It Wasn't if, but when a corn cyst nematode would creep into fields, giving growers yet another critter of concern.
And even though the new cyst nematode that was discovered on corn in Tennessee is likely more susceptible to warmer soils, Corn Belt growers shouldn't feel comfort that it's only a southern problem.
“One of the good things corn producers have had going for them is there has been no major nematode problem,” says David Lightfoot, plant biotechnologist/pathologist, Southern Illinois University in Carbondale. “But nematode has been the one of the worst agricultural pests in the world. It [cyst nematodes on corn] was probably inevitable.”
Rotation to crops not susceptible to a particular cyst nematode, coupled with planting resistant seed varieties, has been the formula for controlling the pesky soybean cyst nematode (SCN). That could be the pattern growers need to follow if the new cyst nematode eventually emerges as a major problem on corn. Identifying one cyst nematode from another, however, could cause major problems for growers, as well as for pathologists involved in SCN research.
The new cyst nematode species was found in northern Tennessee in 2006, says Patricia Donald, USDA-ARS plant pathologist in Jackson, TN, adding that the new nematode was found because of “the good vision” of a pathology technician at the University of Missouri. The USDA Nematology Lab in Maryland confirmed identification this year.
The new cyst nematode, still yet to be distinguished scientifically, is separate from the SCN genus class of Heterodera glycines. It also is different from a corn cyst nematode, Heterodera zeae, discovered in Maryland and Virginia in 1981 after first being identified in India in about 1970, says Greg Tylka, Iowa State University plant pathologist. U.S. locations were quarantined and a culture of this nematode was kept at a USDA facility in Beltsville, MD. The quarantine was lifted in 1996 after no other corn cyst nematodes were found.
Tylka says it's unclear how damaging the new cyst nematode on corn found in Tennessee will be in the Midwest. “The true corn cyst nematode, Heterodera zeae, normally causes significant yield reductions only in hot environments, such as in India and Pakistan,” he says. “Currently, it's not possible to predict how the new cyst nematode might affect Iowa [or other Midwest] corn yields because details such as the length of the nematode life cycle, number of generations per season, optimum temperature, survival in frozen soil and ability to damage corn are not available.”
Disturbingly, the new cyst nematode can reproduce well at lower temperatures, like SCN does, Lightfoot says.
Donald says that diagnosis of the new cyst nematode will be difficult because of its resemblance to SCN. “Right now, the biggest problem in diagnosis is if there is a corn and soybean rotation,” she says. “The nematode on corn is slightly smaller than the SCN, but it's still hard to tell the difference.”
Lightfoot says growers should check for the new cyst nematode if they see stunted plants. “If they see unusual stunting, they should pull up corn and look at the roots,” he advises.
“If you have white females on the corn plant roots, it's an indication that there was reproduction and is not SCN,” Donald says.
Lightfoot is among those biotechnologists and pathologists holding their breath over the corn cyst nematode situation. He says finding genetic resistance to the new nematode could include looking at the two different kinds of resistance found for SCN. “The PI 88788 type of resistance for SCN has been yield friendly for growers,” he says. “The PI 437654 resistance is not as yield friendly but can provide resistance to all common types of Heterodera.”
Donald says other grassy plants have been tested against reproduction by the new cyst nematode on corn. “To date, corn is the most susceptible host, but there is some reproduction on other grass hosts,” she says.
Goosegrass and maybe ryegrass and other plants are susceptible to the new corn cyst nematode, Lightfoot says. After all, SCN can reproduce on hundreds of different plant species. Lightfoot says that plants newly studied for both SCN and corn cyst nematode resistance are thrale cress and hairy bittercress.
Tylka acknowledges that the new cyst nematode on corn may already be present in states other than Tennessee and adds that the message for corn researchers and breeders is to watch for it. “Growers should have it on their radar screen, but not necessarily in the center,” he says.
For more information on the potential for the corn cyst nematode, visit eppserver.ag.utk.edu/Extension/SPDN/2007/Cyst-nematode-corn/Cyst-Corn.htm or contact your local extension specialists.