AdAgrA 2019: True Success

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AdAgrA: Adventist Agriculture Association

Intensive: Advanced Farmers Only

Michael Trevizo

Plant Pathology - Part 2

So you have to, with all the different diseases, educate yourself in the disease cycle of the different diseases that you deal with.

So if you're somebody that has an orchard or whether you keep an orchard for your, you know, as a hobby or you're actually farming, apple scab is something that you really have to deal with.

So you saw in this video, for 1, they start off in the spring.

And they show you a spore that's on a leaf that has died from the previous year that's on the ground.

Now once the rain comes and that takes off, that puts spores into the air.

Once those spores get in the air, of course, they start to attack new leaves.

And then those new leaves continue to produce more spores, which continue going and going until the whole orchard has been contaminated.

And then of course, you know, at the end of the season develops more parathetiums on the leaves.

The leaves fall off and go to the ground and it sits there until next year.

So by understanding this disease cycle, which is actually, this one's actually late blight.

This is late blight and this is a disease cycle for late blight.

Now, okay, late blight is a very different disease than apple scab, but the important thing is if when you understand the life cycle of the diseases you can understand how you can come in and and interrupt those life cycles right so remember in the beginning I told you that we were to become intelligent and disease its cause its prevention and its cure so Understanding a life cycle is understanding Diseases and what they're looking for so if you can understand the cause if you ascertain this cause is job 26 says Then you can somehow come in and interrupt it and this is yes that's apple scab right there so there's your parathesium there this is referred to this big cycle right here is the cycle that the video first talked about and then it started talking about the conidia force which are right here this is the summer cycle asexual summer cycle The nice thing about the asexual summer cycle is that they're exactly genetic clones.

What's important about that versus a sexual productive cycle?

In an asexual productive cycle, it's exact DNA.

In other words, there's no more new information.

So if you have a genetic resistance to apple scabs So you've got a variety that has it or whatever You don't have to worry about a new pathogen a new race coming out with somehow has developed the capacity to overcome whatever genetic resistance your variety has.

When you have sexual reproduction, that's meiosis, that's new information, you know, that's creating new species or new varieties, I'm sorry, of the species.

So, if I were to take everybody in this room as an example and everybody comes from various different backgrounds and colors and races and nations and tongues and people etc as we're supposed to be as Adventists and we just decide we're gonna breed within ourselves and we keep breeding within ourselves and you go down 7 8 09:10 generations you end up developing a particular type.

In other words, that population that's going to exist is going to be a mixture of everybody's genetics in this room.

So what everybody is, those genes are all going to mix up And what you end up with is completely different people.

Now, let's just say for an example, we're going to do this for this experiment.

I'm going to kill everybody in this room with a green sweater.

So this young man and everybody else is going to die.

And then 2 or 3 of them are born with green sweaters, so we kill those.

And then every generation, we keep wiping it out.

After a while, nobody's going to wear green sweaters anymore.

We're a little more intelligent, but the disease is not that intelligent.

So what happens is that you're selecting?

That's what's referred to as selecting a particular variety.

So we decide that, you know, that's why they call it eugenics.

Or when we go and we try to wipe out a race, like Adolf Hitler did, or Stalin, or over in Uganda, they tried it as well.

When you decide you're going to take this group of living organisms, and you're going to exterminate them, and you only want this other group to survive, that's essentially genetics.

You're saying, I want this to be alive, I want that to die.

So when it comes to this life cycles and diseases and develop and overcoming the genetic resistance that many plants have been bred to have especially with stem rust and bananas are another 1.

What's another 10I know there's another 1.

I can't think of the other ones But anyhow those 3 are 3 world very important world food crops That have an uncertain future in other words They were bred to have genetic resistance stem wheat was bred to have genetic resistance against stem rust.

Well, it's overcome that genetic resistance through Uganda 99 which is a new stem rust that came out in Uganda in 1999 which is why it's called Uganda 99.

And it's spread throughout Africa and it's expected to spread throughout Europe, and Asia, and the Americas, ultimately affecting everybody's ability to grow wheat.

So, and we have no genetics to overcome that.

So, Cavendish, the Mishmichael banana was the first banana that came out in the 20th century, very popular.

It got hit by Fusarium oxysporum, a form of Fusarium wilt.

