Ames, Iowa
July 30, 2007
Source:
Integrated Crop
Management IC 498 (21) -- July 30, 2007 issue
Iowa
State University
New cyst nematode species on
corn
by Greg Tylka, Department of Plant Pathology
Iowa crop producers and
agronomists are well aware of soybean cyst nematode (SCN), the
plant-parasitic nematode that is widespread through the Midwest
and can seriously reduce soybean yields. And many people are
aware of other plant-parasitic nematodes that can cause
significant yield reductions on corn. But most crop
professionals probably are unaware that there is a corn cyst
nematode that has been in the northeastern United States since
1981. And just recently, a new cyst nematode species that
reproduces on corn was discovered in Tennessee.
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Adult females and cysts of the soybean cyst
nematode. (G. Tylka) |
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| Adult
females and cysts of the nematode discovered on corn
in Tennessee in 2006. (R. Heinz and M. Mitchum) |
Corn cyst nematode known in
United States since 1981
The corn cyst nematode, Heterodera zeae, initially was reported
in India in 1970. It was first discovered in the United States
in Kent County, Maryland, in 1981. The corn cyst nematode has
been found only in four counties in Maryland (Cecil, Harford,
Kent, and Queen Anne's) and in Cumberland County, Virginia. The
fields known to be infested with the corn cyst nematode were
quarantined by the United States Department of Agriculture in
1981, but the quarantine was lifted in 1996.
The biology of the corn cyst nematode is similar to that of SCN.
The life cycle takes 18-21 days under ideal conditions, and
several generations can occur in a growing season. The ideal
temperature for the corn cyst nematode is 86 °F, which is
considerably higher than the 78 °F optimum temperature for SCN.
All of the numerous corn hybrids tested in the 1980s in Maryland
were susceptible to the corn cyst nematode. Other host plants of
the corn cyst nematode include barley, oats, rice, sorghum,
sugarcane, wheat, and several grass weeds.
New species of cyst nematode discovered on corn in 2006
On July 29, 2007, at a scientific conference, university
nematologists from Missouri, Nebraska, and Tennessee and USDA
nematologists announced that a new cyst nematode species was
discovered on corn. Juveniles and cysts (egg-filled, dead
females) were discovered in a soil sample taken from a field of
stunted corn in northwestern Tennessee (Obion County) in 2006.
University of Missouri nematologists made the discovery and
verified reproduction of the nematode on corn and also found no
reproduction on soybean in greenhouse tests. The nematode
reproduced well on many different corn hybrids but poorly on
other monocots. No dicots were found to be hosts. The cysts of
this nematode look different than those of the corn cyst
nematode discussed above, and genetic analyses confirmed that
the nematode was not the corn cyst nematode. The nematode
appears identical to a cyst nematode discovered on goosegrass, a
weed, in Lauderdale County, Tennessee, in 1978.
Will new cyst nematode species affect corn production in
Iowa?
It is difficult to predict whether the new cyst nematode
discovered on corn in Tennessee will move into other states and
eventually reach Iowa. But in the 11 years since the quarantine
was lifted on the fields infested with the corn cyst nematode in
Maryland and Virginia, the nematode has not been found in any
other state.
It also is unclear how damaging the new cyst nematode discovered
in Tennessee would be to corn if it moved to the Midwest. The
corn cyst nematode, H. zeae, causes significant yield reductions
only in hot environments, such as in India and Pakistan.
Currently, it is not possible to predict how the new cyst
nematode discovered on corn in Tennessee might affect Iowa 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.
New cyst nematode species on corn would hinder SCN field
sampling and research
Spread of this new cyst nematode on corn into fields in the
Midwest would seriously hinder field soil sampling as well as
research on the biology and management of SCN. Currently, no
other cyst nematode species commonly exist in Iowa corn and
soybean fields, and eggs recovered from cysts extracted from
Iowa soils are assumed to be SCN eggs. But eggs of SCN and other
cyst nematodes look similar and cannot be distinguished by
appearance. Determining SCN egg population densities for
management or research purposes would be impossible using
current techniques if other cyst nematodes were present. A stain
that is specific for SCN eggs currently is not available, and
developing such a stain likely would take years.
Greg Tylka is a professor of plant pathology with extension
and research responsibilities in management of plant-parasitic
nematodes.
This article originally appeared on pages 239-240 of the
IC-498(21) -- July 30, 2007 issue
http://www.ipm.iastate.edu/ipm/icm/2007/7-30/nematode.html |
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