Could a virus that just kills plants be the end of us all?

Question

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(Story Plot)

There are two super powers in a "cold war" scenario. One side decided that nuclear war wasn't the only thing they could use to hurt their enemy. Nicknamed The Wheat Eater Virus, its use was (at first) to destroy the enemy's food supply, mainly wheat and rye, very quickly. The virus doses not harm humans nor animals in any way. So when the first wheat crop would start dying off, the climate would be blamed (like a cold snap or a heat wave). Before anyone could find out, it would be too late.

War broke out between the two nations. The virus, that had been fully tested, had no other side effects that were found. So the virus was released by ballistic missile throughout the enemy's country. Both sides retaliated in the world war that followed, and nuclear bombs were also dropped. A ceasefire was called and the nation started to rebuild.

But a strange thing happened: plants all over the world started to die. Not much was known about it at first, and it was blamed on the fallout from the bombs. In time it got worse and plants of all variety were dying (not just wheat). The panic started to set in when all the crops failed; even newly sown fields did not yield anything. Animals were starving, people were starving and canned food would only last for so long. An investigation led to a discovery — the Wheat Eater Virus had mutated and was now targeting all plant life (hinted that radiation did it). The forest, the desert, and even the sea all were affected by the newly named virus, "Life Eater".

(Info)

The Life Eater virus had traits that made it both air and water borne. It would cause total cellular degeneration in the affected plants (the seeds as well) within two days of first infection. The virus is very resistant, withstanding all biomes on earth (snow, desert and water). Upon killing its host, the virus would spread via water and air molecules to affect even more hosts (if it could not find a host it would become dormant). The virus doesn't infect or harm humans or animals in any way. The virus can both live and move in the sea, so plants in the ocean are at risk as well. The world has just come out of a world war (nuclear bombs were used) so the infrastructure is damaged (labs were targets in the war) and attention is not set on looking for a virus. The virus had a few months to spread around the world without detection before it was put on the worlds watch list.

Question: could a virus like this—one that just kills plants—end up killing us, or could we survive?

I'm hoping that I didn't write too much for this question. Just doing a short story and wanted to use a virus trait that hasn't been done before (I hope). As always, if you want any more detail don't hesitate to ask.

Answer 1

We're boned.

You described a virus that is...

• air, fresh, and saltwater borne
• destroys plants and their seeds in two days
• can survive in all terrestrial environments
• can go dormant, presumably in some sort of spore
• does not affect anything but plants
• has been in the wild for a few months

Normally a virus which kills its host in just two days would burn itself out; it would kill its hosts before they could spread the virus further. But by allowing it to go dormant and be transported by air and water, you give the virus a way to spread after killing all the plants in an area.

If this was caught very early, a quarantine could be put in place and the virus could be starved. But in your scenario it's been out for months, and to make matters worse, the Earth's infrastructure has been devastated by a global war, so WHO isn't likely to have the resources nor the cooperation to stamp this out early.

All food (and a lot of everything else) comes from plants

Human food and technology is reliant on two things: plants and petroleum. They both provide cheap energy and cheap chemicals, but only plants provide food.

Plants are the ultimate source of food for (nearly) all life on Earth. They gather the energy of sunlight and store it as energy rich molecules, sugars, which everything else then consumes. With no plants, with no photosynthesis, everything that relies on plants dies. That's (almost) everything.

It's kind of scary to think that we don't know how to make food efficiently without plants. We can transform it with chemistry, heat, and additives. We can feed it to other organisms to make different food. But ultimately we can't make it efficiently without plants. Even vat-grown meat has to be fed.

What's a "plant"?

We should define what a "plant" is and how this wheat virus is suddenly able to kill and reproduce across all "plants". Remember, a virus is basically a bundle of DNA or RNA and a means to get it inside a cell. Once in there it hijacks the machinery of the host to produce itself. This is very specialized and life is very diverse.

Archaeplastida are red and green algae and land plants. This includes sea weed, kelp, and all land plants. It's unlikely that a wheat virus would be able to attack green algae, they're too different.

The kingdom Plantae is basically all land plants. This is still an extremely broad group of species that it's unlikely a single virus would mutate to attack them all.

Instead of evolutionary, let's try functional.

A phototroph is any organism that gets its energy from light. This is everything from cyanobacteria to a giant redwood tree. It's such a diverse group one virus would not be able to use them all as a host.

Maybe it attacks chlorophyll. We can imagine a virus which causes the host to produce a substance which breaks down chlorophyll killing the host. There are several slightly different kinds of Chlorophyll used by land plants, algae, and cyanobacteria. This is very bad as it still winds up killing off just about every phototroph on Earth. It leaves just a few inefficient photosynthetic pigments and proteins.

