growing potatoes on Mars, without blight
Astronaut Mark Watney grows potatoes to survive on Mars, in ‘The Martian’
(Image credit: 20th Century Fox)

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.

Blighted potatoes

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 gardeners alike can sign up for BlightWatch, a notification system that lets them know if these weather conditions have occurred in their area. Settlers on Mars wouldn’t have to worry about the weather, as they’ll have to provide a controlled environment in which to grow their crops. They can adjust the controls accordingly!

Whilst this may seem like a flight of fancy, NASA’s discovery of flowing water on Mars brings us one step closer to being able to grow crops there one day – it means there’s one less thing for a crewed mission to pack 😉 Growing crops on a planet is already easier than growing them in space, because they’re used to the presence of gravity, even if it’s less than on Earth. Radiation will be an issue….

One of the main problems for Earth-bound gardeners is that the disease mutates – it evolves. Although it is possible to develop potato varieties with blight resistance (whether by conventional means or GM technology), that resistance doesn’t last. At some point blight will overcome it.

So how do gardeners on our little blue planet avoid late blight and get the best possible crops of potatoes and tomatoes?

  • One of the most important considerations is to choose your varieties wisely. There are potato and tomato varieties with current late blight resistance (look for Sárpo potatoes and Crimson Crush tomatoes, for example). Failing that, consider early varieties that will crop before the main late blight season.
  • Buy certified seed potatoes or microplants, rather than planting anything left over from your grocery shopping. Late blight can and does overwinter in potatoes.
  • Likewise, keep things clean. Make sure you remove any plant foliage and tubers at the end of the year. If you have infected plant material, don’t add it to your compost heap – send it for commercial composting (which should kill the pathogen) or put it in the bin. If ‘volunteer’ potato plants come up in spring, remove them before they have a chance to spread blight. They’re not ‘free plants’, they’re a poisoned chalice.
  • Earth-up your potatoes (the further down they are, the longer the pathogen will take to get to the tubers) and keep the foliage dry (water the soil, not the plants, when necessary).
  • Indoor crops of tomatoes are less likely to fall prey to late blight – but they are not immune, especially if the indoor conditions match the Smith Period criteria.
  • Practice a crop rotation – you should leave at least 2 years between planting potato crops in the same area, preferably 3 or more.

Tomato blight

Whilst the general consensus is that tomatoes and potatoes from plants affected by blight are safe to eat (humans not being susceptible to plant diseases), it’s worth noting that the USDA recommends that affected tomatoes are not used for canning – apparently the tissue damage and rise in pH the pathogen causes means the canned tomatoes would not be safe from developing other disease organisms that would be harmful to humans.

You can save seeds from affected tomatoes as the pathogen can only survive in living tissue – once the seeds have been cleaned and dried, it will die.

Further reading:
More on Oomycete, from Wikipedia.

Production of disease-free seed potatoes, from the FAO.

Tomatoes and Potatoes Infected with Late Blight – Are They Safe for Canning?

What’s Safe to do with Potatoes and Tomatoes that had Late Blight?

Moving beyond potatoes for more calories in a small space

If you’re looking for blight-resistant seeds for next year, T&M are one possible source of Sárpo seed potatoes – you may also find them in your local garden centre (and if you can’t – ask them to stock them!). They’re developed by the Sávári Trust, who are also behind the Crimson Crush blight-resistant tomatoes available from Suttons. You can now buy seeds (new this season) and there will be plants available next spring. Victoriana Nursery Gardens also offer blight-resistant tomato varieties as seeds and plants – look for ‘Clou’, ‘Primabella’ and ‘Primavera’.