventually into a cell where it forms a haustorium, a specialised nutrient
absorbing structure.
What modes of transmission do pathogens use to get to the leaves?
Fungi may spread from water droplets or splashes onto the leaves. They may have spores
that lie dormant in soil or in dead leaves. Viruses may be transmitted by vectors such as
insects which may pierce the stem of plants. Aphids, for example use their stylets to suck
sap from the phloem of plants and may spread viruses this way.
Why do fungi infect plants? What advantage do they gain?
Fungi infect plants to gain nutrients from the cells or from the phloem. If they are biotrophic,
as many of the examples looked at are, they invade host tissue but do not kill the plant.
How might this infection affect crop productivity?
As crop productivity is closely linked to the rate at which a plant can photosynthesise, any
damage to the photosynthetic organs would lead to a drop in productivity. If sugars and other
nutrients are also being absorbed by pathogens and pests, then this will allow less biomass
to be made.
What defences do you think a plant might have against pathogen attack?
Protection from a pathogen's initial invasion is achieved via physical and chemical barriers.
Physical barriers
The structure of the surface of many leaves includes the epidermis, a waxy cuticle made
from a polymer called cutin, and stomata. The cell walls of plant cells can also create a
barrier for pathogens. Pathogens produce a range of cutin-degrading enzymes, which may
cause penetration through the cuticle. The thickness of the cuticle, the presence of
secondary cell wall, and the size of stomatal pores can all affect the success with which a
pathogen invades a host. Leaves that lie in a vertical position also help to improve plant
resistance, by stopping moisture films forming on the leaf surfaces, reducing infection by
pathogens that rely on water for movement.
Chemical barriers
Plants can metabolise a great number of different antimicrobial chemicals. Phenols and
quinones are two classes of antimicrobial compounds produced by some plants. Lactones,
cyanogenic glucosides, saponins, terpenoids, stilbenes and tannins are also plant-produced
compounds associated with pathogen resistance. Saponins destroy membranes in saponinsensitive parasites, and are stored in an inactive form in the vacuoles of the plant cell,
becoming active when plant cells are wounded or infected. Defensins are a group of
compounds which interfere with pathogen nutrition and halt their development.
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