They came out with genetic resistance, they came out with the Mitchconnell variety which is the banana that we all eat now, that we all come to accept, the yellow 1 that you find everywhere.

It only has genetic resistance against 1 and 2, and partial genetic resistance against 3.

So now 4 has come out, and it came out in Indonesia.

Every single 1 of those banana trees is an identical clone everywhere in the globe.

So it only takes 1 pathogen that can overcome that genetic resistance to wipe out all of the planet's bananas.

It's in Indonesia And I think it just recently was identified in Africa.

And we're expecting it to end up in Latin America, at which point right now, as rich Americans, with respect to the rest of the world, we can still buy bananas.

Because whatever is grown comes to the US, but in other parts of the world Bananas are not as readily available anymore, and that's going to continue to be a problem with citrus We got to deal with citrus canker.

We have no genetic resistance against citrus canker So we've lost a lot of orchards in Florida.

We're losing orchards in Texas, and it's expected to hit in California.

Tons of orchards in Mexico of citrus have gone due to citrus canker, which initially came out through the Mexican Key Line.

So we have no genetic resistance against that.

Again, we're told, we are to be intelligent in disease, its cause, its prevention, and its cure.

And there's more to overcoming disease than just simply genetics.

So if 50% of this room is susceptible to coming down with cancer because you happen to have the diseases that are going to make you sick with cancer, I would hope that you would understand that your genetics only loads the gun.

Your lifestyle choices is what pulls the trigger.

So the genetics is what you're putting in the ground.

How you decide to manage that soil, amend that soil, work with those crops, the environment, the moisture, the nutrition, etc.

That's what's going to pull the trigger for disease.

There's a lot of very interesting things in the world of agriculture.

I'm not going to talk about them today, but All right, so I talked about Overwintering how is the new infection cycle initiated?

We said that that was from the leaf litter, right?

So, you know if you want to minimize, if you have apple orchards and you want to minimize apple scab, 1 of the most important things you need to do is mow down that leaf litter.

Either haul it out of there or mow it down and till it down and get it off the surface of the soil.

When spring comes you don't have to worry about it.

Are spores formed by sexual or asexual processes?

So predominantly they're formed through asexual reproduction which is your polycyclic summer cycle.

But you do end up with some sexual reproduction, new genetics towards the end of the season.

So again you should really, really wipe out those leaves in the summer time, I'm sorry in the fall.

Which flora type is most important economically?

It's definitely going to be the Conidia flora.

That is the reproductive cycle in the summertime that reproduces rapidly and completely inoculates the entire crop now Going into late blight.

I want to go into actually talking about Funguses large portion of what I have to say is fungus because the majority of the diseases that you deal with as a farmer as Anybody producing a crop is going to be fungal related Excluding all your pests insects etc.

I mean there are so many fungal diseases out there.

However, omysete is not technically considered a fungus because it's not actually under the same tree.

Now, I don't believe that the world evolved.

Plant Pathology - Part 3

Timeline of infection is a really important thing.

However in this timeline, we don't actually put You know time as we understand it say a day or a week or a month, etc Some diseases are very slow like filbert blight, You know that that takes a couple of years before you really see it.

Well other things are fast They can be a couple of days.

So the amount of time in between these is is Varies from disease to disease but the important thing is to understand The different steps that these pathogens go through to get into your crop and actually affect it so for fungal pathogens, and it's not that much different for Bacterial pathogens well actually it is Bacterias and viruses they're kind of in a different category.

I'll talk a little bit about bacteria and virus later But for fungus we have a pre-infection stage, which is your germination in other words That's the point where that fungal spore germinated all right, so I remember I got you guys all the way up to the point before we were on the leaf, okay now we're on the leaf.

It's decided that your apple tree is just sick as a dog and it wants to attack it and consume it.

Because, in My opinion, God designed it to do so.

You know, if you ask Darwin, he'll tell you, only the strong survive.

But, what, you know, I mean, different points of view, but at the end of the day, it's serving the same purpose.

So that spore germinates and starts to grow, all right?

Remember in that video, that germ tube started coming out.

It's looking for a good place to drop anchor and In fact when it finds a good place where it wants to be then the a presorium a presorium is formed Which is around around almost peg that will begin to actually penetrate through the cells So that right there these are 2 things in this particular Portion right here you have really you have 3 things that are critical.

1, there are actually different ways like I guess how do I say this?

