Researchers testing wild Aussie sunseeds for resistance

FARGO, N.D. -- Scientists at the Agricultural Research Service's Sunflower Research Unit in Fargo, N.D., are working to identify genetic traits of wild sunflowers collected in Australia last year that may help create sclerotinia resistance in cultivated hybrids.

Sclerotinia sclerotiorum is a pathogenic fungus that causes three major diseases in sunflower cops. Commonly referred to as head rot, stalk rot and root rot, these white mold pathogens are the most damaging for sunflowers producers all over the world.

Gerald Seiler is a research botanist at the ARS unit at the Northern Crops Science Laboratory in Fargo. The unit is the only public facility in the United States dedicated to the plant. He thinks that looking into wild species offers real hope in fighting the mold.

"We've now got some very good potential sources of genes," he says. "We looked at this material for sclerotinia because this (disease) is 70 percent of our research."

Origins

The sunflower, as a crop and as a wild species, is native to North America. Beginning in the 1500s, it was taken back to Europe, where it was used in gardens and eventually as a crop plant for its seed. In the late 1800s and early 1900s, the evolved seeds began making their way back.

"When the immigrants came, a lot of the material came back to the U.S. They form the basis of a lot of our genetic material that's currently used in sunflowers," Seiler says.

The SRU researchers believe that during that same time period, sunflowers, through either the European-grown seeds, or directly from America, made their way to Australia.

"That's still speculation," he cautions. "All we know is that they're not native there because we know that they are native here."

Since that time, though, sunflowers have become naturalized. They've mutated and evolved to survive the new environments as they spread across the Australian continent. They now are considered, he says, part of the weedy vegetation of these areas.

"This is true in Argentina, and it's true in Australia and Europe," Seiler says.

What is interesting to Seiler is that these wild weeds may have learned how to resist diseases all on their own.

"The theory is that if they grow in an area where there's a lot of fungal diseases and they survive, they either had genetic resistance or they had some type of avoidance mechanism to not get the pathogen," he says.

An avoidance mechanism in a sunflower may mirror some of our own agricultural practices. For instance, it may emerge, go to seed and die early enough in the season to avoid fungal disease altogether, just as producers will plant early to avoid certain diseases.

The point he makes is that plants grow where they grow because they can survive there, and if they've survived in a disease-rich environment, researchers may be able to find the key to their survival.

"What we do is bring the material home, we grow it and then we test it in the greenhouse," he says. "The basis of breeding these genetics is that we want durable resistance. We want something that we can put genes in that have resistance to various pathogens or factors. It can be insects, too."

The unit researchers can breed plants and instill a trait into plants so it can last across multiple generations versus using a chemical on each one. But some of these pathogens are unaffected by the available chemicals, Seiler points out. The only choice there is to breed for resistance, despite the fact that it is an inherently slow process.

"It takes 10 years to develop a hybrid, from beginning to end," Seiler says. "We start with these wild relatives that are way down the stream."

Gathering and testing

Seiler made the trip with research unit plant pathologist Tom Gulya to Australia, where they were joined by three Australian researchers to make up small canvassing teams. They covered the eastern, western and southern coastal regions, where sunflowers have taken hold. Detailed notes were required.

"Location is the most important thing," Seiler says, "but we also looked at soils, habitat and related species."

Many species are site-specific, he says. There are 51 species of sunflowers, 37 of which are perennial and 14 are annual. The Aussie/SRU team was looking for five annual species that have been identified in Australia, but with just two weeks to cover all that ground, they only located three.

Seiler and Gulya returned March 14, 2007, and would have been able to plant some test beds right away, except that the seeds had to be quarantined for six months. After that, they sent seeds of each species to the seed bank in Ames, Iowa.

"The important thing is, we put this material in a gene bank and we preserve it because we don't know what's going to challenge us in the future," Seiler says.

As for the seed, they will try to discover how it got to Australia.

"First we'll see whether the genes match up between here and there," Seiler says. "If they don't, then our speculation is completely wrong."

Aside from that, there still is an added bonus in all this work to bring the samples back.

"Once we have the material, we can look at it for anything," he says. "This is the beauty of the germplasm gene bank. We don't have to have something specifically in mind because we don't know what genes are there."

Seiler contrasts that to looking at the cultivated material, as they did for many years.

"It has a very narrow genetic base, so there's not a lot of differences between all the hybrids you see grown out there," he says.

They will be making crosses onto these elite cultivated materials using the wild pollen, he says, but there will be hurdles.

"Every time you start messing with the good, the cultivated hybrids, you always take a hit in some other factor, especially when you're dealing with these wild species that are very distant cousins. So we take small, baby steps," he says.

They are making progress and the material has been evaluated in the greenhouse plantings. The first field planting recently was completed.

"Sometimes you don't get the same results," Seiler says. "You have difficulty selecting because you select one in the greenhouse and it looks resistant and then we put it in the field, and it's not."

But the research to wipe out sclerotinia will continue at the Sunflower Research Unit, and it is apparent they will go where they have in search of the answers.