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

We're looking at the tobacco mosaic virus or TMV, crown gall disease and also barley powdery mildew.

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 some of the key terms that we'll be using today, and if you'd like to read those in a bit more detail, please pause the video, but rest assured I will go through each one of these as we move through the slide deck.

We've got four learning cycles for today, the tobacco mosaic virus, crown gall disease, barley powdery mildew, and food security and biodiversity.

We will be starting with TMV, tobacco mosaic virus.

So certain diseases that are caused by pathogens, they're able to spread from organism to organism, and because of that, we call those communicable diseases.

Their pathogens can be viruses or bacteria or other types of microorganism.

Things like our viruses, and our bacteria, other microorganisms might be fungi or protist.

And pathogens are able to infect plants as well as animals.

We often focus on the pathogens that can cause disease in humans, but actually they can infect a wide range of different organisms. The first example of a plant disease then is tobacco mosaic virus.

Of course, it's caused by a virus, hence the name, and it mostly infects tobacco plants.

However, it's not just tobacco plants, it's other closely related plants such as tomatoes and cucumbers.

It causes a discoloration on the leaves and you can see some of the leaves there in the image that have got little brown patches on them.

They form a sort of mosaic picture, which is why it's got that term.

You can also see that those leaves are starting to curl up a little bit, which is also a symptom of TMV.

Now, why is that important? Well, do you remember that actually leaves contain cells that have got lots and lots of chloroplast.

The chloroplast contain a green pigment or substance called chlorophyll, and it's chlorophyll then that is able to absorb energy from light and use that in order to produce glucose during photosynthesis.

The plant uses that glucose for growth.

So unfortunately in the tobacco mosaic virus, when it is causing that disease in the plant, it actually produces less chlorophyll.

Therefore, it's not going to be able to absorb that light in the right amount and therefore it won't be able to photosynthesize as efficiently.

This will of course lead to less growth in the plant.

Now the growth of a plant is really important to a farmer.

The yield, so the amount of plant that a farmer produces, they are then able to sell.

So if they don't have the same amount of yield as normal, so if they had less, therefore they would make less money when they sell that plant at market.

This is obviously going to be important for crop varieties like the tobacco plant, the cucumbers, and the tomatoes.

How is this virus spread then? It's actually spread from plant to plant, and we can see in that image there a tomato farmer and those tomato plants are very, very close together.

They are touching, so that virus can be spread by direct contact between the leaves, but also as the farmer moves from plant to plant, they may also be spreading that virus from one plant to another.

There's actually no known cure for TMV and all the farmer can really do is remove those leaves or infected plants in order to try to control the spread.

Obviously, the more they have to remove, the more of their yield they will also remove.

Okay, let's go onto our first check.

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.

Let's go on to our first task of the day then, task A.

Please get your worksheets out as you can record them on there.

If a crop of cucumbers became infected with 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 we 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 infected plants.

The farmer will have less crop to sell.

Remember I gave you that term, yield, you may have used that and therefore make less money.

Excellent.

Well done.

Okay, onto our next learning cycle.

This one is crown gall disease.

Now, crown gall disease is really a very problematic disease.

It's actually caused by bacteria that we find in the soil.

We can see a little image there from under a microscope of some bacteria.

Bacteria or microorganisms, they're really tiny.

We need a microscope to see them.

When they infect particular parts of the stem or branches, we can see that what happens is this tumour grows.

This is one of the cells in the plant that is growing out of control.

It's a little bit like cancer that we see in animals.

We also call that tumour a gall, hence the name of crown gall disease.

So it can actually infect many plants.

It's not like the TMV that we saw a moment ago, actually, it infects quite a lot of different species.

And we first of all see that tumour growing at the site of infection.

So how does that actually affect the plant? Well, plants just like animals have a vascular system.

We have arteries, veins, and capillaries.

They have other tubes that we call flow and xylem and they carry around water and they also carry around sugars and other nutrients.

What the gall or tumour does then is it actually disrupts this vascular tissue and it draws away those important nutrients and also water from the rest of the plant.

This will reduce the overall growth of the plant itself.

It's spread unfortunately through contaminated soil.

Okay, that's very difficult to control and it will also spread by infected tools.

So you can see some gardening tools there.

They go from one place to another.

They could carry the bacteria from one part of the soil to another part.

The type of treatment then, not many of the chemicals are effective at all, but so really the only thing that you can do is actually remove and clear any infected plants from the area and also sterilise that soil so that it no longer contains that bacteria.

Okay, onto our next check then.

So this one is true or false.

Crown gall only affects cucumber plants.

