Research Highlights

Variety Trials for Iron Deficiency Chlorosis in North Dakota Help Farmers Choose Seed Wisely

By Carol Brown

In many soybean-growing states, there are teams of researchers testing varieties to see which ones offer the best performance for that area. As each state differs in seasonal growing conditions, soil type, water availability and more, one variety may perform well across several areas, or it may not. It is important for farmers to have a good idea of what to expect when planting acres of specific seeds.

Carrie Miranda, North Dakota State University assistant professor, heads up the university’s soybean breeding program. She took on this role in 2020, after the retirement of Professor Ted Helms, who established the NDSU’s soybean breeding program in 1986. Miranda is also part of the state’s annual Soybean Variety Trials, where she focuses on iron deficiency chlorosis.

“IDC is an issue in certain parts of North Dakota and yield loss due to IDC can be devastating. It’s important for farmers to know the IDC scores of varieties to ensure they are purchasing the correct variety for their land,” Miranda says. “The soybean variety trials are a long-running project, and our reputation is high because of its success. We are appreciative of the North Dakota Soybean Council, which has been funding it for years.”

As part of the trials, Miranda conducts side-by-side IDC resistance tests of approximately 200 soybean varieties from private seed companies as well as lines from her own breeding program. Soybean varieties that have resistance genes to soybean cyst nematode and other diseases are also tested in the annual trials.

“Companies are enthusiastic about our tests as they can see comparisons of their varieties with others in the same location,” she says. “The tests are laborious and require specific knowledge, but we offer it for free with the support from NDSC. Because we are a third-party tester, companies and growers have faith in the scores.”

Miranda and her team visually assess farmers’ fields with known IDC issues, usually near Colfax and Leonard. The tests span six weeks with the first assessment taking place three weeks after planting. Miranda rates the plants visually on a scale of 1 through 5, with 1 being the healthiest. She returns to those same plants two weeks later to assess changes, and then one last time another two weeks later. The final IDC-resistance number for the variety is the average of these three scores.

“For example, I would give a plant the first score of 2.5 because it’s looking half yellow and half green, but the plant height is good,” she explains. “Then two weeks later, I see the plant has recovered some, so I’ll change the score to a 2. When I return for the last assessment, the plant may have collapsed under the stress of the iron deficiency, so I’ll score it a 5; or it completely recovers, and I can score it a 1.”

But Miranda also must take into account environmental conditions such as rainfall or drought, as well as field variability, as IDC is not uniformly present in a field. She says the more testing of the variety the better, in order to see the broader picture. Many varieties are tested each year to verify resistance or to spot intolerance. 

Iron deficiency chlorosis is caused by a high soil pH that neutralizes the acids released by the plant roots, which normally make the iron absorbable. The iron is present in alkaline soils, but it isn’t in a form that the soybean plant can take up. Soybean plants can recover from IDC, whereas with other diseases such as sudden death syndrome, the plant will eventually die. Miranda is testing soybean varieties that researchers have developed to overcome the iron transport issue.

“The soybean plant can grow back to compensate for the iron deficiency problems, but maybe it’s not as tall as it should be — stunting is a key symptom,” comments Miranda. “In a mildly tolerant line, the soybean may be resistant initially, but the new growth doesn’t receive iron. It’s really interesting to watch the changes.”

When a soybean recovers from IDC, it may look healthy enough, but stunting is common and seed development is usually affected, which can greatly reduce yields. Farmers need to know how the varieties could perform in their fields before they purchase seed, and these scores provide solid guidance. The trial results are published annually through North Dakota State University Extension.

Published: Nov 14, 2022