A lot of research has gone into trying to figure out what is actually signaling to pathogens, hey, I'm a healthy plant, and the other 1 says, no, I'm a sick 1, et cetera.

So there's a lot of enzymes and other things that I'm not even going to go there, but anyhow.

So either the absence of 1 or the presence of 1 signals to the pathogen This is a good place to establish and build a home You know think of the frontiers or the Oregon Trail if you will coming out here They went through what 2000 Miles of Desert before they finally started to see pine trees, and they said let's settle here in Oregon Well, it's kind of the same thing with it's gone through all sorts of different areas all of a sudden It gets to this host and it says wow this is what I've been looking for all my life Let's let's establish here.

So what's going on there is usually associated with plant health so To avoid that crucial step again you go back to soil health Or sometimes its age if the crop is really old and it starts to get hit so really old vineyards old orchards I know they started to pull out a lot of the old vineyards in the southern Willamette Valley that were planted in the 60s and 50s and 40s when they first started to bring the vines into Oregon because it discovered that they were just susceptible to certain diseases so they start ripping them out now they're putting new varieties in Filbert's they're ripping out filberts everywhere, and they figured out how to get genetic resistance Just only partial genetic resistance to filbert blight so now they're putting up filberts everywhere everywhere you look out here.

You see these filbert trees Hardly can't go anywhere, but you know it only has partial genetic resistance in 20 years or supposedly They're going to be attacked just like the ones that are there now, but now That's the host then you have the germ tube search So that germ tube stretches out And it depends on what it is because every fungus is different and every host is different But they have actually discovered that that that the fungus has the ability to actually sense Changes in the topography of the leaf now.

I know that seems strange, but when you're a fungus on a spore I mean when you're a spore or a fungus on a leaf, you know, the leaf could be as to you is like The parking lot of a football stadium.

It's huge So you can really sense changes in topography right because it's just scale So these changes in topography is what dictate, you know, do I want to make an apressorium right in the stomatas?

Or, you know, maybe I wanna go right between these 2 cells over here where the turgor pressure is not right, because maybe your minerals are out of balance, or maybe your moisture isn't right.

Maybe you've dropped stressed your crop too much or added too much water, etc That's what it's looking for then then it starts to set a penetration peg that penetration peg is what actually at this point you will if You will you?

It starts to actually penetrate the leaf and look for a place to form a historium where it starts to actually release toxins into the cell and it starts to actually take nutrients out of the plant or out of the host and it begins to suppress the host system of defenses which is actually just like the plant immune system And then it begins to enter into a reproductive stage so different path it different most Fungal sprays you get whether it's organic or conventional the only thing they're good for is Affecting it somewhere over here Where where these orange you know they vary, but they're here so by the time you have a serious infection most of those sprays are useless It's too late You need to either make your applications post Germination or you're probably not going to be successful, And that's if you're taking that approach.

Now we can talk more, or I'll talk tomorrow more about plant health, but that's for that.

Now, so let's see, getting inside the plant.

So it's very important for the fungal spore which is right there, and you see the Aper saurium comes down through and it's splitting in between the different cells, so what is in between those cells?

The mortar if you will if you understand building brick walls, you know the cement that goes in between the bricks It's mortar that holds those bricks together and makes that brick wall strong Well the mortar in yourselves not only the cells in your body, but the cells in your plant.

It's calcium and silica If it's if it's not in the ground it ain't gonna be there either It's like trying to build a brick wall with no mortar.

So if it's not there, that fungus will come in and say, hey, this is easy street, and just spread out and get in between all those cells, and start doing whatever it's gonna do, but not all of them are that way.

Some of them come in through stomatas or they come in through wounds.

You know, the stomata is where transpiration goes through.

But what's interesting to note is those changes in topographies on that leaf, you realize it's, I don't even know, you probably measure it in angstroms, it's so small.

So again, if you don't have the right potassium in your soil and the right sodium in your soil, you're not gonna have it in your crop.

If you don't have that right sodium and potassium ratios in those stomata cells, the terger pressure may not be the same.

It may be swollen, it may be shrunken, and the crop says, hey, you know, I can get into the stomata even when it's closed very easily.

So proper health, again, goes into that as well.

Then you have through Hydrothodes which are actual I think this is with firms if I remember which is similar to stomata's And then it can also go through Wounds so any damage that is done plants leaves are cut or opened or Could be any type of mechanical damage it can enter through there as well Now here's a more colorful image of the direct attack by a fungal pathogen.

