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Resistance

Histochemistry of Papillae Formed in Reed Canarygrass Leaves in Response to Noninfecting Pathogenic Fungi. R. T. Sherwood, Research Plant Pathologist, U.S. Regional Pasture Research Laboratory, Agricultural Research Service, U.S. Department of Agriculture, University Park 16802; C. P. Vance, Research Associate, Department of Plant Pathology, The Pennsylvania State University, University Park 16802. Phytopathology 66:503-510. Accepted for publication 24 October 1975. DOI: 10.1094/Phyto-66-503.

Leafspot fungi which were nonpathogenic to reed canarygrass but pathogenic to other plants, formed appressoria and penetration pegs on reed canarygrass leaves. Papillae usually formed in the outer epidermal walls beneath penetration pegs and no penetration occurred. The epidermal walls became histochemically modified in disk-shaped areas, up to 60 µm in diameter, around the sites of attempted penetration. Lateral epidermal walls beneath the disks (disk-shaped areas) became swollen and histochemically modified. Papillae in leaves inoculated with Helminthosporium avenae gave histochemical reactions with toluidine blue O, chlorine water-sodium sulfite, and phloroglucinol-HCl which indicated that lignified material was a major structural component of the core of the papillae and the altered lateral walls and only a minor component of the disks. Insolubility in 72% H₂SO₄ and solubility in chlorine-sulfite supported these conclusions. Tests with resorcinol blue, lacmoid, and aniline blue-fluorescence indicated that callose was present in the papillae, lateral walls, and disks. Results from tests with IKI-H₂SO₄ and toluidine blue O, and for birefringence suggested that cellulose was a significant structural component of the disks, the altered lateral walls, and the cover layer of the papillae. Tests for cutin, suberin, tannins, gums, and pectic compounds were negative. Callose was more readily demonstrated 10-12 hours after inoculation with H. avenae than at later times. Lignification was detected at 10 hours, and was strong after 24-48 hours. Six clones of reed canarygrass had the same structural and histochemical reactions. Papillae and wall modifications formed at 17, 24, and 29 C in continuous light or dark had similar histochemical reactions. Positive tests for lignified material, callose, and cellulose were obtained in papillae, disks, and lateral walls associated with penetration attempts by Botrytis cinerea, Leptosphaerulina trifolii, Stagonospora arenaria, Stemphylium botryosum, Helminthosporium catenarium, and Aschochyta sp.