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

Today we're going to be looking at Tobacco Mosaic Virus and also Rose Black Spot.

This is from the, "Health and Disease Unit," 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 that spread." These are some of the key terms that we're going to be using today, and if you'd like to pause the video so that you can read them in more detail, please do, but do rest assured that I will be going through each one of these as we move through the slide deck.

We have got three learning cycles for today, Tobacco Mosaic Virus, Rose Black Spot, and Food Security and Biodiversity.

Of course, we will be starting with TMV, Tobacco Mosaic Virus.

So have a little look at this picture here.

What do you think is happening to this plant? So it seems to have quite yellow leaves, doesn't it? And that nice green colour is going a bit yellowy-brown.

And actually the reason why this is likely to be happening is because just like animals, plants need minerals too, in order to stay alive and grow healthfully.

And unfortunately, this plant has probably got a mineral ion deficiency, where it's not able to gain the right amount of minerals from the soil in order to stay healthy.

An example then of a mineral are nitrates and these are used to make proteins which are used for growth and repair.

Without nitrates, the amount of chlorophyll in the leaves is reduced and the leaves become pale and yellow.

Remember, chlorophyll is that green pigment that absorbs light energy to make glucose.

And so therefore, if you've got less chlorophyll, you're going to have less photosynthesis and therefore, less glucose being made for growth.

Plants also need magnesium to make their chlorophyll, and therefore, if they do not have enough magnesium available to them, they're not going to be able to make enough chlorophyll and their leaves turn yellow.

This will also reduce the amount of photosynthesis and therefore, the amount of glucose that a plant can make, and so it will again limit the plant growth.

Now because of the effect on plant growth, if these plants have mineral ion deficiencies, then what the farmer does, he will replace the minerals in the soil by using a fertiliser.

The farmer then may spread that fertiliser onto the field and it could be an organic material such as animal waste, or it could be a chemical composition, that they've got from quarrying rocks.

Okay, let's do our first check of today then.

True or false, without magnesium, plants cannot photosynthesize efficiently.

Is that true or is that false? Can you justify your answer? Plants use magnesium to make chlorophyll.

Plants only need light carbon dioxide and water to photosynthesize.

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 true? Excellent, well done.

And also plants use magnesium to make chlorophyll.

Brilliant, well done.

So as well as these mineral deficiencies, a plant can also get a communicable disease, and this is a disease that is caused by a pathogen and these can be passed from one organism to another.

Things like viruses and bacteria and other microorganisms can be pathogens, okay? And they're not only pathogens, sometimes they can live very safely with other organisms, but the ones that cause disease are known as pathogens and they can infect plants as well as animals.

Today we're really gonna be focusing on the plant ones.

Our first example then is the Tobacco Mosaic Virus or TMV for short.

And we can see a plant in that image, that has been infected with the Tobacco Mosaic Virus.

Now, it doesn't just affect the tobacco plant, but also any closely related plants, such as tomatoes and cucumbers.

So these are the types of plants that people are growing as a crop.

You get a kind of discoloured leaf in a mosaic pattern.

You can see on those leaves that we've got those darker brown spots appearing on the leaves.

It can also cause those leaves to curl up.

We can actually see that happening in that image.

Why is that a problem then? Well, leaves remember, contain loads of cells that have lots and lots of chloroplasts in them.

We can see that in the image that's shown under the microscope.

And chloroplast contain a green substance called chlorophyll.

Chlorophyll is able to absorb light and this provides the energy that is needed for photosynthesis.

During photosynthesis, the plant makes glucose, which can then form other molecules that it can use for its growth.

And if the plant has less chlorophyll then, which happens in the case of plants that have TMV infection, they're not able to photosynthesize as efficiently.

If they're not able to photosynthesize, they won't be producing those sugars, that glucose in the same amount, and therefore, this will lead to less growth.

This will be a problem, as remember, we're talking about plants that we use as a crop.

The amount of crop that a farmer produces is known as the yield, and they can sell this at the market.

If they have a lower yield, they will be selling less and therefore, they will make less money.

This particular virus then can be spread from plant to plant.

We can see in that image there, is some different tomato plants growing together, and they are growing so closely together, to make sure that we're not wasting any space, that they're touching.

And that direct contact can spread the virus from plant to plant.

Also the farmer that is there, they will be moving from plant to plant and they could potentially be picking up that virus and moving it to the plant, and then the next plant and the next plant.

So this is how it would be spread.

There's actually no known cure for TMV, and so really the only thing the farmer can do is to remove leaves or plants that have been infected by the virus and that will hopefully prevent the spread onto other plants.

Okay, onto another check then.

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, "Avoid contact between the plants," which is A, and also C, "Remove infected plants or leaves." Excellent, really well done.

Okay, onto our first task of the day then.

And if you want to get your worksheet out, you can record your answers on there.

