October 31, 2004
From: ProMED-mail<promed@promedmail.org>
Source: American Phytopathological Society, Plant Disease Notes [edited] <http://www.apsnet.org/>

First report of soybean cyst nematode (Heterodera glycines) on soybean in North Dakota
C. A. Bradley, C. R. Biller, and B. D. Nelson, Department of Plant Pathology, North Dakota State University, Fargo, 58105. Plant Dis. 88:1287, 2004; published on-line as D-2004-0918-01N, 2004. Accepted for publication 7 Apr 2004.

During August 2003, soybean (_Glycine max_) plants from Richland County, North Dakota, with white-to-yellow lemon-shaped structures on the roots, were brought to the North Dakota State University Plant Diagnostic Laboratory. To confirm that the structures were females of a cyst nematode, they were crushed and observed microscopically to determine if nematode eggs and 2nd-stage juveniles were present. Morphology of the 2nd-stage juveniles was consistent with _Heterodera glycines_, the soybean cyst nematode (SCN).

A survey was conducted in soybean fields in 34 sq km around the field in which the samples originated. 10 of 20 fields surveyed had visible females on the roots of plants. Symptoms observed in those fields included patches of stunted, chlorotic, and dead plants.

Soil samples were collected from selected areas within 8 fields, eggs were extracted using standard soil sieving techniques, and egg numbers were determined. Egg numbers ranged from 550 to 20 000 eggs per 100 cubic cm of soil. SCN collected from 2 different fields, designated as Dwight and LaMars, were used to determine their HG Type.

Standardized procedures (1) were used in a growth chamber set at 27 C with 16-h days. Pots in the test were organized in a completely randomized design with 3 replicates; the test was repeated over time. After 30 days,
females were extracted from roots and counted, and a female index (FI) was calculated for each indicator line (1).

The mean number of females on susceptible standard cv. Lee 74, was 110. The Dwight SCN population had an FI of 5.3 on plant introduction (PI) 88788, 1.5 on PI 209332, 5.8 on PI 548316 (Cloud), and 0 on all other indicator
lines. The LaMars population had an FI of 1.0 on PI 88788, 3.1 on PI 548316 (Cloud), and 0 on all other indicator lines. These results indicate that both SCN populations tested are HG Type 0.

To our knowledge, this is the 1st report of SCN on soybean in North Dakota. Because other hosts of SCN, as well as soybean, are economically important in North Dakota, such as dry edible bean (_Phaseolus vulgaris_) and dry pea (_Pisum sativum_), this disease could adversely impact several commodities throughout the state.

Reference:
(1) T. L. Niblack et al. J. Nematol. 34:279, 2002.

[_Heterodera glycines_ [Hg] causes one of the most important diseases of soybeans. Yield losses can range up to 30 percent, mainly because fewer pods are produced on infected plants. Moreover, soybean yield is directly
related to the numbers of nematodes feeding on soybean roots. SCN-infected soybean is also more susceptible to infection by brown stem rot of soybean, caused by the fungal pathogen _Phialophora gregata_, in both resistant and susceptible soybean cultivars. Unfortunately, SCN cannot be eliminated from affected fields. The tough cyst, besides providing long-term protection for eggs and juveniles, allows for possible long distance dispersal. Cysts are found in "soil-peds" (aggregates of soil) which adhere to anything that moves through an infested field. To restrict spread of SCN to uninfested  areas, and to control populations in known infested fields, the following management practices are necessary; decontamination of farm implements and footwear, controlled movement of infested plants, weed control, crop  rotation, and use of resistant cultivars. A new bioassay for Hg has been developed and is described in the links below. The gist of the new test is that a low FI means the field's SCN population reproduces poorly on that line. A high number means a high rate of reproduction and that a variety from that line would be a bad choice for planting.

Links:
<http://www.planthealth.info/scn/scnhgtype.htm>
<http://www.cornandsoybeandigest.com/mag/soybean_new_test_beats/>
<http://ag.udel.edu/extension/information/pp/pp-02.htm>
<http://www.ag.uiuc.edu/cespubs/pest/articles/200209f.html>
- Mod.DH]