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Crash Testing for Sclerotinia

Friday, December 1, 2000
filed under: Disease

Crash Testing for Sclerotinia

The new misting system for screening sclerotinia head rot is up and running at Carrington, ND. Its purpose: To evaluate how sunflower hybrids perform in the line of fire.

The new misting system at the North Dakota State University Research and Extension Center in Carrington, ND, is one place where crop scientists actually encourage Sclerotinia head rot to develop. The misting system allows crop scientists to evaluate the susceptibility of sunflower hybrids to Sclerotinia in an environment where disease inoculum and research conditions can be controlled for accurate analysis.

Comparing the testing of a new car with a new hybrid, the misting system is the crash-test stage. It is where sunflower hybrids are tested to see how they perform in the line of fire.

Misting systems (also referred to as crop disease “nurseries”) are already being used in Argentina and France to analyze Sclerotinia in sunflower. Several such misting systems are also being used in the United States to analyze disease susceptibility in other crops. Nurseries in Minnesota and other states are used to test susceptibility of wheat and barley lines to Fusarium head blight, or scab. In Illinois, a misting system has been used for five years to test soybean tolerance to Sclerotinia (also referred to as white mold).

The Carrington misting system, in its first year of operation in 2000, is the first in the U.S. dedicated to evaluating Sclerotinia head rot susceptibility of experimental and commercial sunflower germplasm for Sclerotinia tolerance.

Bob Henson, agronomist at Carrington and manager of the Sclerotinia screening project, says that the North Dakota State Board of Agricultural Research and Education and the National Sunflower Association contributed funding to help launch the misting system, with a project area of 1.25 acres. A fee was charged for commercial hybrid evaluation, and the fee will continue to be used each year to help underwrite the cost of screening.

Henson says 82 commercial hybrids were evaluated in 2000, along with 216 entries from the USDA, including advanced lines and some exotic material, in search of sources that would offer greater Sclerotinia tolerance.

There were three replications of each hybrid entered in the nursery, with the goal of having 10 plants to evaluate in each replication for every hybrid evaluated. Around the mid-flowering stage (R-5.5), Sunflower heads were sprayed by hand, with a spray bottle mixed with a solution of the ascospores that cause Sclerotinia. After sunflower heads are inoculated, about 36 to 48 hours of moisture is needed for infection to occur. That’s what the misting system, sprinklers with fine nozzles to create the mist, enables: A uniform infection to accurately assess the tolerance of sunflower hybrids to Sclerotinia.

Inoculations were conducted over a period of roughly three weeks, since not all entries in the nursery flowered at the same time. After the disease developed, plants were evaluated twice at two-week intervals, with scores given to each hybrid in four categories of infection: 1) No head rot; 2) Less than 50% infection; 3) 50%-99% infection; 4) 100% infection.

One facet of the Sclerotinia screening nursery was evaluating research methodology, or studying the effectiveness of research methods used to conduct screening. “We want to know how to run the system as efficiently as possible,” says Henson. “Every phase of this was a learning experience.”

Adjustments were made from lessons learned, which will carry over to next year’s screening as well. For example, a timer was used to turn on the misting system every half hour to create the constant humid environment needed for infection to develop. At first the timer was set to run for 10 minutes, then turn off. However, that resulted in too much moisture, so the misting time was later shortened to three minutes every half hour.

Spray patterns also needed to be adjusted to allow for wind carry. As well, Henson says they experimented with what to plant around plot margins, to help prevent lodging and wind carry. Sudan grass planted around the perimeter, followed by taller hybrids in the nursery, proved to be successful.

Even labeling inoculated heads for identification proved to be a challenge. Paper tags didn’t work because of the moisture. Thus, they switched to a water-resistant paper that can be fastened around the stem with a tool called a tapener.

The learning experience is continuing beyond the field: Henson says they are still evaluating the best means of compiling and reporting study results.

A smaller, more locally-focused misting system was also used in South Dakota this year to compare fungicides and screen about 10 of the most commonly planted sunflower hybrids in South Dakota, according to Marty Draper, South Dakota State University plant pathologist. Like the effort in Carrington, the system in South Dakota, funded in part through the South Dakota Oilseeds Council, is still being refined. “There’s a big learning curve, but we learned a lot about how to do it and hopefully we have more data to work with next year,” says Draper. “I think we’re on the right track.” – Tracy Sayler

Funding sought for Sclerotinia research

A research initiative focusing on sclerotinia (white mold) in sunflower and other crops will be included in a funding proposal to N.D. lawmakers in the 2001 legislative session.

North Dakota State University is seeking $165,000 in state funding for white mold research, which would involve several NDSU departments, including plant pathology, plant sciences, agriculture and biosystems engineering, and involve federal researchers as well, says Glen Statler, an official in NDSU’s agricultural department.

An integrated management approach is needed to get the disease under control, according to NDSU, requiring multi-faceted, multi-crop research in 1) genetics/breeding (screening for resistance); 2) fungicides (chemical control strategies); 3) production (rotation, tillage); 4) biological control; and 5) disease forecasting.

Losses from sclerotinia in 1999 are estimated at nearly $100 million in North Dakota alone. Sclerotinia head rot affected more than 80% of sunflower fields in eastern N.D. that year, reaching epidemic proportions not reached since 1986, according to NDSU.

There are no sclerotinia-resistant cultivars in beans, canola, or sunflower, but some cultivars are more susceptible to others. Other crops such as potatoes, safflower, flax, lentil, mustard, and crambe can also be infected if conditions favor the disease.

A separate multi-state, multi-crop national white mold research initiative is still in the works. Although federal funding wasn’t obtained for fiscal year 2001, Larry Kleingartner, executive director of the National Sunflower Association, would like to see a national effort regroup and try again to secure funding for FY 2002. USDA Agricultural Research Service national program staff rank white mold among the top of their priority list, notes NDSU.

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