However, again, it's unclear how a virus would be able to reproduce across such a diverse range of hosts. So while we have a way to kill all "plants" we don't have a way to reproduce the virus using them.

It's really a chloroplast virus!

We can imagine a virus that doesn't attack plants, it attacks the chloroplasts inside the plant.

Archaeplastida (algae and plants) do their photosynthesis in a special organelles called a chloroplast. This is really a little cell within a cell. It has its own DNA and its own reproduction cycle. The plant cell protects the chloroplast, and the chloroplast feeds the plant cell.

This gives us a way that our "plant" virus to attack the whole range of land plants and algae. It might even attack cyanobacteria, since they're so closely related to chloroplasts.

The original virus might have only been able to penetrate the outer plant cell of wheat and grasses, but later devised a way to get itself inside any archaeplastida cell. Once inside, it could attack the less diverse chloroplasts.

What's left?

Any organism which produces its own food is an autotroph and is potentially a source of food for something which can't, the heterotrophs. You and I are heterotrophs.

Non-archaeplastida phototrophs

Basically cyanobacteria. These are found everywhere in the ocean, and on land in a symbiotic relationship with fungi as lichens. There's a lot of cyanobacteria, and it's possible to farm it and use it to feed something more edible like fungi.

If you decide the chloroplast virus also attacks cyanobacteria, that's it. No significant photosynthesizers. No food.

Chemosynthesis

There are chemo-synthetic organisms which derive their nutrients from chemicals. This is no where near as efficient as photosynthesis, so they survive where light is not available, and where there is an abundance of chemicals.

On Earth these are mostly clustered around deep sea vents or live deep inside rock. I doubt they're edible, and I doubt they could sustain a human population.

Fungi... for a little while

Technically not autotrophs, fungi are very good at feeding off other decaying organic matter. And they're edible. For a little while they would have a field day, feeding off all the dead plant matter, but once it was gone they'd also be gone.

The environment goes completely out of whack

Photosynthesis creates sugars made of carbon, oxygen, and hydrogen. The oxygen and hydrogen come from water. The carbon comes from carbon dioxide. In this way photosynthesis pulls carbon out of the atmosphere and locks it up in plants. This acts as sink for extra atmospheric carbon holding keeping the the greenhouse effect stable, the carbon cycle.

If all plants die, all that carbon locked up in plant matter is suddenly released leading to an enormous spike in atmospheric carbon. All the worst predictions of climate change come true: acidification of the oceans, rampant global warming, sea level rise, and extreme weather.

Plants also produce oxygen, but there's so much of that humanity will die of starvation long before it runs out of oxygen, so at least they don't have that to worry about.

A chemotrophic world

No plants means no food. No food means everything that relies on plants for food dies. That's bad news for almost everything alive, but great news for the chemotrophs! With the photosynthetic ecosystems wiped out, they would be able to slowly -- very, very, very slowly -- take over their niches.

Humanity would not be able to survive for long. A single MRE contains about 1200 calories, barely starvation rations. A single person living 60 years would need over 20,000 of them to barely survive. As any fan of Steve MRE knows, even food specially packed for long term storage spoils in a few decades, less if not carefully stored. So it doesn't matter how much food they have stored, it will eventually spoil.

In this world, humanity has a shelf live.

It's possible a few humans would be able to keep small farms alive in sealed environments, but modern biodome experiments have all ended in failure.

The last remaining plants may well be in sealed ecospheres previously sold as nick-nacks. Even those ecosystems are not stable and will die in a few decades.

Answer 2

You wouldn't even need to kill all the plants, if you just killed rice you'd end up doing in most of the human race, a lot through direct starvation but mainly because of the mass migrations and wars that would result. If you killed all the grasses (sorry your idea is not new) humans would get pretty close to extinction, if you also killed off the nightshades I wouldn't give humanity much chance at all, that's almost all the non-tree crops we grow.

Incidentally if you killed off enough grasses oxygen could potentially start getting scarce, oceanic oxygen output is somewhat dependent on silica from the dung of grass eating herbivores on the world's major grasslands.

