|Molecular Diagnostic for Corn Cyst Nematode||USDA FEDERAL DOMESTIC QUARANTINES: CORN CYST NEMATODE (CCN) 7CFR 301.90|
Heterodera zeae was first described from India by Koshy et al. where it is widely distributed. It has also been reported from Pakistan, the Nile Valley, Egypt, and Maryland in the USA In Maryland, it is found primarily in heavy silty-clay soils and population densities are usually sparse with 1-10 cysts/250 cu. cm soil. Although the corn cyst nematode could be indigenous to all of these areas, its apparently narrow distribution in the western hemisphere suggests recent introduction.
Symptoms of Damage
H. zeae infested plants exhibit poor and unthrifty growth and are stunted and pale green in color.
H. zeae was first recognized as distinct from H. avenae by its reproduction on maize and barley (Hordeum vulgare) but not on a number of other grains susceptible to H. avenae. All cultivars of Zea mays tested in Maryland, as well as Zea mexicana (teosinte), were susceptible. Other economic hosts include millet (Setaria indica), oat (Avena sativa), rice (Oryza sativa), sorghum (Sorghum bicolor), sugar cane (Saccharum sp.), and wheat (Triticum aestivum). Several grass weed hosts have been identified in India and the USA Populations from India and the USA appear to differ some in their host ranges. H. zeae has been associated with a number of dicots including legumes, solanaceous plants, cucurbits, crucifers, and many ornamentals, but reproduction has not been detected on any dicot. Populations from Pakistan are reported to be widespread on citrus, pear, and garlic, but these may also be field associations, and reproduction on these hosts has not been established.
|Biology and Life Cycle
Temperature plays an important role in the biology of H. zeae. The most favorable temperature for emergence of juveniles from cysts in 25 C, with 91% emergence. At temperatures of 10 or 15 C, only 10 to 20% of the juveniles emerge. Second-stage juveniles readily penetrate both the main root and lateral roots of the host, and a syncytium is initiated. The final molt to mature females with a gelatinous egg mass is completed in about 10 days, but eggs are not laid into the mass until about 14 days after penetration. Males, which are rare, apparently are not required for reproduction. Under conditions in Maryland, cysts with infective juveniles apparently only persist in fallow soil for about two years.
The life cycle is short, taking only 15-17 days if temperatures
are optimally warm (about 27-39 C). It has been speculated that the nematode
may complete six to seven generations during one crop season. H. zeae
is considered an economic pest in India and is a potential threat to
corn production in the USA. However, its spread and pathogenicity could
be restricted by high-temperature requirements (> 30 C) which are more
likely to be sustained in soils of the Southeast than in the corn belt
of the USA. Generally, the nematode reproduces well in moderately light
soils. The addition of clay to soil mixtures results in proportional decline
in nematode reproduction levels.
Since 1984, a quarantine has been imposed on the areas of Maryland infested with H. zeae but only a few tests have been carried out on its pathogenicity and strategies for management. Preliminary trials show that several fumigants reduce soil population density, but without an increase in corn yield. Crop rotation may be confounded by the wide host range. Sources of resistance in Zea mays are unknown.
Manual of Agricultural Nematology, William R. Nickle (editor), Marcel Dekker, Inc., 1991.
Plant Parasitic Nematodes in Subtropical and Tropical Agriculture, Michel Luc, Richard A. Sikora, and John Bridge, CAB International Institute of Parasitology, 1990