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First Report of Pathogenicity Group-3 of Leptosphaeria maculans on Winter Rape in Hungary

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 Ikervár, 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% relative humidity and a 16-h photoperiod. Seven days after sowing, cotyledons were wound inoculated with a 10-μl droplet of pycnidiospore suspension (1.5 × 10⁷ spores ml^-1). Interaction phenotypes (IP) were scored 10 days after inoculation using a 0 to 9 scale (1). All three isolates from Ikervár 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 first report of the presence of L. maculans PG-3 in Hungary. At the current time, PG-3 has caused at least 30% yield losses in susceptible cultivars of winter rape.

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