Is that true or is that false? Can you justify your answer? A, 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 get false? And that is of course, because crown gall can infect many plant species.

Excellent.

Well done.

Onto 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 say C, sterilise the soil? Excellent.

Really well done.

Let's go on to our second task of the day then, task B.

Again, you can record this on your worksheet.

So number one, draw a picture of a rose stem.

Now if you're not sure what a rose stem looks like, I've got a healthy one there in the picture, and I would like you to draw one that actually has crown gall disease and label the stem and the tumour.

I'd like you to state the type of pathogen that causes crown gall disease and also 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, so we can see a very simple diagram there of the stem of a rose plant and also the tumour or gall that is growing on it.

The type of pathogen is bacteria and an explanation for the stunted growth is the tumour develops at the site of the infection.

The tumour disrupts the plant's vascular tissue.

You could have mentioned phloem or xylem there as I had done previously, and therefore reduces the flow of water and nutrients in the plant, reducing overall growth.

Hopefully you got all that right, but if you want to add a little bit more, please do.

Okay onto our third learning cycle of today then.

This one is barley powdery mildew.

So this is a disease that affects the plant barley.

It's actually a cereal grain and it's grown all around the world, including here in the UK.

And it's used in many, many different products.

It's really important to us.

It's actually found for brewing beer.

We also use it to make bread and it's also found in a lot of pet food and also food for livestock.

So the pathogen is a fungus, and you can see in that image there on the leaf, you can see that little white, almost looks a bit like white dust and that's the initial stages of this fungus.

So after about seven to 10 days after infection, you get this small, white, fluffy, gross appearing on the upper surface of the leaf.

They then expand and kind of grow together until you get a real mass of grey and white spores on the leaf surface.

A fungal spore is the main reproductive unit of a fungus.

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

Just like wherever a seed is planted, if it gets the right conditions, it can grow into a new plant.

In some very extreme cases of this disease then, the leaves can end up turning yellow, which we already know is a problem because there's not going to be chlorophyll in that region and therefore the plant's not going to be able to photosynthesize, won't be able to produce sugars for growth.

Okay, can you order the statements for barley powdery mildew infection? A, eventually the leaves may turn yellow, B, small, white and fluffy growths appear on the upper surface of the leaf, C, these expand and grow together giving a mass of grey or white spores.

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 B, small white fluffy greys appear on the upper surface of the leaf.

Then these expand and grow together, giving a mass of grey and white spores.

And finally, A, eventually the leaves may turn yellow.

Excellent, well done.

So barley powdery mildew actually reduces the quality and the quantity of the grain that is produced and therefore the farmer is not going to be able to sell as much barley.

It can actually lead to usually about 15% reduction in yield for the farmer, but it can be up to 40 to 45% of a farmer's yield.

The treatment, there is treatment available in the form of a fungicide.

Fungicide, let's break that word down a little bit so we can understand it.

So the fungi is just relating to the actual fungus itself.

When we have cide on the end of a word, it means killer.

So we've got a fungus killer in a fungicide.

What the farmer would do then is spray that fungicide onto the crop.

The fungus is evolving all of the time and so it's DNA is altering and unfortunately the fungicides are really expensive so they can become resistant to them and then the actual fungicide itself doesn't work.

The farmer could try to grow crops then that are more resistant to the fungus.

So there might be naturally some of those barley plants that are actually able to survive even after being infected.

But sometimes the farmers are now maybe using genetically modified plants that actually have a resistant gene inserted into them so they're able to survive that fungus.

Onto another check, true or false? A farmer could use an insecticide to kill the fungus that causes barley powdery mildew.

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

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

Okay, that one of course is false and that's because insecticide means the insects killer and not fungicide.

So that's B.

Well done.

Okay, onto our third task, task C.

I would like you to get your worksheets out so you can record your answers.

Explain how barley powdery mildew can have a devastating effect on the farmer's yield and profits.

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

Okay, did you think of, barley powdery mildew can reduce the quantity and quality of the barley grain.

This could reduce the yield by 15%, but remember it could be as much as 40 to 45%.

The farmer will have fewer crops to sell, which will impact on their profits.

The farmer will also need to use a fungicide to protect the rest of the crop.

These are expensive and we'll use some of the profits.

Excellent, well done.

So onto our final learning cycle of today.

This is food security and biodiversity.

So here we have a food chain.

And remember, a food chain will always start with a producer.

An example of a producer is a plant, and that is because they can photosynthesize and produce their own sugar in the form of glucose that they can then use to make other types of molecules in their body.

