|Smiley, Richard - OREGON STATE UNIV., OR|
|Yan, Guiping - OREGON STATE UNIV., OR|
Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 11, 2008
Publication Date: June 12, 2008
Citation: Smiley, R.W., Yan, G.P., Handoo, Z.A. 2008. First record of the cyst nematode Heterodera filipjevi on wheat in Oregon. Plant Disease. 92(7):1136. Interpretive Summary: Plant-parasitic nematodes are microscopic worms that attack plant roots and cause an estimated ten billion dollars of crop loss each year in the United States and 100 billion dollars globally. Cyst nematodes are an important problem damaging the roots of many kinds of plants worldwide, including wheat in Oregon. This brief report describes how a team of Oregon State University and ARS scientists identified a species of cereal cyst nematode different from the common cereal cyst nematode already known to infest wheat fields in Oregon. This discovery is significant because it is the first report of this nematode in North America. Consequently, the results will be used by researchers planning future nematode surveys and creating and recommending grain varieties with resistance to the new species.
Technical Abstract: Plant and soil samples from an irrigated winter wheat field in Union County, Oregon, were evaluated for root diseases during the spring of 2007. Stunted seedlings exhibited chlorotic or necrotic lower leaves, apparently healthy younger leaves, few or no tillers, rotting of lower culms and crowns, and light-brown roots with little or no branching. Signs and symptoms of fungal pathogens (Pythium spp., Gaeumannomyces graminis var. tritici, Rhizoctonia solani AG-8 and Typhula incarnata) were present on affected plants. Extraction of motile nematodes from soil revealed high populations of Pratylenchus neglectus (6,560/kg of soil), Tylenchorhynchus spp. (2,369/kg) and a species initially thought to be Heterodera avenae (3,098 juveniles/kg). The morphology of cysts, second-stage juveniles and molecular analysis established the identity of the species as the cereal cyst nematode Heterodera filipjevi (Madzhidov, 1981) Stelter, 1984. Morphological characters used for identification included cyst shape, characteristics of cyst terminal cone including nature of fenestration, cyst wall pattern, length of vulval slit, and presence of underbridge and bullae. For second-stage juveniles, critical criteria were body and stylet length, shape of stylet knobs, shape and length of tail and hyaline tail terminus, and number of lines in the lateral field. For PCR-RFLP diagnosis, four restriction enzymes applied to amplified DNA of cysts from the infested field consistently revealed a pattern identical to that of a H. filipjevi DNA standard and distinct from patterns of H. avenae, H. schachtii, and H. latipons. Detection of H. filipjevi in Oregon represents a new record for the occurrence of this species in the United States and apparently also for North America.