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Symptomatology, Etiology, and Histopathology of Botrytis Brown Stain of Onion. C. A. Clark, Graduate Assistant, Department of Plant Pathology, New York State College of Agriculture and Life Sciences, Cornell University, Ithaca, New York 14850; J. W. Lorbeer, Professor, Department of Plant Pathology, New York State College of Agriculture and Life Sciences, Cornell University, Ithaca, New York 14850. Phytopathology 63:1231-1235. Accepted for publication 21 March 1973. DOI: 10.1094/Phyto-63-1231.

Botrytis cinerea was isolated with consistency from dry outer scales of onion bulbs displaying brown stain symptoms. Proof that B. cinerea was the causal organism of the disease was obtained by inoculation of healthy onion bulbs, brown stain symptom development, and subsequent reisolation of the fungus from the areas with symptoms. Several methods of inoculation and the symptoms induced are described. Spots produced on artificially inoculated dry scales were limited in size and remained physically intact. Fleshy scales were actively macerated prior to a general discoloration of the entire scale. In naturally infected dry scales, the pathogen grew intercellularly with little visible damage to tissue structure. Hyphae were far more abundant in the mesophyll parenchyma than in other tissues of the bulb scale. Sclerotia were produced in the abaxial epidermis.