SOMETIME in the next decade NASA plans to collect a sample of Martian soil and bring it back to Earth. In anticipation, the US National Research Council has pointed out that if there are microscopic life forms on Mars, they could be dangerous. However remote the risk, samples should be delivered straight to a biosafety level-4 lab, the sort where deadly viruses such as Ebola are handled. By the same token, we have a moral duty not to infect other worlds, so vast amounts of time and money are going into making sure that Mars missions do not export potentially deadly micro-organisms from Earth.
Unfortunately, these wholly sensible interplanetary precautions have not been adopted closer to home. Here on Earth, many inhabitants are facing the very real prospect of annihilation by alien pathogens. The cavalier way we move millions of plants from one continent to another shows scant regard for the health of forests and other ecosystems. History has shown that importing exotic pathogens to places where plants have no resistance to them can spell disaster.
Today鈥檚 disaster in the making is sudden oak death, a disease caused by a fungus called Phytophthora ramorum. Native to Asia, this micro-organism slipped into the US and Europe on ornamental plants. In California, the disease had become epidemic in wild woodlands before anyone knew the fungus existed. Now it is killing trees in the UK and the Netherlands. If efforts to contain the infection fail, it could do untold damage to forests worldwide. Even if we are lucky this time and the epidemic fizzles out, celebrations are likely to be short. Other potentially devastating phytophthoras are almost certainly on the way (see 鈥淔elled by fungus鈥�).
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If we are prepared to go to great lengths to avoid an invasion of Martian microbes, why aren鈥檛 we making more effort to curb the spread of terrestrial pathogens into alien territory? Almost every serious epidemic of plant disease, from potato blight to Dutch elm disease and now sudden oak death, was the result of moving infected plants or timber around the world. We know from bitter experience that bringing species together that would not normally meet can be disastrous 鈥� diseases such as SARS, bird flu and HIV all emerged this way. Species that have evolved together tend to achieve a balance: left in their natural habitat, most plant pathogens cause mild diseases in their hosts. But let them loose among strange species and they can turn into serial killers.
In the world of emerging plant diseases, the main risk comes from the plant trade. In many developed nations, gardening itself has grown to epidemic proportions, and countries as far apart as China and South Africa, New Zealand and the Netherlands have established vast industries to feed the demand for exotic plants. Though safeguards are in place aimed at preventing pathogens arriving with the plants, it is clear that they do not work. The main reason for their failure is that most potentially dangerous plant pathogens are still unknown to science and so don鈥檛 feature on any quarantine schedule. They only make the list once they have revealed themselves, and that might be by felling foreign forests or ravaging crops.
So what鈥檚 the answer? There has to be a better solution than chopping down and burning trees, and destroying the entire stock 鈥� and livelihoods 鈥� of nurseries that have inadvertently brought in the infection. If exporting nations are to continue to sell plants in bulk, they need to guarantee that those plants pose no threat. That means making an effort to find out exactly what lurks on the plants and in their pots, and introducing effective screening methods.
If exporters are unwilling to do this, they might find the alternative even less palatable. The simplest way to prevent new epidemics is to stop the mass transport of plants altogether. That doesn鈥檛 mean forcing gardeners to shun exotics in favour of native plants 鈥� although that might be no bad thing. But it does mean big changes in the horticulture industry. Retailers who buy in bulk from foreign suppliers would have to switch to locally produced plants, grown from 鈥渃lean material鈥�, perhaps propagated from seeds or cell cultures, or from small numbers of quarantined plants. Prices would inevitably soar. But what price our native ecosystems?