Root architecture discoveries could help breed drought-resistant crops

We should breed new varieties of crops based on their root architecture rather than just focusing on the top half of the plant, according to scientists looking at how to cultivate plants that use water more efficiently and better withstand drought conditions.

Yellow, parched fields were a common sight in Europe this summer. The severe 2018 drought caused damage to wheat, maize and barley crops, with harvests down in many EU countries. And climate scientists predict that European crops will suffer from more frequent and extreme heat in the coming years.

The most visible signs of heat stress and water shortages are seen in leaves, but plant scientists have begun looking for solutions in ‘the hidden half’ – the roots. 

‘You could argue that for the last 10,000 years, we have selected crop varieties on the basis of the upper half, and not focused on this hidden part of crops,’ said Malcolm Bennett, professor of plant science at the University of Nottingham, UK. ‘If we could select new crop varieties based on root architecture, we could significantly improve their ability to forage for water.’ 

Roots absorb water and nutrients from soil and store food for the plant. Deeper rooting cereal crops could suck up water from further underground, or dense shallow roots might better capture nutrients like phosphorus that gather at the surface.

Plants can have a similar biomass of roots to the part that is above ground – the challenge is how to see living roots in order to analyse them.

Prof. Bennett has found a solution. He now scans roots growing through soil using X-ray micro-computed tomography (micro CT), the same technology routinely used by doctors to see inside patients. His machine, though, is a colossus, three to four times bigger than a typical medical scanner and a one-of-a-kind in Europe for life sciences.

It’s so big that a new building – the Hounsfield Facility – was constructed to house the giant scanner, which is encased in 20 tonnes of lead. A heavy-lifting robot installed it onto a specially reinforced floor.  ‘Scanners (of this size) are normally used in the car and aerospace industries, where they are used to scan engine and wing parts for faults,’ Prof. Bennett explained. ‘Ours allows us (to) image living roots.’

The researchers grow wheat in one-metre high PVC plastic tubes, and then image their roots throughout their life span. Over 8,000 X-ray snaps are taken and computer algorithms stitch these sections together to create a 3-D image of roots growing in soil at a single point in time. Because plants can withstand more X-ray power than humans, the resolution is much higher and can reveal even the thinnest of root hairs. Scanning can be done repeatedly to image the growth of roots.

As seen on CT – root structures revealed by the Hounsfield scanner

The 3D-images of underground roots are publicly available on the Hidden Half website. It currently hosts scans of roots from fruit, plants, trees, cereas, vegetables, herbs, grasses and weeds. Image credit – Brian Atkinson

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