So this essentially is a germ Spore that has germinated and as soon as it germinates these these guys right here These are enzymes that are released cutanase is that are released by the fungal organism.

Essentially, it's like a toolbox, if you will.

Every single fungal spore has this toolbox of these enzymes, which are like tools, that it can release into the immediate environment to break down the waxy cuticles, which is the wax on the surface of your plant leaf.

And then once it breaks that down it starts to actually form that a prosorium in that penetration peg so the first step it needs to do is like you saw in the videos get through that waxy cuticle so what does it need it needs certain enzymes so these waxy cuticles again 1 of the most important things there is copper and zinc Those those things are those other minerals are deficient you don't get the the same strength that you're looking for and then of course once you pass that you get into the right in between the cell the cell walls right here, which again those cell walls are produced are strengthened with Calcium let's see this doesn't this came out kind of Yeah, okay, so this actually is this on the top is the breakout of the waxy cuticle so what you have on top is a wax layer than the wax lamella and then the cutin and the cellulose lamella the pectin lamella the cellulose layer the plasma membrane and then the cytoplasm so it has to get through all of that before it finally gets down to the cell to form a historium How do you how does it do that?

You know first off how does the plant develop healthy?

Cuticles proper nutrition And you know what's funny folks.

Is that this right here that you see if you got athletes foot.

It's no different If you've got different other funguses in your bodies and your nails, et cetera, it's no different.

It's the same when it attacks your body as when it attacks a plant.

So again, This is the same picture as before.

So Again, wow, I thought I'd put this in here already.

We went over this incubation period latent period and quiescent period All right, so fungal infection.

I think this is electron microscope So there's your fungal spore.

There's your a presarium Which is you see it right here now in a black and white it comes through It starts these little circles that you see right there are host oriums that's actually going into the cell and it's looking to hijack the cell and get the cell to work for it it's kind of a way of coming in the back door if you will and I really want to make a point though When I took flat pathology for the first time I was at a secular university, you know Just yeah, it was a secular universe.

I weren't even yeah, it was a secular University all kinds of craziness in there I'll sit in a chair kind of like you guys was a classroom of a couple hundred students and Professor was going off talking about everything I'm talking about and I felt I seriously felt like the Lord was preaching to me because Every time that man described these diseases and how they infiltrated the plant it reminded it really I could see the parallels with how Satan infiltrates the church.

You know, the first layer should be what?

Get everybody to start fighting against each other.

And then start getting them to start feeding him somehow whether it be through bad habits or what have you and I just I just see It and you know Well, you're sitting there think about that think of those parallels because I see it very much in the church and I see it in our homes and and the same way that he you know Ellen White tells us that Satan is the 1 that created these pathogens.

How exactly I don't imagine he came down here and actually I don't know but that's the wisdom that we're given I don't want to make assumptions outside of what we're being told but here again is another image This 1 is going into the stomata.

These are the cells that actually expand and contract to control transpiration in your plant and to bring moisture through the vascular system.

And sometimes you have some that come in through there.

So in this particular case, we're looking at bean rust pathogen forms an apressorium directly over stomata, thereby reducing the need for numerous enzymatic tools, so it doesn't even need that It just comes right in the open door This is again.

I think this is bean rust now This is a similar thing where you have like I was saying that the changes in the topography So you know they're trying to breed for genetic resistance to stem rust they want to make they want to find a way to grow Leaf tissue that's straight flat, so you won't have the infection like that which is You know I don't know I laugh because they put in so much energy and so much effort into genetically engineering and Somehow coming up with these genetics where they can overcome these tricks and a lot of times are really successful at doing that however I mean some of this it just it goes back to nutrition get the nutrition right in the soil and You'll have it figured out now Let's see Kali loas is this is if you're into the organic chemistry, that's what it looks like there is is It's something that the plant puts out to form a papilla, Which is essentially it tries to 1 of the plants Responses to fungal attacks is to try to build a wall a barrier and this is what it uses But if the pathogen has the ability to break that down then It'll break it down and get through so it's just it's almost like a cat-and-mouse game when we start talking about genetic resistance and different host defenses as well as fungal defenses Here's a example of the papilla so in this particular case he had a fungal spore said hey everything's perfect They put out the a presorium it broke down through the cuticles the the host sense that the that the fungus was coming in developed the papilla the Fungus did not have the capacity to break that down the host 1 In other words you have resistance.

