April 19, 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-90-0684C.asp>

First report of pathogenicity group-3 of Leptosphaeria maculans on winter rape in Hungary
Sz. Szlavik, National Institute for Agricultural Quality Control, Budapest, 1024 Hungary; T. Barasits, Plant Protection and Soil Conservation Service of County Vas, Tanakajd, 9762 Hungary; and W. G. D. Fernando, Department of Plant Science, University of Manitoba, Winnipeg, MB R3T 2N2, Canada. Plant Dis. 90:684, 2006; published on-line as DOI: 10.1094/PD-90-0684C. Accepted for publication 9 Feb 2006.

Blackleg, caused by _Leptosphaeria maculans_, is an increasing threat to winter rape (_Brassica napus_ L.) in Hungary. The winter rape acreage has been increasing, and the occurrence and severity of the disease has become widespread in all rapeseed-growing regions throughout Hungary in a very short time. The blackleg-infected rape stubbles were collected in the autumn of 2003 in Ikervar, County Vas, where the disease was severe. Ascospores were obtained from pseudothecia growing on infected rape stubble (susceptible cvs. GK Helga and Aladin). Three single-spore cultures were grown on V8 agar medium at room temperature and fluorescent light. The culture characteristics fit the type culture description for _L. maculans_. Pycnidiospores that formed on V8 plates were flooded with 10 ml of sterile distilled water. Seeds of cvs. Westar, Glacier, and Quinta obtained from the Department of Plant Science, University of Manitoba, Canada were sown in plastic pots containing peat mix. Seedlings were maintained in a growth chamber at 24 C with 90 percent relative humidity and a 16-h photoperiod. Seven days after sowing, cotyledons were wound inoculated with a 10-ul droplet of pycnidiospore suspension (1.5 _ 10(^7) spores ml(^-1)). Interaction phenotypes (IP) were scored 10 days after inoculation using a 0 to 9 scale (1). All 3 isolates from Ikervar were highly virulent on cvs. Westar (8.8 to 8.9) and Glacier (8.1 to 8.3) and avirulent on cv. Quinta (0.8 to 0.9). The IP ratings indicated that these isolates belonged to pathogenicity group-3 (PG-3). To our knowledge, this is the 1st report of the presence of _L. maculans_ PG-3 in Hungary. At the current time, PG-3 has caused at least 30 percent yield losses in susceptible cultivars of winter rape.

Reference: (1) A. Mengistu et al. Plant Dis. 75:1279, 1991.

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ProMED-mail
<promed@promedmail.org>

[The crop plant rape/rapeseed or canola, _Brassica napus_, develops symptoms of the disease black leg when infected by the fungus _Leptosphaeria maculans_.

Black leg (aka Phoma stem canker) is an economically important and serious disease of canola (_Brassica napus_) in Australia, France, Germany, USA, Canada and the United Kingdom. The infections of blackleg may occur on cotyledons, leaves, stems and pods. Stem canker is the most serious symptom, as it can girdle the stem, causing plant lodging leading to yield loss. Three disease prevention methods -- crop rotation, genetic resistance and seed treatment with fungicide -- have proven to be effective.

Isolates of canola can be categorized into 4 pathogenicity groups (PGs) on the basis of the interaction phenotypes (IP) on the differential canola cultivars Westar, Glacier, and Quinta by using a standard screening protocol in the greenhouse. Isolates in PG1 are weakly virulent, as they generally cause superficial lesions on the
leaves. However, isolates in PG2, PG3, and PG4 are highly virulent because they can produce stem canker at the base of the canola plant, causing significant yield loss. PG3 isolates (virulent on cv. Westar and Glacier; avirulent on Quinta) are found in Europe, Australia, USA and Canada. This article describes the 1st report of the presence of _L. maculans_ PG3 in Hungary and will be useful when choosing which varieties to grow.

Map: Hungary
<http://go.hrw.com/atlas/norm_htm/hungary.htm>

Pictures:
Stem canker
<http://www.oregin.info/images/canker.jpg>
Pycnidia
<http://www.canola.okstate.edu/cropproduction/diseases/blacklegdisease.jpg>
General
<http://www.rothamsted.ac.uk/ppi/ppigallery.html>

Links:
<http://www.rothamsted.ac.uk/ppi/diseases/sc.html>
<http://www.niab.com/FILEAREA/lmaculans1.htm>
- Mod.JAD]

[see also in the archive:
2005
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Blackleg, canola - Argentina (02) 20050813.2368
Blackleg, canola - USA (ND): 1st report 20050626.1807
Blackleg, canola - Argentina: 1st report 20050319.0807
Blackleg, canola, path.gr.4 - Canada (MB): 1st report 20050302.0648
2003
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Blackleg, canola - Canada (Manitoba) 20030918.2367
Blackleg, canola - Australia (WA, NSW, SA, VIC) 20030503.1105
Blackleg, canola - Brazil (Rio Grande do Sul) 20030225.0478
2001
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Blackleg, root infection, canola - Australia (SA, NSW) 20010819.1959
2000
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Blackleg, canola - Australia (NSW) 20000615.0980]