Why there’ll be no blight on Mars

I’m hoping to go and see The Martian soon, one of the few films to feature a botanist as the hero. Astronaut Mark Watney is one of the first humans to set foot on Mars, but accidentally gets left behind and has to survive on his own – and to do so he grows potatoes. He wouldn’t be the first person (or even population) to rely on potatoes for survival, but here on Earth there’s a slight snag. The potato (Solanum tuberosum) has an arch nemesis – late blight, caused by an organism called Phytophthora infestans. It cuts down both potatoes and tomatoes, and was the biological cause of the Irish Potato Famine in the 19th century.

P. infestans is an oomycete, an organism that used to be categorised as a fungus, but is now considered to be a separate class of life. It can travel on the wind, and overwinter in potato tubers in the ground. It won’t arrive on Mars because, as a planet that could be host to its own forms of life (and where we’re looking for signs of life), anything that lands on the planet is subject to stringent contamination-control protocols. Everything will be cleaned to a high standard before launch, and any seed potatoes or other propagation material would have to be certified disease-free. For potatoes this may mean plants created from micropropagation (a technique that takes healthy shoot tips and grows them into plants) or grown in an indoor aeroponic system.

Late blight thrives in certain temperature and humidity conditions. In the UK, growers watch out for Smith Periods, when there are at least two consecutive days with a minimum temperature of 10° and at least 11 hours with a relative humidity is greater than 90%. That’s when non-organic growers get the fungicides out to ward off the disease. Farmers and