In the search for new disease-resistant elm species, some of the hottest prospects are homegrown.
Over at the University of Minnesota, they're torturing baby elms in pursuit of tomorrow's shade tree -- the one you're going to want on your boulevard in a few years.
The elms are lab-grown seedlings, cloned from Minnesota trees that show resistance to Dutch Elm Disease (DED). And the torture involves testing that resistance to the max. Researchers drill holes in the base, fill the holes with a lab-concocted culture of Dutch Elm fungus, cover the holes with tape -- and wait.
"It's pretty effective. It kills the susceptible ones pretty quickly," said U plant pathologist Benjamin Held.
But some seedlings survive. They appear to succumb initially, wilting and dropping leaves, just like their sickly full-grown cousins, the trees that end up with blaze-orange rings painted around their trunks. But the toughest seedlings recover. Those are the elms that will undergo further testing in the field, in hopes of eventually introducing a new, Minnesota-native landscape tree that can withstand the ravages of DED.
Disease-resistant elms are a hot topic in plant research and development circles.
"There's a lot of interest," said Chad Giblin, a U horticultural scientist. "The American elm is really important to Minnesotans. Many people grew up seeing streets lined with elms, then they were gone. People are very nostalgic about elms."
After DED wiped out entire neighborhoods of trees in the 1970s, green ash became a popular alternative. But now that a new scourge, the emerald ash borer, has been spotted near the Minnesota/Wisconsin border, the search for disease-resistant shade trees has gained urgency.
"We're trending back to disease-resistant American elms," said Mark Stennes, plant pathologist/arborist for S&S Tree Specialists in St. Paul. "In terms of size, shape and grandeur, there really is no substitute for the American elm."
Several disease-resistant elm species, such as Princeton and Valley Forge, are already available. But tree experts are cautiously optimistic about a few local cultivars that appear to combine Dutch Elm resistance with the added benefit of being ideally suited to Minnesota growing conditions.
And more is better when it comes to having disease-resistant species, according to plant pathologist Held. "You don't want to put all your eggs in one basket," he said. "The pathogen can change. That's why different selections are important, especially with trees, because they're worth a lot of money. A big boulevard elm can be worth thousands and thousands of dollars."
One of the most promising local elms being tested is the "St. Croix Elm," cloned offspring of a giant specimen growing on a hobby farm in Afton. Its owners, Chris and Tricia Bliska, bought the property several years ago, intending to start an organic orchard. The site was filled with elm trees, many infected with DED. But there was also an enormous, healthy elm, with a trunk about 75 inches in diameter, thriving in the front yard.
"It shows evidence of having been infected but seems to have the ability to overcome it," said Chris Bliska. The couple wanted to protect the tree with preventive treatment, so they hired Stennes, who soon became convinced that the century-old tree was something special.
"There were dead and dying elms all around it," he said. "It's had to live through unbelievable infection."
Stennes brought the tree to the attention of U researchers, who have a grant from the Minnesota Turf & Grounds Foundation to do elm-related research. The St. Croix Elm isn't the only local elm the U is cloning and testing. There are some promising specimens on city-owned parkland in Eden Prairie, as well as trees from Rogers and Kandiyohi. So far, the St. Croix Elm has fared the best in testing, according to Giblin. But further testing is needed to determine whether the cultivar can truly weather DED or is just showing juvenile resistance, Held said.
The Bliskas, Stennes and Giblin, who did the first cloning, have applied for and recently were granted a U.S. patent on the St. Croix Elm. They also have an agreement with Bailey Nurseries, which is doing its own testing, to produce the tree and bring it to market should it prove itself worthy.
"I don't know if it will ever be introduced for commercial purposes," Chris Bliska said. "We wanted the patent so we could control what happens to it."
Even with a patent, it will be several years before consumers could potentially see a St. Croix Elm at their local nursery. Tree development is a very slow process, Giblin said. "If interest in American elms stays high, I could see it as early as 2015."
Kim Palmer • 612-673-4784