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In 2010, $30 billion dollars worth
of fruits and vegetables
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were wasted by American retailers
and shoppers
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in part because of cosmetic problems
and perceived spoilage.
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That's a poor use of about 30%
of the produce on the market,
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not to mention the water and energy
required to grow and transport it,
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and the landfill space getting used up
by rotting fruit.
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So what are those cosmetic problems?
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You've probably passed over
a spotty apple in the grocery store,
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or accidentally sunk your thumb
into a mushy patch on a tomato.
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These blemishes can doom produce
to the trash can.
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But what are they anyway,
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and are they actually bad for you?
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Those spots are evidence of an epic battle
between plants and microbes.
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Like humans, plants coexist with billions
of fungi and bacteria.
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Some of these microbes are beneficial
to the plant,
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suppressing disease and helping it
extract nutrients.
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Others are pathogens,
attacking the produce,
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still alive as it sits in a store display
or your refrigerator
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and syphoning off molecules
they can use themselves.
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The good news is
they're almost never bad for you.
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These fungi and bacteria have spent
millions of years
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developing strategies to overcome
a plant's immune system.
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But healthy human immune systems
are different enough
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that those strategies
just don't work on us.
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So in a plant,
what does this process look like?
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Microbes can reach plants
in a number of ways,
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like getting splashed onto it
during watering or fertilization.
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Under the right conditions,
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the microbes grow
into large enough colonies
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to attack the waxy outer layer
of fruit or leaves.
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Their target, the delicious sugars
and nutrients inside.
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This type of pathogen often makes
spots like this.
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A clump of bacteria drains the nutrients
and color from the fruit's cells
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making that yellow halo.
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It then moves outward,
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leaving a black spot of dead cells
in its wake.
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Each spot, which could contain
hundreds of thousands of microbes
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is actually caused by a combination
of microbial attack
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and the host defending itself.
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For example, this is the bacterial
pathogen pseudomonas syringae.
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Once on a tomato,
it enters the fruit and leaves,
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multiplies in the space between the cells,
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and produces toxins and proteins
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that allow it to disrupt
the plant's immune response.
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One toxin, coronatine, makes plants'
stomata open up,
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allowing bacteria to enter
more freely.
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Coronatine also activates pathways
leading to chlorophyll degradation,
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which you can see as yellow spots.
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As the bacteria continue defeat
and multiply,
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they start to kill off the plant cells.
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That explains spots,
but what about mushy blemishes?
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Those are usually caused when the fruit
is attacked by microbes
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after it's detached from the plant.
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If the plant is wounded during transport,
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necrotic fungi can infiltrate
through the wound,
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kill the cells,
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absorb their nutrients,
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and leave your food
looking mushy or brown.
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Those spots in particular
can taste pretty bad.
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You're dead
and decomposing tissue, after all.
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But, you can usually salvage the rest
of the fruit.
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The non-mushy spots, like the ones
you typically see on apples or tomatoes,
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are just on the surface
and don't usually affect flavor.
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Of course, microbes that do make us sick,
like E. coli and salmonella,
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can hitch a ride on vegetables, too.
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But because they're not plant pathogens,
they don't typically cause spots.
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They just hang out
invisibly on the surface.
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So it's washing fruit and veggies,
not avoiding the spotty ones,
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that will help you avoid getting sick.
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So the next time
you're at the grocery store,
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don't be afraid
to pick up funky-looking fruit.
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Some stores will even give you a discount.
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Wash them well and store them properly,
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as some produce like apples and cabbages
will keep in the fridge for weeks.
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The spotty ones may not be eye candy,
but they're safe and just as delicious.