PLANT BREEDING
Resistance at the cost of growth
Agricultural plants have been bred for maximum yield, which means they invest less in defending themselves.
Here, an ear of rye has been infested with the ergot fungus, which is poisonous to both humans and animals. | Photo: Ernst Weingartner/Keystone
Plants face a specific challenge. They have to defend themselves against pathogens, but at the same time weigh up how much energy to invest in this without unduly reducing their growth. Anna-Liisa Laine from the University of Helsinki (previously of the University of Zurich) is one of a group of researchers who have been analysing data on almost 200 plant species in order to determine whether different species adopt different approaches to this dilemma of resistance versus growth.
They used a group of resistance genes that can be found relatively easily in the genome, and that can serve as an indicator of how much a plant species is investing in defending itself. “We divided up the species into cultivated and wild plants”, says Laine. “This is because humans have bred crop plants specifically to deliver a high yield to such an extent that we had to expect different results”. Their analysis showed that this trade-off is indeed to be found in wild plants – in other words, the more they invest in defence, the less they grow. But they found no such correlation in the cultivated plants.
One reason for this is the lack of resistance genes in crop plants. Many genes were lost unintentionally because these plants were bred always for maximum yield, not for their qualities of resistance. “In contrast to agricultural species, their wild relatives have a much bigger repertoire of resistance genes”, says Laine. “This is something that could be put to use in future breeding programmes”. Such programmes are necessary because crop plants, being less resistant, can only grow thanks to an abundant use of fungicides and other pesticides. And that isn’t compatible with more sustainable agriculture.
In order to optimise cross-breeding between crop plants and their wild relatives, it’s important that we investigate their defence mechanisms in greater detail. It’s possible that a few specifically selected resistance genes might be more efficient than thousands of others. An optimised crop plant variety would have exactly the right number of resistance genes to enable it to continue its heavy investment in growth.