This is at the cellular level In other words, this means an expression of DNA, an expression of genetic information.

I'll get into translation and transcription, et cetera, later.

But this is expression of genetic information if you do not have the simple building blocks To express that genetic information in other words the raw materials in other words Plant nutrition, and how you're gonna do this?

Pathogen wins, there's a Hostorium, your crops gonna lose.

Yeah, so then if it develops a hostorium, this is what it looks like.

And it starts producing, sending nutrients off to the rest of the fungus, reproducing, producing more spores in the surface here that launch out like you saw in the video, producing more disease somewhere else.

Plant Pathology - Part 4

Okay, so I talked about oh my koda last time now.

I'm talking about asco my koda So this is the second 1 of the group of funguses that I want to talk about so the big difference now I remember I gave you a very good counsel when I asked you if you really want to learn these things these pathogens I encourage you to get even just a simple compound microscope Or a dissecting microscope something you can get on Amazon for 100 bucks or whatever very high school level early you know first second year of college level Microscope They're available just about anywhere and when you get those microscopes you can begin to look at these things under a microscope And see them under that lens and you begin to see the high for the hyphy in these organisms So what the ask of my the ask of my coda you don't have these these bridges right here that divide that clearly divide the the cells they tend to be straight long hyphes that just go seemingly forever and the Ascomycota you have what they refer to as septate hyphae which means you have these breaks and the hyphae and the hyphae if you don't know what this is, it's essentially the long, thin hairs that grow out of a fungus.

And these are usually all over the forest floor or the soil, et cetera, And they're very complex systems.

They're made out of chitin instead of cellulose so These take different metabolites to break down the cell walls of this ascomycete fungus Let's see their haploid, but that's not really important to you.

So the sexual spores are usually the ascospores, which is a product of meiosis, and then the asexual spores are conidia spores, which is a product of mitosis.

So again, I spoke last time about sexual reproduction, asexual reproduction, the introduction of new DNA information, new species, if you will, or subspecies of varieties, which can oftentimes come over, can, I guess, outcompete the genetic resistance that you might get in certain varieties?

I wanna get into, now Ascomycota's pathogens where the Asco spore plays a prominent role is powdery mildew Apple scab Eastern filbert blight and white mold these are some of the just a few examples of these and asco mycota by the way Is the the group where the majority of all plant pathogen, fungal pathogens are actually Ascomycotas.

Some are oomycete, some are basidiomycete, but the majority are Ascomycota.

So Ascomycota has 3 different fruiting bodies and the reason why this is important because if you were to actually go out and get that microscope I encourage you to buy, you can begin to look at some of this stuff.

And if you look at your primary inoculum on your powdery mildew, you should find a Chasmothecium like this, where powdery mildew began.

That would have been your primary inoculum.

Finding a chasmoethicium is gonna tell you right away you're dealing with powdery mildew, not downy mildew.

And now with apple scab, remember we talked about that parathesium.

You wanna know whether you really have apple scab on your apples or is it maybe a leaf spot or some other pathogen.

You put this stuff under the microscope, you can start to see these organisms.

Now there's apothecium, it's another type of fruiting structure for ascomycetes.

And this is usually associated with leaf spots or not all leaf spots, but maples in particular get this.

So if you're in the ornamental business or the tree business, arborist, have to deal with this 1 the most it's probably 1 of the most annoying pathogens for arborists because they leave these tar spots on your leaves which can be difficult to deal with.

Diseases caused by Ascomycota pathogens where the asexual Spores play a prominent role this group has the largest number of pathogen species relative to the to the Other groups we will look at I think I talked about that here is powdery mildew on grapes Again this is the asco mycota canidia spores is the actual Reproductive cycle that causes this to spread severely throughout your your vineyard This is the canadia spores an actual picture there that you see these spores are the ones that break loose and Keep and they just keep going and going and going they look like a bunch of hot dogs on a string when you put them in a, or a bunch of sausages linked together when you put them under the microscope.

Again, this is a cutaway picture of the powdery mildew.

That's the actual chasmothesium that landed on your leaf surface.

