- Author: Ben Faber
PULLMAN, Wash. Soil pathogen testing - critical to farming, but painstakingly slow and expensive - will soon be done accurately, quickly, inexpensively and onsite, thanks to research that Washington State University scientists plant pathologists are sharing.
As the name implies, these tests detect disease-causing pathogens in the soil that can severely devastate crops.
Until now, the tests have required large, expensive equipment or lab tests that take weeks.
The soil pathogen analysis process is based on polymerase chain reaction (PCR) tests that are very specific and sensitive and only possible in a laboratory.
The new methods, designed by WSU plant pathologists, are not only portable and fast, but utilize testing materials easily available to the public. A paper by the researchers lists all the equipment and materials required to construct the device, plus instructions on how to put it all together and conduct soil tests.
Responding to growers needs
"We've heard from many growers that the time it takes to obtain results from soil samples sent to a lab is too long," said Kiwamu Tanaka, assistant professor in WSU's Department of Plant Pathology. "The results come back too late to be helpful. But if they can get results on site, they could make informed decisions about treatments or management changes before they even plant their crop."
Some diseases from soil pathogens may not be visible until weeks after the crop has sprouted, Tanaka said. That could be too late to treat the disease or could force farmers to use more treatments.
WSU graduate student Joseph DeShields, a first author on the paper, said it took about six months of work to get their device to work in the field. It relies on magnets to capture pathogens' DNA from the soil.
"It turns out, it's really hard to separate and purify genetic material from soil because soil contains so much material for PCR tests," said DeShields "So we were thrilled when we made that breakthrough."
Rachel Bomberger is a WSU plant diagnostician who helped with the concepts of the machine testing. She said she's impressed by what Tanaka and the team accomplished.
"We removed a huge stumbling block when it comes to soil testing," said Bomberger, one of the co-authors on the paper. "We found the missing piece that makes the testing systems work in the field without expensive lab equipment or testing materials."
The system was tested on potato fields around eastern Washington, Tanaka said, but it will work on soil anywhere in the world.
"It's a really versatile method," he said. "You could use it for nationwide pathogen mapping or look at the distribution of pathogens around the country. We started small, but this could have huge implications for testing soil health and disease."
Tanaka said it was important for this discovery to be available in an open-access video journal.
"We're always concerned about helping every grower and the industry as a whole," Tanaka said. "We want everybody to look at this and use it, if they think they'll benefit from it."
The results were published in the Journal of Visualized Experiments, an open-access journal that includes a video showing how to assemble and used the system and a full list of materials needed to use their method.
This research is supported by the Northwest Potato Research Consortium and the Washington State Department of Agriculture - Specialty Crop Block Grant Program.
See the video here:
And the article here:
- Author: Ben Faber
The disease pyramid describes how disease can eventually destroy a plant.
It is comprised of the presents of the pathogen that causes the disease, the plant or host, the environmental conditions that sets up the pathogen to go after the plant and time. It requires all four at the same time to have a disease. So in the case of avocado root rot, it's necessary to have Phytophthora cinnamomi there with a susceptible avocado root, in warm, moist conditions for a period of time for the disease to express itself. For a young tree, the disease may show up within a year but for older trees it may take several years to see the disease symptoms. For avocado crown rot, it may take several years for Phytophthora citricola to appear. In the case of Huanglongbing, not only is the pathogen required, but also the vector for spreading it, the Asian Citrus Psyllid. At this point in California, we have a rapidly spreading vector, but as yet, it appears the psyllid is not infected with the bacteria causing the citrus disease.
Not only time is important, but timing of sampling and point of sampling are important. In the case of avocado root rot, the best sample if from a recently infected root in the spring or summer. A thoroughly destroyed root taken in the winter will often give a negative response. The pathogen has done its ravages and is no longer active. If the wrong leaf or root is sampled for the Huanglongbing bacteria, the assay will show a negative response, even though it is in the plant. (This may have something to do with Einstein's Theory of Relativity in this 100th year of pronouncement, but I doubt it).
And then too, even if a disease is finally diagnosed, it doesn't mean the tree is going to die. If Phytophthora is caught soon enough, it can be treated with phosphites, but the environment needs to be changed at the same time. Meaning, the irrigation needs to be adjusted so that the treatment will work. If the irrigation is changed, the trunk canker will disappear.
It also means that all those terrible disease out there that threatened our trees in other countries won't hurt ours. We have a different environment from Thailand, India, Brazil, etc. and so even though there may be devastating disease there, since we don't have the environment, we wont get those diseases. Yeah, we are going to get huanglongbing and polyphagous shot hole borer fusarium, but we should be happy we aren't getting all the other problems other countries have. This is a way of saying, happy New Year. It could be a whole lot worse and we are doing pretty well.