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Resistance

Helminthosporium and Stagonospora Leafspot Resistance are Unrelated to Indole Alkaloid Content in Reed Canarygrass. R. R. Sherwood, Research Plant Pathologist, Agricultural Research Service, U.S. Department of Agriculture, U.S. Regional Pasture Research Laboratory, University Park, PA 16802; K. E. Zeiders(2), and C. P. Vance(3). (2)Research Plant Pathologist, Agricultural Research Service, U.S. Department of Agriculture, U.S. Regional Pasture Research Laboratory, University Park, PA 16802; (3)Formerly Research Associate, Department of Plant Pathology, The Pennsylvania State University, University Park, Present address: Research Plant Physiologist, Agricultural Research Service, U. S. Department of Agriculture, Department of Agronomy and Plant Genetics, University of Minnesota, St. Paul, MN 55108. Phytopathology 68:803-807. Accepted for publication 31 October 1977. Copyright 1978 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-68-803.

Clones of Phalaris arundinacea representing a wide range of genetically controlled alkaloid concentrations were inoculated with Stagonospora foliicola or Helminthosporium catenarium. Resistance and susceptibility were found among both low-alkaloid and high-alkaloid clones. There was no apparent relation between disease severity and the type of alkaloids (gramine or tryptamine-carboline derivatives) in individual plants. Alkaloid concentrations in infected leaves did not differ significantly from the concentrations in noninoculated leaves. Radial growth rates of S. foliicola, H. catenarium, H. avenae, and Botrytis cinerea (the latter two fungi are not pathogenic on P. arundinacea) were measured on V-8 juice agar containing several alkaloids of reed canarygrass. Gramine, N-ω- methyltryptamine, N,N-dimethyltryptamine and 5-methoxy-N,N-dimethyltryptamine at 500 μg/ml caused little or no inhibition of growth. Hordenine slightly stimulated growth of H. avenae and B. cinerea. When inoculated leaf pieces were floated on cycloheximide solutions, the tissues became highly susceptible to penetration and colonization by all fungi, but the total alkaloid concentration of the tissues did not change. The results indicated that indole alkaloid concentration and alkaloid type in leaves are not related to resistance to S. foliicola or H. catenarium. Breeders can select lines combining low alkaloid levels with resistance to either, or both, of these pathogens.

Additional keywords: resistance mechanisms, papillae, Drechslera catenaria, Drechslera avenae, palatability, forage quality.