April 26, 2006
From: ProMED-mail<promed@promedmail.org>
Source: American Phytopathological Society, Plant Disease Notes, May 2006 [edited] <http://www.apsnet.org/pd/searchnotes/2006/PD-90-0687A.asp>

First report of northern stem canker of soybean caused by Diaporthe phaseolorum var. caulivora in North Dakota
CA Bradley, Department of Plant Pathology, North Dakota State University, Fargo, 58105; S Li, Department of Crop Sciences, University of Illinois, Urbana 61801. Plant Dis 2006; 90: 687, published online as DOI:
10.1094/PD-90-0687A. Accepted for publication 10 Feb 2006.

In early September 2003, patches of soybean (_Glycine max_) plants in a field in Foster County, ND had dead branches with reddish brown cankers at the nodes. Stem tissue with cankers from 2 plants were excised and immersed in a 0.5 per cent NaOCl solution for one min, rinsed with sterilized distilled water, and placed into Petri dishes containing potato dextrose agar (PDA) amended with streptomycin sulfate (200 mg/liter). Four fungi were hyphal tipped and grown on PDA, acidified PDA, or water agar (WA) with soybean stem pieces incubated at 21 C with 24-h light and identified by culture and spore morphology after 3 to 4 weeks. Cultures were identified as _Diaporthe phaseolorum var. caulivora_ that produced white colonies with interspersed cottony tufts of mycelium on PDA (1). Stromata were small and scattered irregularly on the plate. Perithecia of the _D. phaseolorum var.
caulivora_ isolates were black and globose with 8-spored asci formed on soybean stem pieces on WA. To confirm pathogenicity of the _D. phaseolorum var. caulivora_ isolates, soybean plants (cv. NuTech 0606) were grown in the greenhouse and inoculated with recovered _D. phaseolorum var. caulivora_ isolates. The stems of soybean plants at the V3 stage were excised just below the 4th node. Mycelia plugs of the 4 different one-week-old cultures of _D. phaseolorum var. caulivora_ were placed into the large end of disposable micropipette tips (200 ul). The micropipette tip containing a _D. phaseolorum var. caulivora_ culture was subsequently placed over a cut soybean stem. The 4 _D. phaseolorum var. caulivora_ isolates were used to inoculate 10 stems apiece. To serve as controls, 10 cut soybean stems were inoculated with micropipette tips containing plugs of noninfested PDA, and 10 cut stems were not inoculated. Ten days after inoculation, micropipette tips were removed and lesions that had developed on the stem were measured. The mean lesion lengths of the _D. phaseolorum var. caulivora_ inoculated stems ranged from 48 to 82 mm and were significantly (P < 0.05) greater than the lesion lengths of the noninfested PDA (3 mm) and no PDA (one mm) controls. Northern stem canker was only observed in the one field; however, surveys were not conducted to determine the prevalence of the disease throughout the soybean-production area of North Dakota. To our knowledge, this is the 1st report of northern stem canker on soybean in North Dakota.

Reference:
1. FA Fernandez, et al. Stem canker. In: Compendium of Soybean Diseases, 4th edition. St Paul, MN: American Phytopathological Society, 1999: pp 33-5.

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[The crop plant soybean, _Glycine max_, develops symptoms of the disease northern stem canker when infected by the fungus _Diaporthe phaseolorum var. caulivora_.

Stem canker has been reported in Europe, South America, and in most soybean regions of Canada and the United States. This is the 1st report in North Dakota from samples collected in 2003, but it has been reported in South Dakota since at least 2000. In the USA, the disease is divided into northern stem canker and southern stem canker. Northern stem canker and southern stem canker are caused by _Diaporthe phaseolorum var. caulivora_ and _Diaporthe phaseolorum var. meridionalis_, respectively. Stem canker is closely related to pod and stem blight, which is caused by the related pathogen _Diaporthe phaseolorum var. sojae_.

Northern stem canker was 1st reported in the late 1940s in Iowa, and by the 1950s, the disease had spread into the upper Midwest and Canada. Southern stem canker was reported in the south in 1973, and by 1984, had been
detected in all southern states. Northern stem canker caused severe losses in the Midwestern and North Central Regions of the United States and Ontario, Canada in the late 1940s and early 1950s. Yield losses have been
reported to be as high as 50 to 80 per cent in naturally infested fields.
It became less significant as a problem when extremely susceptible varieties were removed from production. Southern stem canker arose as a problem in the southern United States in the 1970s and continues to be
significant problem for southern soybean farmers. A resurgence of Northern stem canker may be related to the deployment of susceptible varieties, changes in agronomic practices, changes in the pathogen population, as well
as seed sources.

Both pathogens can overwinter in infested soybean residue and may be spread with infested seed. Stem canker is effectively managed by the combination of planting resistant cultivars and reducing infested crop residue on the soil surface by deep plowing prior to planting a soybean crop. Delayed planting may be helpful. Seeds that are to be used for planting should not be harvested from fields with a history of stem canker. Fungicides applied
to the seed at planting can reduce the introduction of stem canker to a field but will not control infections in the field. Foliar fungicides can be effective when applied during vegetative stages; however, results are inconsistent, and in most cases, foliar fungicides would not be an economical management strategy.

Maps: N Dakota, USA: <http://go.hrw.com/atlas/norm_htm/ndakota.htm>
Foster County, ND: <http://www.city-data.com/county/Foster_County-ND.html>
Soybeans USA: <http://www.nass.usda.gov/research/atlas02/Crops/Fieldpercent20Cropspercent20Harvested/Soybeans/Soybeans percent20forpercent20Beans, percent20Harvested percent20Acres-dot.gif> 
Pictures:
Stem canker: <http://ohioline.osu.edu/b895/images/b895_21.jpg>
Leaf symptoms: <http://cipm.ncsu.edu/ent/SSDW/atlas11.gif>
Pod symptoms: <http://www.ipmimages.org/images/384x256/1235156.jpg>
Links: <http://www.plantpath.wisc.edu/soyhealth/pdf/stemcanker_06.pdf>
<http://www.soydiseases.uiuc.edu/index.cfm?category=diseases&disease=95>
<http://ohioline.osu.edu/b895/b895_13.html> - Mod.JAD]

[see also in the archive:
2004
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Diaporthe spp., stem canker, soybean - USA (WI) 20040519.1340
2002
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Diaporthe spp. soybean stem canker - Argentina 20021201.5944
2001
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EPPO Alert List: New Listings (02) 20011201.2923
Diaporthe spp., soybean stem canker - Argentina 20010227.0387]