Hi there, I'm Mrs. Kemp, and welcome to today's lesson all about plant diseases.

So let's get started then.

Our main outcome for today is I can describe examples of common diseases in plants, how they are spread and ways to reduce the spread.

These are our main key terms for the day.

And if you would like to read those in a little bit more detail, please do pause the video, but rest assured that actually I will go over each one of these as we move through the lesson today.

So we've got four different learning cycles for today.

We've got the tobacco mosaic virus, which is TMV, crown gold disease, chalara ash dieback, and also food security and biodiversity.

We'll of course start with that TMV, tobacco mosaic virus.

So let's just have a little think about what actually causes disease in the first place.

We have met this word before, they're called pathogens and pathogens are able to be spread from one organism to another.

This makes them communicable diseases.

Pathogens can be in different forms then we can have viruses, bacteria, and there are other types of microorganism that also cause disease.

Let's have a look at them in a little bit more detail then we've got some viruses, bacteria, and another type of organism that causes disease can be fungi and we're going to see examples of each one of these in today's lesson.

Remember that pathogens don't just infect plants, but they also infect animals as well.

So onto our first example then of a plant disease.

This one is the tobacco mosaic virus and as it sounds, it is actually a virus and it infects the tobacco plant mainly.

It actually can infect other types of plants as well that are closely related to the tobacco plant, which are tomatoes and cucumbers.

The symptoms include a sort of discoloration, so not its normal nice green colour, but actually like kind of little brownie patches.

You can see it on the image there and because of the way that they appear on the leaves, it gives it a kind of mosaic pattern and hence its name tobacco mosaic virus.

It can also cause the leaves to curl up.

You can see that they have begun to curl up there in the picture.

Why is this a problem then for the plant? Well, do you remember that actually leaves are made up of lots of cells and in those cells we find chloroplast.

Now chloroplasts have got a green substance in them, a diff like pigment that's able to absorb sunlight and harness the energy that is needed for photosynthesis.

Okay, so it's the main place where photosynthesis will take place in a plant.

Photosynthesis remember actually produces sugar for the plant, which it can then use for lots of different cellular processes.

Now because the tobacco mosaic virus actually causes the plant to produce less chlorophyll, which is why it gets that discoloration, it means that plants are not able to photosynthesize as efficiently as they would do normally.

What this will lead to is less growth, okay? So the plant is not going to be able to grow as quickly as it would do normally, which we can think about that when we're trying to grow a crop such as tobacco or cucumber or tomatoes, this is going to present a real problem.

The amount of crop that a farmer has to sell is known as the yield.

And therefore if they have less growth, they will have less yield and they will make less money when they go to sell that crop at a market.

The virus is actually spread then from one plant to another.

When we tend to plant different crops, they actually tend to be very, very close together.

So just the touching of the leaves can mean that actually direct contact can spread that infection.

We've also got a farmer there in the picture and we can see that that farmer might be going from one plant to another to another and they may actually carry that virus on their hands or on their tools and spread it from one plant to another as well.

There's actually no known cure for TMV for that tobacco mosaic virus.

All the farmer can really do is remove some of the leaves that have been infected or actually remove entire plants to try to control that spread from one plant to another.

Okay, onto our first check of the day then.

So how can the farmer reduce the spread of tobacco mosaic virus? A, avoid contact between the plants.

B, treat with antibiotics.

C, remove infected plants or leaves.

D, spray with fertiliser.

I'll give you a moment to think about it, but if you need more time, please pause the video.

Okay, did you think of A, avoid contact between the plants.

And C, remove infected plants or leaves.

Excellent.

Really well done.

Okay, so let's think about in this task now why it's going to be a real problem for a farmer.

Okay, so this is task A.

I'd like you to get your worksheets out so you can record your answer.

If a crop of cucumbers becomes infected with the tobacco mosaic virus or TMV.

Farmers could lose a lot of money, why would farmers lose money? I'll give you a moment to think about it, but if you need more time, please pause the video.

Okay, did you think of the tobacco mosaic virus causes the leaves of the cucumber plant to turn yellow and curl up.

TMV also causes plants to produce less chlorophyll so the plant can't photosynthesize efficiently, which in turn leads to less growth.

The farmer will also have to remove infected plants.

The farmer will have less crop to sell.

This is a word that you can use when you're talking about the amount of crop a farmer could sell, its yield and therefore make less money.

I hope you got that link there and if you need to add a little bit more, please do that now.

Okay, onto our next learning cycle.

This is crown gall disease.

Okay, another example then of a plant disease is something called crown gall disease and it's really, really problematic.

It's actually caused by a bacteria that is found in the soil.

