- The way we have to look at agriculture
as we move into the future
is looking at it more as a holistic system.
So you have the plants
and you have the plants that surround it,
you have bugs that visit the plants,
and you also have the microbial communities
that are associated with those plants.
We're focusing on the microbiome portion of it
and trying to harness the beneficial interactions
within that system the best way we can.
(light piano music)
- It's hard to imagine that these vineyards
were nearly decimated by Pierce's disease in the 90s.
- You know, there's been recent research
where they're trying to understand
and combat this disease.
- I can't wait to hear more about it.
What is Pierce's disease?
- It is a vascular disease of grapevines
caused by a xylem-limited bacterium
called Xylella fastidiosa that resides
within the water-conducting tissue of the plants.
- What kind of symptoms do you get
when you've got the infection?
- So you can see these typical leaf scorch symptoms here,
you also have green islands,
which is irregular perioderm development.
The leaf blade has fallen off
at the leaf petiole junction.
The petiole remains attached
and they can become very shriveled,
and that's why we call them matchstick petioles.
And then if you were to look inside the plant,
you would see a lot of vascular occlusion
in the water-conducting tissues.
Hydrolic conductivity is very much compromised
in these vines.
- So how does it spread?
- From plant to plant it requires an insect vector.
We have our classes of native sharpshooters
but we also have an invasive species,
which is called the glassy-winged sharpshooter.
A preferred breeding and feeding host
of the glassy-winged sharpshooter is citrus.
You can see here a vineyard
that is next to a citrus grove
under high sharpshooter pressure
because they get to very high numbers in those citrus trees
and then they fly into the vineyard to feed on the vines.
- What is the history of Pierce's disease?
- Pierce's disease is a recurring problem
here in the Temecula Valley.
It wiped out the industry in the 1940s
and recently in the 1990s with the appearance
of the glassy-winged sharpshooter.
- As a wine grower, how does Pierce's disease
impact your business?
- One of the things we always struggle with
is trying to find the quality grapes that we need
to make the best wine.
We have all these employees that make their living
making the wine, and if we can't supply it
because we don't have the grapes,
then we've lost all this huge economic impact
that just spreads throughout the area.
Can't say enough how important it is
to stay vigilant and keep that disease at bay.
- So it actually has been valued at $100 million
in California.
But it's more about the risk that it can cause
to the wine grape industry.
- So what's the procedure if you do see an infection?
- You have to pull the vine out.
And then once you do that, it's three or fours years
before you get another crop, plus all the expensive
pulling them out and putting in new vines,
so it can get quite costly.
- How we prepare the samples
is we first surface sterilize the plant tissue,
place it in liquid nitrogen,
and we grind it to a fine powder.
Then we transfer the powder to a
Eppendorf microfuge tube,
and the powder is what we use for downstream DNA extraction
and microbial community analyses.
- What was your inspiration to study this?
- In vineyards that are under high Pierce's disease pressure
you can have a lot of sick vines
surrounding a healthy vine.
All vines in a vineyard are clonal,
so they're all exactly the same.
And so, the hypothesis was that
perhaps it's the microbial community
that is conferring this tolerance to the disease.
We had a handful of organisms that we wanted to work with
and that we knew we could culture,
and so then we passed those along to Katherine Maloney.
- I'm a natural products chemist
and I was interested in trying to isolate
small organic molecules, chemicals,
that are produced by a fungus,
and in order to do that, the first thing that we need
is a way to test for this activity.
So this is what Xylella looks like,
it's kinda the speckledy appearance.
This is Xylella in the presence of Cochliobolus,
and here you can see that there's no Xylella
to be found on the plate.
So the Cochliobolus completely inhibited
the growth of that Xylella.
And so we were really interested
in that fungus in particular.
So we're operating under the hypothesis
that maybe there's a small molecule,
a chemical, that a fungus is producing
that might be inhibiting Xylella,
and in order to isolate that molecule
we need a way to test that inhibition.
We used a method called column chromatography,
which essentially separated the compounds by polarity.
We tested each of those 10 fractions,
and somewhere in the middle tested positive
for inhibiting Xylella.
The major compound in that fraction was a known molecule.
It's called Radicinin.
So we put different doses of Radicinin
on these filter discs,
but when we up it to 50 micrograms
now we can see the small zone of inhibition
where the Xylella's not growing.
100 micrograms it gets bigger,
so this was pretty compelling data that showed
that Radicinin was responsible for the inhibition.
- So what are the next steps?
- Plants and bacteria and fungi are chemists,
that they make a lot of really cool functional molecules,
and if we can exploit that
to cure things like Pierce's disease,
that's awesome.
- One way could be pre-seeding grapevines
with the beneficial organisms that we discovered
and another is treating vines that are already infected
with Xylella to see if we can cure them of the infection
using natural product chemistry.
- I like the idea that plants, bacteria, and fungi
are natural chemists.
- And you can use that same natural approach
on other crops, like citrus.
- Yes, in fact that's where the agricultural
research community is moving, towards understanding plants
and all their associated organisms, like microbes,
and how that network operates at a systems level
to affect plant health and crop productivity.