September 28, 2005
From: British Society for Plant Pathology, New Disease Reports, Vol. 12 [edited] <http://www.bspp.org.uk/ndr/jan2006/2005-69.asp>

First report of tan spot caused by Pyrenophora tritici-repentis (anamorph Drechslera tritici-repentis) in Bulgaria
M. Todorova, University of Forestry, Faculty of Agriculture, Bull. Kliment Ochridski 10, Sofia 1756, Bulgaria. Accepted for publication 8 Aug 2005.

In June 2004, an unknown leaf spot was observed on wheat, rye and triticale collected from commercial fields in different geographic regions of Bulgaria. The visible symptoms were oval to elongated brown spots surrounded by a chlorotic halo.

Conidiophores in the necrotic tissues were long, mainly single, hyaline or dark brown. Conidia were cylindrical, 90-220 x 10-16 micrometers with a conical terminal cell at the base and 3-9 septa. Consequently, the fungus was identified as _Drechslera tritici-repentis_, as described by Hunger & Brown (1987), Ellis (1976) and Shoemaker (1962). In follow-up collections made in March-April 2005, the teleomorph _Pyrenophora tritici-repentis_ was identified in straw debris collected in North Bulgaria. Pseudothecia were setate, dark brown and spherical. Asci with 8 ascospores -- with 3 transverse and one longitudinal septum -- were observed (Shoemaker, 1962).

Conidia and ascospores plated onto PDA formed white to grey cottony colonies secreting a brown pigment. Young wheat plants (second leaf stage) were inoculated with a mycelial suspension by spraying, placed in a moist chamber for 24 hours and then incubated under greenhouse conditions. After 7-8 days, the typical brown spots with chlorotic halo were observed.

_Pyrenophora tritici-repentis_ is one of the most common and economically important diseases in many Western European countries. During the last decade, it has been reported in Ukraine, Latvia, Russia, Czech Republic and
Hungary (Sarova et al., 2003). It is likely that wet weather, reduced tillage and lack of crop rotation has favored its spread in Bulgaria.

References:

Ellis MB, 1976. Dematiaceous hyphomycetes. Wallingford, Oxon, UK: CAB International.

Hunger RM, Brown DA, 1987. Colony color, growth, sporulation, fungicide sensitivity, and pathogenicity of Pyrenophora tritici-repentis. Plant Disease 71, 907-910.

Sarova J, Hanzalova A, Bartos P, 2003. Incidence of wheat leaf spot pathogens in the Czech Republic. Cereal Research Communications 31, 145-151.

Shoemaker RA, 1962. Drechslera Ito. Canadian Journal of Botany 40, 809-936.

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[Tan spot commonly infects wheat in the Canadian prairies. Resistance to tan spot is not widely dispersed in the International Maize and Wheat Improvement Center (CIMMYT) germplasm, but moderate resistance is known to
occur (Rees and Platz, 1992). Some newer CIMMYT lines, such as Milan, Attila, Corydon and Tinamou, and some Chinese wheats and their derivatives, such as Luan, are also reported to carry high to moderate resistance (Diaz
de Ackermann and Kohli, 1998). Tan spot is increasing in areas where reduced tillage practices are being combined with stubble retention. CIMMYT has an ongoing project to search for new and better sources of resistance to tan spot for these areas.

The fungus over-winters on infected wheat straw or stubble. Spores are dispersed primarily by wind. Wheat is the primary host, but forage grasses and rye are alternate hosts. Barley and oats are highly resistant to tan
spot. Ways to reduce tan spot include rotating between cereal and broadleaf crops, such as oilseeds and pulses, planting disease-free seed or seed that has been treated with a recommended fungicide, planting cultivars with
known resistance to one or more leaf spot diseases, and, if leaf spots are present and rain is forecast, applying a registered foliar fungicide might be advisable.

Links:
<http://www.fao.org/documents/show_cdr.asp?url_file=/DOCREP/006/Y4011E/y4011e0b.htm>
<http://www.omafra.gov.on.ca/english/crops/facts/83-046.htm>
<http://www.agr.gov.sk.ca/DOCS/crops/cereals/Cpt038.asp?firstPick=Crops&secondpick=Cereals&thirdpick=Null>
<http://www.gov.mb.ca/agriculture/crops/diseases/fac43s00.html>
- Mod.DH]

[see also in the archive:
2003
Tan spot, wheat - USA (Pacific Northwest) 20030211.0367]