Challenging Year for Disease Research
It was a challenging summer for Sclerotinia head rot and stalk rot research in 2006. There was the sudden death of Bob Henson at the NDSU Research Extension Center at Carrington, N.D., who was a key leader in this research effort. Then there was the hot, dry weather – to evaluate hybrids for disease, you need essentially the opposite.
Fortunately, misting systems (also referred to as crop disease “nurseries”) were in place to ensure reliable disease evaluation, despite the dry weather.
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.’
Around mid flowering, sunflower heads are sprayed with a solution of the ascospores that cause Sclerotinia, to induce head rot infection. After sunflower heads are inoculated, about 36 to 48 hours of moisture is needed for infection to occur. That’s what the misting system comes in. Sprinklers with fine nozzles create mist, enabling a uniform infection to accurately assess the resistance of sunflower hybrids to Sclerotinia.
Henson had become known as the ‘guru’ of misting. He oversaw creation of the misting system at Carrington, the first in the U.S. dedicated to evaluating Sclerotinia head rot susceptibility of experimental and commercial sunflower germplasm for Sclerotinia resistance.
The first year of operation in 2000, 82 commercial hybrids were evaluated, along with 216 entries from the USDA, including advanced lines and some exotic material, in search of sources that would offer greater Sclerotinia head rot resistance.
“Every phase of this was a learning experience,” Henson said, after the first year of testing. “We want to know how to run the system as efficiently as possible.”
Lessons were learned and adjustments were made in the early years of screening, everything from the best sprinkler timing to the right spray pattern, to the best means of compiling and reporting evaluation results. Even labeling the sunflower heads to identify the hybrids from one another proved to be a challenge. After the first year of mist testing, upon realizing that soggy paper ID tags don’t remain fastened around sunflower stems very well, Henson switched to water-resistant tags for hybrid identification.
Fast forward to 2006, and while Bob Henson will be missed, he leaves a foundation of systematic research methodology used by other researchers in more locations and in other crops.
The Carrington location now has Sclerotinia misting sites for other broadleaf crops such as edible beans, canola, and field peas. In addition to Carrington, there are now misting evaluation sites in Brookings, S.D., Morden, Manitoba, Langdon and Oakes, N.D., and Crookston, Minn.in 2006. Much of this research is supported in part by the National Sclerotinia Initiative (www.sclerotinia.com).
As well, stalk rot resistance evaluation was added in 2005. Sunflower is the only commercial broadleaf crop that is susceptible to Sclerotinia root infection, and this is how stalk rot occurs.
Tom Gulya, USDA-ARS sunflower pathologist in Fargo, N.D., has developed a novel system to test hybrids and inbreds for resistance to root infection. He grows the fungus in the lab on millet and then knives it into the soil about 8 inches from the plant in the late vegetative stage. This method infects plants for stalk rot resistance evaluation.
There are two phases of hybrid screening for Sclerotinia head and stalk rot resistance. The first is ‘initial screening,’ in which 75 hybrids were tested for head rot at Carrington and Morden in 2006. ‘Repeat screening’ is the second, more advanced phase of evaluation, in which 20 of the best hybrids from the initial screen are retested at five sites.
Blaine Schatz, director and agronomist at NDSU Carrington, says that the importance of the misting systems to Sclerotinia head and stalk rot disease evaluation was verified in 2006. The misting nurseries are producing valuable data to identify significant differences among hybrids for disease resistance.
Results from initial screening suggest many good hybrid candidates for continued evaluation, he says, and repeat screening results indicate that sunflower seed companies in cooperation with USDA scientists are making positive advances in developing hybrids with improved resistance.
Growers who dropped the crop after the devastating head rot season in 1999 would not recognize many of the new hybrids today. In fact, one of the most popular hybrids commercially grown in 1999 is used as the vulnerable check in both the head and stalk rot nurseries.
The table shows the top 20 performing hybrids in repeat screening for head and stalk rot in 2006. Complete data, including initial screening results, can be found online at www.sunflowernsa.com – go to the ‘Research’ link. – Tracy Sayler
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