So plants provide food as well as shelter for many other types of organisms. So they're actually really important in an ecosystem.

So it's really good for us to make sure that we understand the spread of plant diseases and how we can limit them.

Food security is a measure of quantity and quality of food available to support households or whole community.

So the quantity means the amount of food that's produced and the quality means how good it's.

And we're not just talking small scale, so in one home, we're talking about whole villages, we're talking about whole countries, we're talking about worldwide.

In the UK we are mostly used to having a fully stocked supermarket, so you can go and get whatever food that you like and if not, you might need to have some sort of substitution, but it's usually pretty good.

This isn't actually the case around the world and unfortunately in a lot of countries there can still be a real shortage of food that can lead to starvation and then death.

Okay, onto another 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.

That is of course B, a producer.

Okay, an example of that would be a plant well done.

Now, an example of where a plant disease has caused a real disruption in that food security is actually a long time ago in the mid 1800s in Ireland, it was potato blight that was actually caused by a fungus.

And at the time most people in Ireland were eating potatoes and it was a real staple food.

So it was really, really important in their diet.

Because the fungus wiped out a lot of potatoes then, it meant that it caused a famine.

It's actually estimated that 1 million people died of starvation during that period.

So it made a massive difference to the population.

It is actually really difficult to treat fungal infections even now.

And actually the best way to treat them is to remove the infected parts of the plant.

Another example is one that we've met already today and that is that barley powdery mildew, and it's actually causing a real problem in today.

And what it's doing is it's reducing the amount and quality of the grain.

And so actually what happens is this really drives up prices of barley because the farmer doesn't have as much to sell.

This means in areas where they are living in poverty, actually these staple foods like barley that produces bread are really, really high in cost and they can't afford them.

It's also found in things like cereals and these are consumed by many people around the country and around the globe.

Now, often we grow crops that are very genetically similar or identical to one another.

It helps us to be sure of what their quality is going to be like.

They're also planted very, very close together.

We also saw with the tomato plants and the cucumber plants, how close they are grown to one another.

This means that it's much more likely that they will actually be touching one another.

So plant diseases can spread quite easily from one to another.

The fact that they're very genetically similar means that if one of them has got a genetic weakness to a particular pathogen, then it means that they probably all do and you can lose a whole crop.

Growing these single types of plant is called a monoculture, mono meaning one.

Okay.

Which type of pathogen caused 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 a video.

Okay, did you think B, fungus? Excellent, that's right.

Okay, so despite the complexity, so how many different things are living in that area of natural ecosystems, they can also be really high risk when a pathogen enters that particular community.

And there is this example here of Chalara ash dieback.

Now this is caused by a fungus that actually infects our UK native tree species of ash.

It's thought to have originated in eastern Asia.

And actually it's having a devastating effects on our ash woodland and it's predicted that we're going to lose 80% of all of our trees.

It doesn't seem to have an effect on the Japanese ash and actually about 5% of our ash trees are able to survive this infection.

So we are not trying to remove ash trees, actually, we're leaving them in place and hoping that there will be enough of a community left so that those trees can grow and therefore bring back our woodlands and they will be more genetically hardy so they'll be able to survive these infections.

The ash trees themselves provide shelter and food for many other organisms in the UK and around the world.

They're really, really important.

And the more ash trees we lose, the greater chance that we are going to lose biodiversity in those areas.

Let's break that word down then and think about it a little bit more.

Bio, means related to living organisms. Diversity is the variety of living things.

So biodiversity are all the different living things in a particular area.

Now, one of the major issues with spreading plant diseases then is the globalisation of the food industry.

Okay.

It's where we are buying and selling seeds.

We are shipping food from one country to another and any plant material that is being shipped needs to be inspected really, really carefully to make sure that it doesn't have a disease on it.

If it does, that plant material should be removed and safely disposed of, so likely to be burnt in order to make sure that we are not releasing that fungus or virus or bacteria onto our natural habitats.

Okay.

Which of the ecosystems 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 think C, that woodland? Yep, it will have loads of different plant and animal species in that area.

Excellent.

Well done.

Onto our final task of the day then, task D, please get your worksheets out 'cause you can record your answers on there.

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, so have you got 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.

Really well done.

Okay, we're onto the final part of our lesson then, we'll go through our key learning points.

So pathogens are microorganisms that cause disease.

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

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

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

An example of a fungal disease in plants is barley powdery mildew.

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

The loss of plants can lead to an overall loss in biodiversity in ecosystems. I've really found this lesson interesting today and there's been a lot of new information.

I hope to see you again soon.

Bye now.