Instead of one specific diagnostic test for every unique bacteria, virus, fungus or nematode, it has recently become possible to detect dozens of different pathogens on plant material at the same time. One of these multiplex detection technologies is the Luminex system. “We now have over one hundred different types of miniscule beads available, each of which can detect their own pathogen from the plant material,” says Jan Bergervoet, scientist at Wageningen UR and one of the developers of the test.

Beads

At the heart of the Luminex technology are small ‘beads’ of approximately six micrometres in size. “We can attach specific antibodies to these beads that react very specifically to a protein of a sought pathogen,” Bergervoet explains. “If we don’t have any antibodies for a specific pathogen, the technology can use segments of specific DNA or RNA from the relevant pathogen. Mix a series of these beads with a little pulverised plant material and you can ‘light up’ the beads that detect their pathogen with a fluorescent substance. They are then detected by the Luminex machine, which tells you what the plant material contains… And what it doesn’t contain!”

Notorious pathogens

With over 100 beads now available, dozens of notorious pathogens can be detected at once, says Bergervoet. “We have antibodies available against multiple pathogens in tomatoes (such as the tomato mosaic virus and the tomato spotted wilt virus). And we also have specific markers that can be attached to the beads for pospiviroids (such as the potato spindle tuber viroid).”

For breeders and plant pathogen testing services

“The ‘Multiplex Luminex technology’ is not only useful for large breeders,” continues Peter Bonants, team leader Diagnostic Development. “It is of course cheaper and faster for them to check for a whole series of possible pathogens at once. But it can also be used by plant pathogen testing services, for instance, to test material for import or export in one go.”

Expansion kits for new antibodies

There are already many different ‘kits’ available and validated for various antibodies and DNA or RNA markers. “But by definition the system will be in constant development,” says Bonants. “We will continue to try and find new antibodies or DNA or RNA markers for new pathogens, and also for so-called ‘look-alikes’ which sometimes cause false results in conventional diagnostic methods. The Clavibacter bacteria in tomato breeding, for instance, has bacteria that cross-react in conventional diagnostics. This system means you can also establish or exclude these look-alikes in one go.’