Answer 3

Assuming that the virus was completely successful in wiping out plants, no, we would have no chance at survival. In reality though, plants are fast adapters and would quickly gain a resistance to the virus. This would happen even more quickly because a large number of insects would also be under intense evolutionary pressure to keep the plants alive. Not only that, but virtually all other plant viruses would be pressured to prevent co-infections! Let's look at a few scenarios:

The virus mutates rapidly

A virus that attacks a large number of plants would need to be very complex. This complexity results in a large genome to incorporate genetic code to attack different plants, and mutations over time would result in the virus diversifying. For example, strains in Sub-Saharan Africa would soon lose their ability to infect the Cactaceae family, which are specific to the New World. Additionally, a fast-mutating virus would quickly evolve to be less lethal. The fact is, it's very difficult to completely wipe out a species with a virus. As soon as the number of targets drop, the virus will be pressured to increase the length of its lifecycle, leaving the plants alive for longer.

The virus has a very low mutation rate

If the virus is engineered to have a very accurate replication in order to prevent it from straying from its original goal, it will quickly become noncompetitive with other viruses and pathogens. If it was the radiation from a nuclear war that caused the mutation that lead it to attack all plants, then as the radiation dies down, mutation rate may drop, after which the primary factor is the accuracy of its replication apparatus. Such a virus would quickly wipe out a large population of plant life, leaving behind resistant plants. The virus' inability to mutate rapidly would lead to it dying off.

The virus is a retrovirus

A retrovirus contains RNA instead of DNA. When it infects a cell, an enzyme called reverse transcriptase converts the RNA into DNA, and an enzyme called integrase inserts that DNA into nuclear genetic material. The virus can have a long dormant period in the cell's genome, and only activate years down the line. Retroviruses are special because small mutations can sometimes cause them to lose their ability to complete their life cycle, turning them into retrotransposons (sometimes called jumping genes). This is so common in evolution that a significant portion of our own DNA comes from such viruses! So what if the virus infects plants in that manner, staying dormant in its genome and allowing it to be passed from generation to generation? While this alone isn't enough to wipe out even close to all plant life, it could easily cause the virus to become virtually impossible to get rid of, and periodic outbreaks could become ubiquitous. That alone would pose an existential risk to humanity, even if all plant species do not go extinct.

Answer 4

Ash's answer lays out some good ideas for how different plant species dying off would end the world, but I'm not certain that it's possible for a plant virus to have the properties you want in the first place. For one thing, they're not usually that deadly. (Tobacco mosaic virus or TMV, a well-studied plant virus, does a tremendous amount of economic damage, but each individual plant is only stunted, not killed. Though expensive, it would be possible to out-produce the losses.) They also have difficulties in transmission vectors. The normal vectors are physical contact between infected plants or through intermediary animals (usually pollinators, grazers, or worms). As far as I can tell, there are no airborne plant viruses - probably fortunately. Since these vectors require plants and animals to be active, it wouldn't be very good at spreading in cold or sparsely-populated areas.

You might want to change the backstory to focus on chemical warfare (chemical toxins won't spread themselves - usually - but once in the ground, they can be devilishly difficult to remove) - or simply say that the plants died and with the world falling into chaos, they never did figure out exactly why.

Answer 5

No. a "kills all the plants" virus would not necessarily kill all humans just 99.999% of us a group with forewarning and/or sufficient resources and dedication (probably either of the superpowers mentioned) could allow a small group of humans to survive until the virus wipes itself out through over-activity if thoose humans really know what they are doing then they could survive this long and then unfuck the planet, at least enough for humanity to live on.

what will this group eat? well there are a few sources:

1. Deep sea fishing, pretty much everything in the very depths of the sea does not depend on sunlight but scavenging from what falls below and on hunting other deep sea life. high pressure fishing submarines (probably robotic) could probably gather a significant amount of food from down their for centuries before even that ecosystem collapses. Even then tube-worms could still be a source of food.

2. Radiotrophic fungi some fungi in chernobyl have shown the ability to survive off only radiation this process is inefficient but a nuclear power could if they so wished dedicate a significant number of resources towards building a "farm" of these that could feed a significant number of people and last many years. if our survivors have a nuclear reactor (a near certainty if its a government effort) they could even use its vitrified waste to expand theese efforts

3. processed fossil fuels while not necessarily a great addition to the human diet and certainly providing no vitamins/minerals/fibre/protein etc...can be made into edible calories in the form of simple carbohydrates like alcohol. many of the facilities required to do so already exist in petrochemical plants and are simply not being used for this purpose

4. (for the first few years at least) the slowly rotting carcasses of everything else, bone marrow locked away in their skeletons and the remaining canned food. ideally large scale "moving edible stuff to the south pole and burying it in 40 ft of snow" operations would be set up.

