Fast-spreading Xylella fastidiosa is devastating species from citrus to oak trees, but can now be detected from the air.
A devastating and fast-spreading infection killing olive trees and grapevines around the world can now be detected from the air, long before symptoms are visible to the human eye.
The new technique offers hope in the battle against one of the world’s most dangerous plant pathogens, which can infect some 350 different species, including citrus and almond trees, as well as oaks, elms and sycamores. Special “hyperspectral” cameras provide an early warning system by detecting subtle changes in leaf colour.
The bacterium Xylella fastidiosa has long damaged crops in the Americas but was detected in Italy in 2013 and has now spread to France and, in 2017, Spain. It has also been found in Iran and Taiwan.
“We saw enormous devastation of the olive orchards in southern Italy,” said Pablo Zarco-Tejada, at the European commission’s joint research centre in Ispra, Italy, who led the new research. Many groves have been there for centuries and some trees are 1,000 years old, he said.
“It is spreading globally, so the alarms are [ringing] because of this threat,” he said, adding that the new technology can provide a vital tool. “It is critical for eradication, but it will not solve it totally.” The disease is being spread by the global trade in plants and this must also be addressed, experts say.
There is no cure for the disease, which in olive trees causes branches and twigs to wither and leaves to appear scorched. Culling trees is the only way to halt an outbreak, but the trees can show no visible symptoms for up to a year after being infected. During that time, a wide range of sap-sucking insects can spreading the disease.
The new research, published in the journal Nature Plants, demonstrates the first way to spot infected trees months before signs are visible to farmers. The scientists analysed more than 7,000 olive trees in 15 Italian groves over two years, both tree-by-tree on the ground and from the air.
The hyperspectral camera, flown 500 metres over the groves, analysed 250 bands of light from visible to infrared, far more than the red-blue-green seen by the human eye. With a resolution of 40-60cm each tree could be assessed for the damage the infection causes to photosynthesis and to transpiration, which is how plants draw water up to their leaves.
The researchers used artificial intelligence programs to detect subtle shifts in colour caused by changes in the pigments that the plants use for photosynthesis, such as chlorophyll. Changes in transpiration were detected by changes in the thermal infrared data – plants that transpire less get hotter. More