First report on Pyrenophora teres causing lesions of wheat leaves in Hungary

During routine surveys of wheat (Triticum aestivum L.) in growing areas of Hungary, diseased leaf samples were collected from different wheat cultivars. Leaves exhibited dark brown necrotic lesions with or without a chlorotic ring. Single conidia were isolated from necrotic tissue fragments under a stereo microscope, and transferred onto potato dextrose agar (PDA). Macro- and micromorphological examinations of single-spore isolates indicated some of them to be Pyrenophora teres (anamorph: Drechslera teres), which is a well-known barley pathogen. This species produces fuliginous to yellowish or olivaceous brown conidia with round basal cells, and in most cases several conidia are produced on a single conidiophore (Shoemaker, 1962, Sivanesan, 1987). Sequences of the ITS region of the isolates were compared to those of P. teres isolates in the Genbank database. The ITS sequences of these isolates were identical to P. teres ITS sequences (accession numbers: Y08746, AF400889-AF400892). Of the 30 isolates studied, the ITS sequences of three isolates were submitted to GenBank under accession numbers EF186672-EF186674.

Pathogenicity tests were conducted in greenhouse experiments by inoculating the leaves of barley and wheat plants at the two leaf stage with conidial suspensions of 3×10³ conidia ml^-1 of the P. teres isolates. Twelve days after inoculation symptoms similar to those observed on naturally infected plants were produced (Figure 1). Pyrenophora teres was reisolated from infected leaves (Figure 2). Conidial colonies grew rapidly forming mid or light grey mycelia with white tufts covering the surface (Figure 3). To our knowledge this is the first report on the pathogenicity of P. teres on wheat in Hungary. This species has been isolated previously from wheat in Canada and other parts of the world (Turkington et al., 2002, Zillinsky, 1983). Pyrenophora teres was isolated from 0-9% of spots observed on leaf samples with disease symptoms depending on the geographical location of the fields in Hungary. Our data indicate that wheat can serve as host for P. teres, rising doubts on the applicability of pre-treatment of wheat with P. teres to control other fungal pathogens as suggested by Nolan and Cook (2000).