快猫短视频

EVEN when you see it from an aeroplane, the sheer scale of farming in the
heartland of North America is hard to comprehend. Each one of those squares or
circles in the endless patchwork of maize and wheat, soya and alfalfa that rolls
from horizon to horizon can measure a square mile鈥攁bout 260 hectares, the
standard unit for field sizes in this part of the world. Farmers rarely stroll
through fields that big. They might send in a sprayer every few weeks, and
finally a harvester. Otherwise, plants on which millions depend for food are on
their own.

Let us imagine, then, that from your plane you see a small cloud of something
emitted from a pickup truck on one of the deserted access roads. You are the
only person who saw it. No one notices that the crops have a new infection until
harvest. Then the farmer may keep it quiet to protect the value of his crop, or
perhaps the infection shows itself only when the crop is eaten, or when next
year鈥檚 seeds are planted. Choose your scenario.

Suppose it was a wheat field and the cloud was spores of a wheat smut. The
fungus has little impact on the harvest because US wheat is bred to resist it.
But the disease is on the exclusion list of every wheat-importing country in the
world. The US loses a billion dollars in exports, there is economic ruin in the
wheat belt, world grain prices rise and hunger and unrest stalk some Third World
cities.

There again, perhaps it was a maize field, and the cloud was millions of
whiteflies carrying a usually harmless maize virus that has been genetically
engineered to make botulinum toxin. The toxin turns up in beer made partly with
maize, and sickens some people. Next year, more maize is affected as local
whiteflies acquire and spread the virus. Another food scare. Another
government鈥檚 credibility in tatters. The US launches a billion-dollar whitefly
control programme and burns thousands of hectares of farm land.

Or it could have been a soya bean field, and the cloud was an aerosol of
Pseudomonas tabaci鈥攁 bacterium that produces deadly tab toxin.
Relatively few fields are affected, but soy is used throughout the food
industry. The contaminated batch kills some cattle, then a few people. Too small
an outbreak to count as a major threat to public health, but enough to fuel a
massive food scare. US soya exports grind to a halt. World fodder and meat
prices skyrocket.

Killing fields

Improbable scare stories? That depends on who you ask. Crop bioterrorism may
not have made it on to the agenda in Europe, but a growing band of plant
pathologists and defence analysts in North America claim that if your aim is to
wreak economic damage, destabilise governments, or simply get a business
advantage, there are few easier targets than those lonely waves of grain. No one
is claiming that such attacks have already happened鈥攁lthough that has not
been ruled out. But at a symposium on anti-crop bioweapons at the Joint American
and Canadian Phytopathological Society meeting in Montreal in August, they
argued that measures must be taken now to stop bioterrorist strikes against
crops becoming inevitable.

Crop diseases are not a new temptation. By the time the US renounced
biowarfare in 1968, it had stockpiled 30 000 tonnes of wheat stem rust spores to
drop on the Soviet Union, and a tonne of rice blast for Asia. The Soviet Union
stockpiled wheat stem rust, and pathogens of maize and rice. Iraq had a wheat
smut bomb.

But what has changed is the objective of crop biowarfare and the ease with
which a 鈥渂iobomb鈥� might be deployed. The military motive has traditionally been
to deprive an enemy of food during wartime, says Mark Wheelis of the University
of California at Davis, who studies bioweapons for the Federation of American
快猫短视频s in Washington DC. This goal was so difficult to achieve, he says,
that it helped convince the US to abandon crop weapons research when it did.
Terrorists, on the other hand, don鈥檛 need to annihilate the whole harvest to
disrupt trade or discredit authorities. If that鈥檚 the goal, a little plant
disease鈥攐r the rumour of it鈥攇oes a long way.

Even in rich countries the average city has only enough food to last five
days, writes Wallace Deen, a consultant formerly with the US biological defence
programme, in a report published in November in the Annals of the New York
Academy of Sciences. In poor countries, a slight reduction in harvest can
raise staple food prices for the urban poor enough to spark civil disturbance.
Witness Indonesia after the Asian financial crisis in late 1997鈥攔elatively
small price rises for rice fuelled food riots in major cities around the
country.

