A 'Blood Test' for Potatoes

Identifying how much nitrogen is in a plant could answer the “How much do I need?” question.

Published online: Mar 21, 2018 Articles Rosalie Tennison
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A simple blood test at a medical laboratory can tell your doctor a lot about your health. From the test results, a doctor can suggest ways to improve your overall well-being. Human blood tests were the inspiration for Agriculture and Agri-Food Canada (AAFC) researcher Dr. Helen Tai to consider a test for nitrogen levels in potatoes. She wondered if a test could be developed that would tell potato growers if the amount of nitrogen in their plants is in the right range for a “healthy” plant. She took the idea to Dr. Bernie Zebarth, a soil scientist at AAFC, and the two Fredericton researchers began a collaboration that has resulted in a test. Now, they just have to make it accessible for plant “doctors.”

“Nitrogen is the most important nutrient for potato production from an economic point of view because an adequate nitrogen supply is needed to achieve high tuber yield,” Zebarth explains. “But, with rising fertilizer costs and possible environmental impacts as well, growers want to be smart about their nitrogen management.” With that in mind, the researchers developed what may turn out to be a smarter way of determining nitrogen levels in a plant that improves upon petiole analysis.

“Growers want to provide just as much nitrogen as the plant needs – no more, no less,” he continues. “Now, nitrogen is put on early and then a petiole analysis is taken and more nitrogen is added, if needed. But, ours is a new approach. We are looking at gene expression, which is more like going to the source. We are asking the plant if it is short of nitrogen.”
The researchers were fortunate to identify an ammonium transport gene and they are now perfecting a test that will, like a human blood test, identify if the plant is low in nutrition. The fact that Tai and Zebarth have found a gene that expresses nitrogen status in potatoes is more astounding when it is understood they have identified something that is unique in the world, as no other test based on gene expression has been developed for nutrient management of any crop.

“Although other researchers have been working on screening genes, which may be used to test for nitrogen in rice and corn, we are the first to have a field-validated gene expression indicator,” comments Tai. 
The process is simple – a standard one-hole punch is used to extract a number of small discs of plant tissue from a leaf and then it is frozen to preserve the RNA. Once at the laboratory, the sample is reduced to its genetic components and analyzed. If the plant is low in nitrogen, the gene shows greater activity to get the plant to produce the proteins needed to get more nitrogen. If the plant has the nitrogen it needs, the gene is less active. The researchers are now perfecting the test to see if it is valid across potato varieties, fertilizer nitrogen sources and different timing of spring fertilizer applications.

“We did a greenhouse test comparing nitrogen sources and the gene was not affected, so the test only indicates the plant is lacking nitrogen and not what the source of the nutrient is,” Zebarth explains. At this point, the test cannot indicate how much nitrogen would need to be added to ensure the health of the plant, but it is still “early days” for this research.
The researchers are not limiting their research to nitrogen because the economic feasibility is not there, so they are working on a combination approach. “If we were just interested in nitrogen, it wouldn’t make sense,” Zebarth admits. But, the team believes the test could be used to measure a number of plant stresses, from nitrogen deficiency to drought stress to potassium and phosphate shortages. They have been focusing on nitrogen because there is no definitive test for nitrogen in Eastern Canada and the soil tests used in Western Canada are not always accurate.

Zebarth believes they might have an on-farm test perfected in about five years, so growers could work with a crop consultant to take samples and deliver them to a laboratory for analysis. Before that can happen, the method needs to be honed from determining when to take a sample to understanding how the results are interpreted. The researchers’ understanding of how gene expression can be used to assist potato growers produce their crops more efficiently and economically is only the first step. The fact that they have already identified the gene is making Tai’s idea of creating a blood test for plants closer to a reality.