5. recycled dietary fibre (no i will not go into more detail) though that obviously won't provide calories.

to clarify these people will not be healthy, they will not be happy, they will most likely be under military rule with little freedom and they might be a tiny bit imbred but they will be alive. but the aim is that at some point conditions will improve and their descendants will carry on the human race.

the biggest problem for such a group would not infact be the the lack of food (that's immensely hard to deal with but not impossible) but the release of almost all of the 4*10^12 tonnes of carbon in the earths biosphere over the next ten or so years. Comparing that to human CO2 emissions and you're looking at well over three hundred consecutive "2015's" worth of human CO2 emissions being dumped on the planet, this has serious potential of causing a green house effect. there is however a simple solution to this! since you're no longer earth's ecology you can just enter all of earth's nuclear missile silos and detonate the warheads creating a nuclear winter to "cancel out" the green house effects. this is just a short term solution though you'll either need plants to start growing again or some other way of getting rid of those green house gases (I recommend self replicating robots).

fallout from the bombs would likely not be a problem after a hundred years or so. Futhermore any remaining life would likely evolve increased radiation resistance humans would avoid the radiation simply by planting their bombs in the right places, by filtering air and water and by minimising exposure to the 'outside world'. global dimming would be a problem for any remaining plants however it will be minimised by the lack of competition, and abundance of CO2.

there is a good chance that at least one plant survived and will then spread once more other the earth. if not theres always the Svalbard seed vault. a lot of what i've described requires an industrialised society which obviously would be gone by this point however its possible that with sufficient preparation the necessary technologies could be salvaged and its likely that if the lives of all N hundred people left are dependant on their running they will continue to run.

this of course requires a competent government however but in general governments can, in times of crisis, be relied upon to get all their stuff in one sock install somekind of military junta and do what needs to be done. the number of people that could survive is really dependant on how long the virus takes to kill everything and how willing the government in question is to devote valuble manpower into this project. best case scenario the virus takes decades to come to full fruition, all the governments work together, new tech is developed and perhaps a small fraction of the population is saved. worst case scenario its one crazy general who saves a hundred people for a decade or two before everything stops working and mankind dies off for good. if i had to guess? i'd say ten-thousand people could be saved if done right.

Answer 6

There are several alternative food sources, that could allow for rebuild afterwards.

Mushrooms and fungi can serve as a nutrition source, and hell is there a lot of dead plant matter for them to feed on after the plantopalypse.

Back in the days of yore there were huge fungi on the earth, I imagine the same will happen again with the rich nutrition soil available to them.

Then there are insects. Gods are there insects. Not the nice pollinators, they'll die. Goodbye bees, goodbye butterflies. But the mulch eaters, roaches, woodlice, etc... Fancy a nice roach burger?

Also, just as the virus has adapted, some plant life will also adapt. It's very very hard to get 100% eradication or success. Hence Monsanto, Bayer and the other poison manufacturers have to keep improving their poisons. There will be a few hardy plants that'll survive because they're different, get a defense for the virus, that could lead to a rebound in a few hundred/thousand years.

Also, assuming this is seen worldwide as a "Real ****ing problem" that will push aside all differences, and causes worldwide collaboration on fixing the issue.

They identified that it's a virus so they still have viral labs, they'll set quickly on establishing labs finding its weaknesses/attachment proteins and modifying plants that don't have those with worldwide cooperation. I will assume billions of moneys will be spent on making this happen "F.A.S.T."(Find Alternative to Starvation Threat). Because everyone is sick and tired of Roasted mushroom with a woodlice sauce on a bed of cockroaches after a few years.

How would these plant labs operate?

They completely isolate seed vaults with very very strict sanitizing procedures to enter or leave.

All material will be blasted with gamma rays to kill any traces of the virus, the material will only be released when the grass placed with the material in quarantine survives for a week after good air circulation and exposure to the material.

Then they set up their virus manipulation labs near there to modify the precious seeds to survive the virus by eliminating attachment points where the virus can attach.

They'll release these plants in the wild, so they can evolve further in nature to became hardier against the virus. All iterations get tested in the wild and what sticks is allowed to spread further and further, making sure as much of the world gets their "patch of green" to allow it to spread and germinate and adapt as quickly as possible.

So by using mushrooms as alternative food sources, a select few animals can be preserved that can digest them.

Small animals will be bred to be able to eat and digest them, a lot of animals will automatically run to the bountiful mushrooms to start eating them instead of plants. Those that survive will be the basis for the new natural order. Nature will find animals to fill the abandoned spots in the life cycle.

There will be mass extinction of many species, but a lot of herbivores in moderate climates will survive, especially if human aid is provided by teaching the animals to eat mushrooms.

So with good coordination, and a few smart minds, there is a possibility to survive. Maybe the cows can survive off mushrooms too, with some insects for protein, then we can still have steak!