Health scares might be a better way to destabilise governments in the wealthy
West. At the Montreal symposium, 鈥渆veryone thought it significant that it only
took a little bit of dioxin in Belgium last summer to create a food scare, ruin
the livestock industry, destroy food exports and bring down the government,鈥�
says Norm Schaad, of the Foreign Disease and Weed Science Unit in Fort Detrick,
Maryland, part of the US Department of Agriculture (USDA). 鈥淎 terrorist might do
the same with only a small outbreak of the right crop disease.鈥�

Political or ideological enemies needn鈥檛 be the only targets鈥攔ivals for
export markets may also be tempting. China, a major maize exporter, would
benefit if disease blighted US maize, and vice versa. Even corporations could
get in on the act. 鈥淪ay one company grows pineapples in countries where
production is limited by a pathogen, which does not occur in countries where a
rival operates. The first company might even out this trade advantage by
spreading the pathogen,鈥� says Wheelis.

鈥淭he globalisation of trade is the most important development for those who
would use biological weapons against plants,鈥� says Deen. Bioterrorists can cause
havoc, he says, by contaminating just a fraction of a crop鈥攊nternational
trade restrictions will do the rest.

Under the World Trade Organization鈥檚 鈥減hytosanitary鈥� rules, a minor disease
outbreak can take an entire crop off the export market. Take karnal bunt, a
relatively mild鈥攊f highly infectious鈥攚heat smut that turns grain
black, sticky and inedible. When the smut blew into Arizona from Mexico two
years ago, 32 countries, including China, banned US wheat imports in one day.
The US spent hundreds of millions of dollars to eradicate the fungus and save
its $5 billion annual wheat exports. This episode helped to fuel current
US fears of anti-crop weapons, as it dawned on plant pathologists that a
deliberate attempt to sabotage US grain exports might not look very
different.

So much for motives, but what about means? Building a biobomb aimed at plants
would be a far less ambitious undertaking than designing one to take out humans
(鈥淎ll fall down,鈥� 快猫短视频, 11 May 1996, p 32).
A large-scale biological attack on people needs a carefully 鈥渨eaponised鈥� germ, to ensure that
pathogens normally spread by close physical contact can be transmitted through
the air and still be infectious. Plant viruses, bacteria and fungi, on the other
hand, are already adept at seeking out and destroying victims that don鈥檛 move.
They are conveniently adapted to be spread by the wind and insect vectors.

And although genetically engineered crop bioweapons may sound scary, there鈥檚
little need for them. 鈥淵ou can always find a natural plant pathogen as nasty as
anything you could create,鈥� says Anne Vidaver, head of the Center for
Biotechnology at the University of Nebraska, Lincoln. One exception might be an
otherwise benign virus engineered to produce a human toxin鈥攈armless for
the plant, but a nasty surprise for whoever eats it.

Naturally occurring fungi such as smuts and rusts are far more likely to be a
crop bioterrorist鈥檚 weapon of choice, says Vidaver. Fungal spores are tough, and
can infect crops in a wider range of growth stages and environmental conditions
than most bacteria and viruses. Fungi can also produce potent toxins, so even a
small infestation can make an entire harvest toxic.

Pathogens for plant bioterrorism are a lot less trouble to breed than those
aimed at humans because they need not be highly specific to the target, or even
destroy that much of a crop to have an impact. Just a small greenhouse full of
the crop and a few pathogens collected from local crops鈥攚hich are likely
to be different from those to which the crops in your target country are
immune鈥攚ould suffice. A plant biological weapon would even be safer to
manufacture than one designed to attack humans, which can always turn on its
creators.

All the same, preparing a crop biobomb would not be a trivial undertaking.
For instance, the spores would have to be specially formulated to prevent
clumping, and to protect them from ultraviolet light. But with a little luck and
a little technical expertise, a weapon could be cooked up in someone鈥檚
backyard.

They could even get away with it. Spray anthrax from a light aircraft over
bustling Washington DC and someone is going to notice. Spread spores of karnal
bunt over the lonely plains of Kansas and in all likelihood nobody will see.
Agriculture may be the world鈥檚 biggest industry, and the most vital for human
well-being, but it is also one of the least secure. 鈥淵ou could do enough damage
to achieve your goal just by bringing in a suitcase full of vials of the
pathogen and strolling past a field with an atomiser,鈥� says Wheelis.