If a crop of cucumbers, you can see that growing in the picture there, becomes infected with TMV, Tobacco Mosaic Virus, 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 that the Tobacco Mosaic Virus can cause the leaves of the cucumber plant to turn yellow and curl up? It can also cause 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 some of the infected plant and the farmer will have less crop to sell or remember, that term yield, and therefore, make less money.

Excellent, really well done.

So onto our next learning cycle of today, Rose Black Spot.

So here is an example of a plant that has been infected with Rose Black Spot.

It does affect just roses, and it's caused by a pathogen and that pathogen is a fungus.

You can see in the image that it's got little tiny purple or black spots that have appeared on the leaves.

And sometimes those spots can then get a yellow ring around the outside of them.

Eventually, this can lead to the leaves actually falling off from the plant.

The black spots then actually limit the plant's availability to photosynthesize, okay? Because that chlorophyll is not available in those spots.

This will mean that they will produce less glucose and therefore, this will reduce the growth and development of those roses.

Which pathogen causes Rose Black Spot? 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.

Okay, did you realise that it was a fungus? Excellent, well done.

How is this fungus spread then? So when it grows on the leaves, if those leaves get splashed with some water, let's say there's lots of rain, get lots of rain in the UK, so this would happen all the time.

Then actually that can transfer that, the spores from the plant out into the air and then they can actually fall onto other plants.

It might also happen through wind and also the transfer from gardening tools going from one plant to another.

So what actually is a fungal spore? It's the main reproductive unit of a fungus.

It's very similar to a seed, so wherever that fungus lands, it could grow into a new fungus.

Just like if you planted a seed and the conditions were right, it would grow into another plant.

The fungus can actually lay dormant over the winter in leaf litter, so leaves that have fallen off the plant and also in young stems. And you wouldn't actually realise that it was there, you wouldn't be able to see those spores.

They're teeny tiny.

But after the winter, they would then have their growth and they would infect the new plants.

There's actually no known cure for Rose Black Spot.

You can use fungicides to help keep the infection under control in your plants.

A fungicide then, let's think about that word in a bit more detail.

Fungi meaning the fungus essentially, and -cide on the end of any word, is a killer, so it means killer.

The fungus is ever evolving unfortunately, and so it's having lots of genetic mutations that are happening, changes in its gene, and it's becoming resistant to some of the fungicides.

Also, the fungicides in themselves are quite expensive.

The farmer could potentially try to grow crops that are more resistant to the fungus, so naturally resistant or they could turn to using genetically modified plants that have had a gene moved into them from another organism that has a resistance to that fungus and hopefully then wouldn't be killed by the fungus growing on it.

So farmers and gardeners can also help to slow down the spread of infection.

The thing that they can do is they can remove infected leaves from the plant and they should also collect up any of that leaf litter, those fallen leaves during the autumn and destroy them.

They should also make sure that they are keeping their gardening tools nice and clean and sterilised to avoid spreading that fungus onto other plants.

Onto this check then, it's a true or false.

A farmer could use an insecticide to kill the fungus that causes Rose Black Spot.

Is that true or is that false? Can you justify your answer? The suffix -cide means kill, or B, fungi are not insects.

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 is false? And that's because the fungi are not insects.

Insecticide is a something that kills an insect and not a fungicide that kills fungi.

Okay, onto task B then.

Please get your worksheets out.

You can record your answers on there.

You have taken a job at a garden centre and have been asked to make a leaflet to advise customers on Rose Black Spot.

You should include number one, the type of pathogen, number two, the symptoms, number three, how it is spread, and number four, how to treat infected plants.

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 at what you could have included then.

The pathogen is a fungus.

The symptoms are purple or black spots on the leaves.

The spots may develop a yellow ring around them, and then leaves fall off.

It's spread through the fungal spores can be spread when water is splashed onto the infected leaves or through the wind or transfer from gardening tools.

How it can be controlled then, you can remove infected leaves, collect fallen leaves and destroyed, and there's a possible use of a fungicide to keep that infection at bay.

Hopefully you've done really well on those, but if you need to add a little bit more, please pause the video.

Okay, onto our final learning cycle of today.

This one is Food Security and Biodiversity.

So a food chain, we've met them many a time, actually always starts with a producer.

An example of a producer is a plant, and that is because they can photosynthesize and produce their own food in the form of glucose.

As well as providing food then, they also provide shelter for many different types of organisms that live in that ecosystem.

And that, so it's really important that we ensure that we prevent the spread of plant diseases so that we can make sure that all the animals in that area and other plants have got shelter and they've got food and they can stay free from infection.

Now, for Food Security is a measure of the quantity, so how much of something.

And the quality, how good something is of food available to support households.

So just people living in one home or whole communities.

So villages, towns, countries, and globally.

In the UK, we're very lucky and we're actually used to having fully stocked supermarkets.

If the type of food that we wanted when we went in there wasn't there, there's likely to be a pretty good substitution for it.