There is an image there as seen through a microscope because obviously they are microorganisms, so we are not going to be able to see those with the naked eye and that is the particular type of bacteria that causes this infection.

You can then see on the other image there of a plant, it's a tree that's growing these really rather strange, bald structures on their branches and this is a type of tumour, so it's a cell from the plant itself that's growing outta control.

It's very, very similar to cancer in animals.

We can also call that tumour a gall, which hence is why it gets its name.

Now, it actually can grow on many plant species.

There isn't just a single host and that tumour will develop, that gall at the site of infection of where that bacteria gets in.

Why it causes a problem then is that just like animals have a vascular system made up of capillaries and arteries to transport our blood around our body, plants also have a vascular system that is able to transport water and also sugar and minerals in the form of phloem and xylem.

Now that vascular tissue is found inside stems, you can see a little slice of a plant there that's been seen under a microscope.

And what happens is that the actual gall itself draws away all that water and nutrients from the rest of the plant by interrupting that vascular tissue and therefore it will reduce the overall growth of that plant because it's feeding that gall or tumour instead.

It is actually spread throughout contaminated soil and if you are using gardening tools such as in that image, you may actually be moving that bacteria from one place to another and contaminating other areas.

Most chemical treatments unfortunately are not actually effective, so therefore they don't work particularly well.

And really the only kind of way of helping the spread of this is to remove and clear infected plants and also to sterilise soil.

If you find that you have actually got an infected plant in that area.

Onto our next check of the day then this one is a true or false.

Crown gall only affects cucumber plants.

Is that true or is that false? Justify your answer.

Cucumbers can be infected by bacteria.

Or B crown gall can infect many plant species.

I'll give you a moment to think about it, but if you need More time, please pause the video.

Okay.

Did you realise that that one was false? Well done and that's of course because it can infect many plant species.

Excellent, really well done.

Let's try another check.

Which of the following would you suggest when treating a plant with crown gall disease? A, remove the infected leaves.

B, spray a chemical onto infected leaves.

Or C, sterilise the soil.

I'll give you a moment to think about it, but if you need More time, please pause the video.

Okay.

Did you realise that you could sterilise the soil? Excellent.

Really well done.

Right then onto our next task.

This is task B.

Again, you can record this on your worksheet.

So first of all what I'd like you to do is draw a picture of a rose stem.

If you're not sure what rose stems look like, there's one in the picture there for you.

And draw your one with crown gall disease and label the stem and the tumour.

Number two, state the type of pathogen that causes crown gall disease.

And number three, explain how the tumour can lead to stunted growth.

I'll give you a moment to think about it, but if you need more time, please pause the video.

Okay, let's have a look then there's a little picture.

Yours might be much better than this one, but we've got our stem and we've labelled our tumour that is growing from the stem.

The type of pathogen is of course bacteria.

And as the tumour develops at the site of infection then, the tumour disrupts the plant's vascular tissue.

You may have written phloem and xylem there if you added a little bit more detail.

And therefore reduces the flow of water and nutrients in the plant, reducing overall growth.

Excellent.

Well done.

If you need to add a little bit more, please do.

So onto our next learning cycle.

This one is chalara ash dieback.

So this is our example chalara ash dieback, and this affects the common ash tree that we find in this country, that is Fraxinus excelsior.

Okay, it's actually native to this country and occupies quite a lot of woodland.

It is one of the most common trees then, but actually it's unfortunately being threatened by this disease, this dieback disease.

You can see on that image there of where we've got an ash tree that has this infection.

Actually what it's got, it's got a lot of its top canopy there actually being removed.

There's no leaves in that top area and it's dying back, hence the name chalara ash dieback.

It's actually caused by a fungus and it starts in this way.

You can see on that image there the little funguses that are starting to show themselves the sort of fruiting bodies.

And what then that leads to later on.

So it first happens, it's infected in the late summer.

We then get a sort of growing of that fungus later on, but then when it starts to grow later, what happens is these brown legions appear on the leaves.

So you can see that little mottled pattern that is got getting on the leaves there.

Also happens on the twigs and the stem.

You can see on the trunk of that tree where that brown patch is appearing.

Eventually that leads to wilting of the plant, so that's sort of shrivelling up and curling up and a dieback of the actual chutes that are sort of the regrowth part of the tree.

Unfortunately, this is really deadly for trees and actually it does lead to death in the majority of cases.

How it's spread then is that actually funguses release something called spores from mushroom like structures and that's what we just saw on the previous image of the little funguses that are sort of grown onto that twig and the spores are essentially able to then float around and wherever they land they can grow into a new fungus and in this case it can actually those spores can hang around in the leaf litter from the previous year ready for the regrowth of new trees.