This right here is your cuticles, and you have your epidermal cells You have your mesosheath cells and then etc etc you go to the bottom so that pathogen lands on there It starts producing these hyphes and it produces ultimately conidia force which goes into your secondary reproduction cycle, which just, after that point, it blows up, and you end up with powdery mildew all over the place.

But if you find the powdery mildew at first, which I'll bring up another point that I have not yet discussed today, is the importance of scouting.

I mean if you're farming you got to have somebody scouting whether you're doing it yourself or you're paying somebody to do it.

We're fortunate enough that we're, I literally I can see the University of Massachusetts from the farm so I get the kids that are studying either plant pathology or crop and soil science plant sciences Horticultural etc.

Usually they've gone through courses and learned a couple of tricks so I hire them and they'll just come in and work.

You know, I'd say, hey, I'm very, very flexible.

Whatever hour or 2 you have in the week that you can come in and scout, look at all my crop, and try to find problems.

And they find a lot of problems, and a lot of times they mislabel it, but you know what?

I have had them bail me out a couple of times simply because they told me that they found something that was an issue early on where I could deal with it.

So if you were to actually find powdery mildew when it first comes up, you're gonna find a chasmothecium.

If you've been fighting powdery mildew for 3 or 4 months?

You're gonna find conidiophores, and you might think it's downy mildew, or you might think it might be another pathogen, maybe a leaf mold, et cetera.

But it's very important that you practice scouting for both pests and diseases.

Those are the fungal spores that are coming out of the side of it.

The inside opens up and sets out more spores.

This is the disease cycle for powdery mildew.

I Talked last time about the disease cycle for late blight.

I believe and I talked about the disease cycle for apple scab We're looking at powdery mildew here our initial and overwintering and inoculum again is that chasmothecium that chasmothecium Is what's going to survive the winter and inoculate your crop in the spring and get this pathogen going again in your crop if you?

Have it in there so once it gets going it liberates the asco spores which land on the leaf surface and it takes off A lot of times this chasmothecium is really on the surface of your leaf and these things are really small folks I mean you look at it.

It looks big, but really if you go back to if you're looking at this right here, you're probably looking at that at around 100 to 200x, and you're not actually seeing the spores.

So you got to really go down to about 400 X on a microscope Okay, so we got the disease cycle here.

It starts producing you get infection on roses if you're if you got infections there So again a Powdery mildew like most other funguses are looking for simple sugars.

They're looking for a way to survive like everybody else They want they want to eat they want to reproduce they want to get old and they want to die That's what pretty much in a nutshell is what everybody does on every living organism on this planet does so for them things like leaf petals are hot spots where you can get it sometimes.

The leaf itself, some of the fruit sometimes can be a good place for these guys.

And then they start to come back here and let's see, they go from the leaf petals to the mycelium it forms a chasm of these here It goes to the leaf again, and then you have your overwintering cycle But during before you have your overwintering cycle you have your primary cycle And this is the 1 that goes over and over and over again And it can be within 1 season but usually the 1 that you see mostly wiping out and affecting your crop is the asexual secondary cycle Like I mentioned on the other other ones and I'll keep mentioning that over and over again because that's the 1 you need to try to interrupt Here's apple scab you see all the scabs on the actual apple.

We saw the video if you were here this morning This is is a polycyclic disease the primary inoculum is the asco spores which usually tends to land on the leaf It doesn't land on the apple the apple is content It usually has a apple scab because the spores have been released from the leaf during the secondary Asexual reproductive cycle and then it puts those spores onto your apples Which then contaminate your apples and give you these really ugly apples here Of course, the secondary inoculum is referred to as a conidia and it is a facultative saprophyte.

That means it prefers to live in the world of the dead, but if It has to it'll go on to living tissues, so if you're dealing with a facultative sap sapra fight Then you know that nutrition is probably really an issue Or something is wrong with your fur with your fertilization regimen you're not doing something right and It could be a lot of different things.

So here it is on the leaf This is apple leaves and you see your spores here again Remember I talked to you guys about is it biotic or is it a biotic and this particular example?

You see this is a biotic pathogen and what do you have is really just this blotchiness kind of all over the place.

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Intensive: Advanced Farmers Only

Plant Pathology - Part 2

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Plant Pathology - Part 2

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Plant Pathology - Part 3

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Plant Pathology - Part 4

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Plant Pathology - Part 5

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Plant Pathology - Part 6

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Plant Pathology - Part 1

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