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Variability in virulence as determined by honeydew production by strains of Claviceps purpurea (Fr.) Tul. on eight genotypes of wheat.
J. MENZIES (1), A. Gordon (2), D. O'Sullivan (3). (1) Agriculture and Agri-Food Canada, Morden, MB, Canada; (2) National Institute of Agricultural Botany, Cambridge, United Kingdom; (3) University of Reading, Reading, United Kingdom

Ergot, caused by <i>Claviceps purpurea</i> has steadily increased in incidence and severity on the Canadian prairies since 1999. The development of resistant wheat lines is being explored. The variability in pathogenicity among strains of <i>C. purpurea</i> in nature is not known. The objective of this work was to study variability in pathogenicity among different strains of <i>C. purpurea</i> for honeydew production on wheat lines differing in levels of resistance. Forty seven pathogen strains from the Canadian prairies and the United Kingdom were inoculated onto 3 durum wheat (<i>Triticum aestivum</i> L. var. <i>durum</i>) lines (‘Melita’, ‘Kyle’, and 9260B-173A) and 5 hexaploid wheat (<i>T. aestivum</i>) lines (‘Cadillac’’, ‘Vista’, ‘Kenya Farmer’, ‘Lee’, and HY630). Nine spikes per wheat line were needle inoculated prior to anthesis for each pathogen strain using a conidial suspension. Each spike was assessed for honeydew production 14 days after inoculation using a scale of 1 to 4; 1=no honeydew visible, 2=honeydew confined within glumes, 3=honeydew exuding from florets in small drops, and 4=large drops of honeydew running down the spike. There were significant differences among the 8 wheat genotypes for the mean honeydew production. Pathogen strains were considered to be virulent when they produced a honeydew rating of 2.5 or higher. Different virulence phenotypes were identified, and there was a wide range of genetic variability among strains of <i>C. purpurea</i>.

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