And it will then any ash trees that are kind of growing at that time.

You can see in that image of that boot disrupting a mushroom like structure.

And you can see the spores sort of poofing out into the air and they can also be kind of carried by the wind in order to spread them out in a woodland area and increase its chances of being able to infect other plants.

That is a completely different example there on the image, but it's a good one to represent what those spores look like.

So a fungal spore is actually the main reproductive unit of a fungus.

It's very, very similar to what a seed is like, so it can become a new fungus just like a seed if in the right conditions can grow and become a new plant.

Okay, so can we order the statements for chalara ash dieback infection? A, brown lesions appear on the twigs and leaves.

B, the fungus releases spores into the air.

C, eventually the infection spreads through the plant and can lead to death.

D, the spores stick to leaves and infect them.

I'll give you a moment to think about it, but if you need more time, please pause the video.

Okay, the first one is that those fungus releases spores into the air.

They then go and stick to leaves and infect them.

Then the brown lesions will appear on twigs and leaves and finally, eventually the infection spreads through the plant and can lead to death.

I hope you got those in the right order.

Well done.

So unfortunately there isn't actually a known cure for this particular infection.

This does seem to be a bit of a common theme, doesn't it? With our plant diseases.

And actually approximately 5% of the population are actually able to withstand the disease potentially because of genetic factors.

So although 95% of trees will be killed by it, there is a small amount in the population that can survive and because of this then we are not advising people to actually remove living trees.

So like with the other infections where we might remove the infected plant, actually what we are thinking is that if we let those ones grow, then any that are able to withstand that infection, actually we might find that the population of ash trees can come back and will have a much more genetically hardy population, so one that will not be infected.

The trees then are essential for habitat of other organisms. They're really, really important in the UK as they do make up the majority of our woodland.

They provide homes and shelter and food for lots and lots of different organisms. So we really do want to try to think long-term, how can we save our ash trees, How we can slow down the spread then? And this is the kind of advice that we would give to people that are visiting woods.

That actually try to park on hard surfaces and not grassy areas.

So if you don't go and park on sort of verges and things like that, you're less likely to pick up any infected material on your tyres.

If you are out biking or walking or driving in areas.

If you get home, try to remove any debris of those twigs and leaves from your tyres, from your shoes and dispose of it.

Therefore, preventing the spread of that into other areas.

Forestry workers then, so people that actually work in the forest.

They could do things like collect fallen ash leaves and twigs and burn them to disrupt the cycle of the fungus because remember that those fungal spores can hang around in the leaf litter where there's all the kind of twigs and stuff until the next season of growth.

Therefore, if we burn them and get rid of them, it's not going to be able to survive.

Okay, onto our next check then this one is true or false.

5% of all ash tree population can survive chalara ash dieback infection.

Is that true or is that false? Can you justify your answer? They have a genetic susceptibility to the disease.

Or B, they potentially have genetic factors that mean they can survive the disease.

I'll give you a moment to think about It, but if you need more time, please pause the video.

Okay.

Did you know that that was true? Well done and that is because they potentially have genetic factors that mean they can survive the disease.

Excellent, really well done.

So let's go on to our next task of the day.

This is task C.

Please open your worksheets to record your answer.

You have been hired as a forest manager.

You have noticed that some of the ash trees become infected with chalara ash dieback.

Can you design a poster to put on the forest entrance to inform people about the disease and how they can help prevent the spread? I'll give you a moment to think about it, but if you need more time, please pause the video.

Okay, let's have a look then.

So the pathogen is a fungus remember? The types of symptoms will be brown lesions on stems and leads.

It can lead to death of the ash trees.

The treatment, unfortunately there is no treatment available at the moment and how you can help to prevent the spread is to clean forest debris from cars and bike tyres, park on hard surfaces are not on the grass.

If you need to add a little bit more to your poster, please do that now.

So onto our final learning cycle of today.

This is food security and biodiversity.

Okay, so let's remind ourselves about food chains.

They always start with a producer.

An example of a producer we've got here is a plant.

Remember that plants are able to photosynthesize, therefore they are able to make their own food in the form of glucose.

And this is the reason that they need to be at the beginning of a food chain.

Plants also provide shelter for many types of organisms as well as food.

And so therefore they're really, really fundamental to any ecosystem.

So we need to make sure that we prevent the spread of plant diseases in order to make sure that we do not disrupt the other animals within that habitat.

Now, food security is a measure of the quantity, so the amount of something.

And the quality, so how good something is.

Of food available to support households, so small, just people living together, but then also whole communities around the whole globe.

In the UK we're actually really used to having fully stocked supermarkets, so we go in and we decide what we want and we can pretty much pick up whatever we want or there might be a very good alternative for us there.

