Genetic colouring could unlock robotic weeding

BY ANTHONY KING | 8 MAY 2024

Genetically modifying the colour of crops could help robots to pick out the weeds.

Crops could be genetically engineered with colour to distinguish them from wild and weedy relatives, plant geneticists at the University of Copenhagen, Denmark, propose. This would enable weeding robots to combine a camera with AI to learn how to identify and destroy weeds, while sparing nearby crops.

‘The solution we propose is to introduce small subtle changes through mutations. It doesn’t imply we will make rice blue or wheat orange,’ says Michael Palmgren in Copenhagen, who led the proposal (Trends in Plant Science, DOI: 10.1016/j.tplants.2024.03.001). ‘Maybe you cannot see [the difference] with your eyes.’

One strategy could be to increase pigments present in crops such as anthocyanins or carotenoids, which make blueberries blue and carrots orange. But it could also involve a change of leaf shape or hairs on the stem.

Today, the major crops of rice, wheat, corn and barley are annual grasses and must be sown, protected as seedlings and harvested entirely within a year. Cultivation often requires tilling and ploughing and spraying with fertiliser and pesticides.

The group in Copenhagen is on a mission to turn perennial grasses such as intermediate wheatgrass (Thinopyrum intermedium) and the barley relative Hordeum bulbosum into profitable crops. ‘We think perennial cereals would be a solution to more sustainable agriculture in the future as they use less inputs and less machinery and they will store CO₂ underground,’ says Palmgren.

Once a wild plant is domesticated, its relatives can invade a crop field as weeds. ‘Our crop plants use energy to make food. Weeds don’t have that issue, so they grow better,’ says Palmgren.

The idea of tweaking the newly domesticated crop plant stemmed from this problem of weed relatives and the desire to avoid herbicide spraying. The group plans to screen for mutants to find suitable plants for this approach to distinguish crops from weeds.

‘This is an interesting new idea,’ says Dana MacGregor, a plant geneticist at Rothamsted Research who studies the genetics of weeds to understand how they outcompete crops. She notes that ‘many of the suggestions concern changing a single gene and it is easy enough for weeds to overcome a single gene trait’.

Some of her research has shown that weeds can evolve to look more like a crop. ‘Weeds are ingenious because they are fighting for their lives. Any plant that survives creates a seed bank and those traits get rapidly introduced in any agricultural system’ says MacGregor.

One way to make the approach more powerful could be to ‘select for multiple traits,’ such as purple and round leaves, which would make it more challenging for weeds to match the crop.