Unfortunately, this isn't always the case around the world and actually we still have many areas where there is a real shortage of food and this can lead to starvation and death.

Okay, onto our next check.

What do all food chains start with? A, consumer, B, producer or C, predator? I'll give you a moment to think about it, but if you need more time, please pause the video.

Okay, did you think B, producer? Excellent, well done.

Okay, so let's have a think about an example of a plant disease that actually really threatened food security.

This one is from a long time ago.

It was in the mid-1800s, and it is a plant disease that was caused by a fungus that led to potato blight.

On Ireland, at the time, potatoes were a real staple food, so most people were getting a lot of their nutrients just from potatoes.

And so when this fungus really ravaged all the crops, it led to a potato famine.

It's actually estimated that one million people died of starvation during that famine.

So it really had an effect on the entire population in Ireland.

And even now, as well as then, actually fungal infections in plants are really, really hard to treat.

And really, the only way that you can do that is by removing infected parts of the plant.

And so it really did cause a real problem in those populations living at that time.

Another one that is happening more recently then, so in today's society, is actually a thing called Barley Powdery Mildew, and it is a real concern, because it affects a staple food of barley that is found in many different types of products such as cereals and also bread.

The mildew, the fungus itself, actually what it does is it reduces the amounts of the quantity and also the quality of the grain that the farmer can sell.

What that means is it really drives up prices of barley, and it means that in poorer countries that are struggling with poverty, they can't actually afford to buy the barley in the first place, in order to make the different products.

Now, often when we grow crops these days, we grow them in this way, that we can see on the lettuce farm.

Most of these plants will either be very genetically similar or identical to one another.

If they're identical, we know them as a clone.

They're also planted really, really close together, and we saw that earlier on, when we were looking at the tomato farm.

And when we're growing just this one single type of plant then, we call it a monoculture, mono meaning one.

And the problem with these monocultures then, is first of all, they're very close together, so therefore, diseases will spread really easily.

And also if one of them has got a genetic weakness to a particular type of pathogen, then the rest of them are likely to as well.

So one disease can wipe out a whole crop.

There's really only one way of sort of changing that, and that's to make sure that you're growing different crops.

Okay, which type of pathogen caused the potato famine? Was 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.

Okay, did you realise that that was B, the fungus? Excellent, well done.

So despite what's happening in our natural ecosystems then, actually the emergence of new pathogens is still really, really high risk, okay? So we think about those monocultures being able to be wiped out, but actually in our Ash Woodlands and our Native Ash, actually they're having real problems as well.

It's that tree that we can see in the image and it's a disease called Chalara Ash Dieback.

And you can see that it infects those trees and it kills all of the canopy there.

All those leaves are falling off, and eventually it does lead to tree death.

That disease is thought to have originated in Eastern Asia and then being brought over into this country.

Scientists are predicting that we may lose 80% of our Ash trees in the UK.

However, it doesn't actually seem to harm the Japanese Ash.

And about 5% of our trees are actually able to survive this problem.

So it's thought that maybe some of them, just like the Japanese Ash, have actually got some kind of genetic mutation that means that, that disease is not able to kill it.

So instead of removing the plants in this case, we're leaving them to grow.

And so hopefully, one's that survive will then be able to repopulate these woodlands.

The Ash trees are actually really important to provide shelter and food for many types of different organisms. And when we lose those Ash trees, we are in a real risk of losing a great deal of biodiversity in those woodlands.

Let's think about what biodiversity means then.

Remember, bio in front of any word, means related to living organisms, whereas diversity is the variety of things there.

So biodiversity is really the amount of different types of organisms that live in an area.

Now, one of the contributing factors to the risk of plant diseases is the globalisation of food industry.

That means food and plant material is being moved around the globe from one place to another.

And the biggest threat is when we bring infected plants and seeds into our country from other countries.

We need to make sure that that plant material is always inspected before entering the country.

And if it's suspected that there is some sort of disease on that material, then it's safely disposed of, maybe burned or incinerated.

Okay, which of these ecosystems do you think 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, did you go for C? That's a natural woodland.

It's gonna have many, many different types of organisms living in there.

Excellent, well done.

Onto our final task of the day then.

Please get your worksheet out.

And you can record your answers on there.

So how could you help to improve food security for the people of Ireland 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 last of all, if a disease is suspected, the material should be removed and disposed of.

If you need to add any more to your answer, please do that now.

We're now into the final stage then, so I'm just going to go through those key learning points that we've covered today.

Plants need minerals to be healthy.

Pathogens are microorganisms that cause disease.

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

An example of a viral infection in plants is Tobacco Mosaic Virus.

An example of a fungal disease is Rose Black Spot.

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 ecosystems. I've really enjoyed today's lesson and there's been lots and lots of new information there.

I hope you enjoyed it too, and I hope to see you again soon.

Bye.