Can we make plants grow in salty soil?
Too much salt in your diet can be risky for your health, and the same also goes for plants. But as the human population increases, and the amount of land available for farming drops owing to the effects of climate change, finding salt-free soils, and salt-free water for growing food, will be problematic. Chris Smith went to see two plant scientists, Sandra Schmoeckel and Mark Tester, at the King Abdullah University of Science and Technology (KAUST) in Saudi Arabia. They're looking at a South American plant which can tolerate large amounts of salt, to see how it does it...
Sandra - In front of you in the little cup you can see quinoa seeds. So quinoa's quite interesting; it's sort of cooks like rice; tastes a little bit nuttier. The interesting thing is that it has more protein than other cereals like rice or wheat that you would eat. It's gluten free and it has a really interesting composition of proteins because it contains lots of essential amino acids.
Chris - And so why are you interested in this?
Sandra - We are mainly interested in it because it's extremely salinity tolerant. So, if you water it with half sea water, you still get two thirds of its yield.
Chris - And Mark - we're not accustomed to growing plants irrigated with seawater so why is this even a consideration?
Mark - The world's running out of water. About 40% of our world's food is grown under irrigation and a large fraction of that is exploiting groundwater resources that are being depleted. It's an unsustainable extraction, we can't keep going the way we are. We both have to be able to use the lower quality water that we have got left and we need to start considering opening up new water sources, and the obvious source is seawater.
Chris - That means you either got to now find plants that like growing in seawater or what, change the plants so they can tolerate seawater?
Mark - Or a bit of both. So what we need to be able to do is make plants more salt tolerant so they can be irrigated with salty water. So what we need to be able to do is partially desalinise the seawater, increase the tolerance of some of our crops, then we might be able to develop a whole new agricultural system based, ultimately, on seawater.
Chris - And Sandra - how are you approaching that? What are the steps that you're taking to try and turn this quinoa from something that will grow in saltyish soil in South America into something that could be a viable agricultural product?
Sandra - There are lots of quinoa varieties. Not all of them are really useful at the moment for farmers because they have different heights, they have different colours, they're very various. So there still has to be lots of breeding to fit the economic traits that the farmers would like to scale it up to industrial scale. The other really big problem we have is these quinoa seeds have bitter compounds on them which we call saponins. They are soapy molecules that have to be removed with lots of water and...
Chris - Do you know why they're there?
Sandra - Yes. We don't have experimental evidence for it as such but it has been observed that in fields where you have quinoa growing with lots of saponin, you have less birds feeding on the quinoa seeds.
Chris - So it's a bird deterrent but, because it's bitter, it's also a human deterrent and you'd like to get rid of it?
Sandra - Exactly! So the humans don't like the bitter taste of the quinoa seeds so it has to be washed off before it's useful for human consumption.
Chris - How do you propose to do this then? How are you going to get versions of this plant that don't make those seeds with those compounds in them?
Sandra - There are some varieties of quinoa that contain few saponins but these are not really useful for any industrial use at the moment. So we have looked at a quinoa variety in real detail, so we've taken the genome, and we're sequencing the genome, and looking in really great detail. And we also, because we know some of the lines that contain few saponins, we can breed that together with the lines that contain high saponins, and then we go down a few generations. And then, based on Mendel's laws we know that one quarter of the offspring will contain no saponins and the others will. So now we can compare the genomes because we have all the detailed information and, hopefully, we'll be able to nail down that gene that confers these saponins and is responsible for that. And, hopefully, we'll find a way, using modern technologies, to reduce that amount of saponins or we can just breed the sweet line with commercial lines and look for that marker of sweet, so low saponins, and then continue the breeding and make the plant sweet.
Chris - How realisable is this?
Sandra - I think we're pretty close. The genome - we have that already assembled. We are on the way. We do have the lines that I talked to you about. We have bred the sweet and the bitter lines and we have grown them. We have analysed the amount of saponins we have in there. What we now need to do is bring those two bits of information together, overlay them, and then look for the genes.
Chris - What about the salt tolerance that Sandra's mentioned, Mark? Are there other things that the genome will unlock for you and inform how this plant handles salt so well so you could put it into other plants?
Mark - That's exactly right, Chris. What we're doing is using the genome both for improving the quinoa and its agronomic properties that Sandra's just described and, also, learning from the genome and from quinoa. It really is an amazing plant - very salt tolerant. Really, the main thing is to learn how it's so salt tolerant and then transfer that knowledge into other crops, which are currently established, but more salt sensitive. The extreme example being rice, which feeds half the planet, but is very salt sensitive. What's particularly remarkable about the plant is the leaves taste salty. They've got a lot of salt up in those leaves. How does a plant tolerate that? How does that plant keep green, and keep photosynthesising, producing sugar, growing grain? That is remarkable and I'd love to learn that because plants like rice and wheat are pathetic at that.