This isn't actually the case around the world and unfortunately even by today that actually a shortage of food in particular areas around the world can lead to starvation and also death.

Okay, let's have a quick check.

What do all food chains start with? A, a consumer, B, a producer, or C, a predator.

I'll give you a moment to think about it, But if you need more time, please pause the video.

Okay.

Of course, it's B, the producer.

Hopefully you got that one right.

Well done.

So let's think about that Food security then.

A very famous example that happened in the 1800s is potato blight, okay? It was a disease that infected potatoes and it was caused by a fungus.

And actually because it was a staple food in that area at the time, it led to a potato famine.

It's actually estimated that 1 million people died of starvation during that famine, so it was a devastating effect on that area.

It's actually really difficult to treat fungal infections in plants.

We've already kind of talked about an example of those, haven't we? But the best way is really to just remove infected parts of the plant.

Another example of a disease that may lead to problems with food security then in modern day is barley powdery mildew.

It's also caused by a fungus and unfortunately it will reduce the equality and quantity of grain that a farmer can sell.

This drives up the prices because obviously if the farmer has less to sell, he's going to have more competition for people wanting that food and therefore the prices rise.

This means that people living in areas where they have not as much money, it means that they're not going to have the same access to a staple food such as barley.

Barley is actually found in many things like cereals and bread, and so it's really important as a staple food for people.

Often crops then that we grow are often very genetically similar or sometimes identical to one another.

If they're identical, we call them clones, and we also plant them very, very close together.

You can see that lettuce farm just there, and we also gave another example earlier, didn't we, with the cucumber plants that were being grown very close together.

Because of that then, the spread is very easy from one plant to another.

It also means that actually the plant, if it has a genetic weakness, it's likely that all the other plants do as well to a particular pathogen.

And therefore if they get a disease it could wipe out the entire crop.

We call this type of growing a monoculture, mono meaning one.

So it's one type of plant growing in an area.

Which type of pathogen causes the potato famine? Is it A, bacteria, B, fungus or C, virus? I'll give you a moment to think about it, but if you need more time, please pause the video.

Of course it is B, fungus.

Well done.

So despite the complexity of natural ecosystems, the emergence of new pathogens poses the same risk for wild plant communities as well.

In particular, this is chalara ash dieback to our native UK ash tree.

It's actually thought to have originated in Eastern Asia, but since it has managed to get over to this country, actually we're going to lose approximately 80% of all of our ash trees.

It doesn't seem to have any effect on the Japanese ash, and that might be because they have some kind of genetic mutation.

That means they're able to survive.

And actually some of our ash trees are able to survive.

Remember, it's about 5%, and so potentially we might be able to get a genetically stronger plant against this particular disease.

Remember that ash trees provide shelter and food for many other organisms. They are such an important organism.

When we lose ash trees, we also lose a great deal of biodiversity.

Now, let's think about what that word means.

Bio means that it's related to living organisms. Diversity is the variety of things.

Globalisation of the food industry then has really led to a lot of the spread of these plant diseases.

In particular things like seeds being bought over from other countries and the plant material may actually have some of an infection on them.

So when they are moved into this country, it actually means that they are spreading it from one place to another.

Disease is always looked for in any plant material that's being brought over and any that is suspected to have a disease needs to be removed and then safely disposed of.

Okay, onto a next check.

Which ecosystem has the greatest biodiversity? A, B, or C.

I'll give you a moment to think about it, but if you need more time, please pause the video.

Okay, that is C.

Excellent, well done that woodland will have really high biodiversity.

Onto our next task of the day.

Task D, please get your worksheets out to record your answers.

How could you help to improve food security for people of island during the potato famine? I'll give you a moment to think about it, but if you need more time, please pause the video.

Okay, did you think of remove infected parts of the plant and destroy.

The farmers should look to grow another type of plant as well as potatoes to avoid a monoculture.

Make sure that any plant material entering the country is inspected for infections.

And if a disease is suspected, the material should be removed and disposed of.

Excellent.

Well done.

We're very close now, let's just go through our key learning points for today.

Pathogens are microorganisms that cause disease.

Different types of bacteria, fungi, viruses, protists, can all cause disease in plants.

An example of a bacterial disease in plants is crown gall disease.

An example of a viral infection in plants is tobacco mosaic virus.

An example of a fungal disease in plants is chalara ash dieback.

Food security can be threatened by plant diseases that can spread around the world.

The loss of plants can lead to an overall loss of biodiversity in an ecosystem.

I've really enjoyed today's lesson.

I've lots of new information in it.

Thank you very much.

Hopefully see you again soon.

Bye.