Soft target

What鈥檚 more, natural outbreaks of novel plant diseases have multiplied
dramatically over the past decade as food, seed and people cross borders at
ever-increasing rates. In North America, 25 plant viruses alone are listed as
new or re-emerging, while the European and Mediterranean Plant Protection
Organization in Paris has an 鈥渁lert list鈥� of 31 fungi, bacteria and viruses that
are threatening to invade Europe. 鈥淲ith all these novel infections happening
naturally,鈥� says Vidaver, 鈥渋t may not be obvious if an outbreak is
诲别濒颈产别谤补迟别.鈥�

One way to deter would-be bioterrorists is to deny them deniability. 鈥淚f we
could say where a pathogen comes from, we could narrow things down,鈥� says
Schaad. To that end, his unit at the USDA has collected thousands of plant
bacteria from around the world. The next step is to DNA fingerprint the bacteria
so that when a suspicious outbreak occurs, plant pathologists will quickly be
able to work out where the errant pathogen came from. There are no libraries for
fungal and viral pathogens. 鈥淲e spends millions collecting genetic varieties of
crops, but nothing on collecting their pathogens,鈥� says Schaad.

In September, President Bill Clinton announced that $215 million would
be spent to upgrade a USDA agricultural quarantine laboratory on Plum Island off
the coast of New York State, to deal with threats to US agriculture, including
plant pathogens. The lab will be equipped to analyse pathogens sent in from any
suspicious outbreak. Assuming, of course, that someone notices such an outbreak
in the first place. Farmers are not obliged to notify the authorities when an
outbreak occurs. An attack 鈥渃ould occur without us knowing it, because we really
don鈥檛 have the tools in place to detect [it]鈥�, Floyd Horn, head of the USDA鈥檚
research service, told the US Senate last month.

鈥淲e need automated systems that will enable people to get immediate
identification of pathogens in the field,鈥� says Schaad. Such systems would rely
on DNA and protein analyses similar to those being developed to detect
biological weapons aimed at people
(鈥淏ioarmageddon鈥�, 快猫短视频, 19 September 1998, p 42).

No amount of technology will help, of course, if there are not enough plant
pathologists to police the crops. Even as the threat of natural and unnatural
disease outbreaks increases, says Bob Forster of the University of Idaho in
Kimberley, there is a declining number of people who can identify diseases in
the field.

Assuming you have identified a crop bioterrorist attack, how do you limit the
damage? Fungicides can stop or slow the spread of a fungal disease. But for
crops infected with bacteria or viruses, usually the only option is to burn
them, and eradicate any insect vectors, which can be extremely difficult and
costly.

An alternative approach would be to rapidly replace contaminated crops with
those that are resistant to the pathogen. Plant breeding companies are investing
millions characterising plant genes. In a few years, when a new disease strikes,
it may well be possible to pull out the right resistance gene and breed it into
the crop that is under attack. The USDA has already identified 26 genes that
protect against the barley stripe rust that was wiping out the crop in the
northwest of the US in 1995. But it takes resources and time to breed new
characteristics into crops and get them out to the farms, so this line of
defence will only be available to the wealthy West, and at best can only reduce
long-term damage. Consumer opposition to genetically modified crops could also
make this approach uneconomical.

Nor is there any guarantee that there will always be a resistance gene
available. Take wheat streak mosaic, a virus that is spreading in North America
and can cause catastrophic crop losses. Despite extensive research, no one has
ever found a resistant variety. Alternative strategies do exist鈥攕uch as
using genes from other species鈥攂ut ultimately any attempt to engineer
resistance into plants only works until bioterrorists find a new pathogen. With
such strike and counter-strike, 鈥渢he world could get itself into a bioweapons
arms race鈥�, warns Brian Halweil of the Worldwatch Institute, an agricultural and
environmental think tank in Washington DC.

According to Vidaver, the best strategy is to reduce the threat of crop
bioterrorism in the first place. This goal, she says, can be achieved in part
through limiting the spread of infections by abandoning the uniformity of modern
farm fields in favour of diverse plant varieties and more crop rotation. Modern
American farms, with their huge expanses of one variety of wheat, maize or
alfalfa, are 鈥渁 disaster waiting to happen鈥�, she warns.

With the ever-increasing threat of natural plant diseases, investing in
improved vaccines and disease diagnosis, and a move away from monocultures could
start to make good economic sense. The irony will be if North American fears of
crop bioterrorism force its farmers to adopt methods that coincidentally give it
more of an edge over its global competitors鈥攅ven if the terrorists never
strike.