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Physiology and Biochemistry

Papilla Formation in Corn Root-Cap Cells and Leaves Inoculated with Colletotrichum graminicola. R. T. Sherwood, Plant pathologist, U.S. Department of Agriculture, Agricultural Research Service, U.S. Regional Pasture Research Laboratory, University Park, PA 16802; Phytopathology 77:930-934. Accepted for publication 3 December 1986. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1987. DOI: 10.1094/Phyto-77-930.

Inoculation of single cells naturally sloughed from the root caps of corn seedlings may serve as a model system for studying pathogen-induced papilla formation. This approach circumvents the complicating influences of cohort cells in tissues or of chemical treatments used to obtain single cells. Seedlings were grown aseptically, and the outer calyptra cells that sloughed off were collected, washed, and plated on a medium consisting of glucose, inorganic salts, and agar. Conidia of Colletotrichum graminicola plated in the same place germinated and formed appressoria on the corn cells. Most appressoria produced penetration pegs, which penetrated directly without papilla formation, penetrated with papilla formation, or induced a papilla without penetration. The same events occurred in disks that were cut from mature leaves, inoculated, and floated on water. In root-cap cell and leaf disk inoculations, the ratio of unpenetrated papillae to penetrations without papillae was greater in dent corn lines than in sweet corn lines. Dent corn leaves formed fewer lesions per square centimeter than did sweet corn leaves inoculated at early tassel stage. When root-cap cells were inoculated, fewer penetrations occurred and more papillae formed in dent corn than in sweet corn. Application of a translational inhibitor, cycloheximide, inhibited papilla formation and enhanced penetration in root-cap cells and in leaf disks. Addition of 1% glucose or sucrose to the medium enhanced papilla formation and decreased penetration in root-cap cells or leaf disks. Thus, the responses of root-cap cells paralleled those of leaves to the regulatory influences of genotype, nutrition, and translational inhibition.