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Differential Inhibitory Activity of a Corn Extract to Erwinia spp. Causing Soft Rot. John R. Hartman, Assistant Professor, Department of Plant Pathology, University of Kentucky, Lexington 40506; Arthur Kelman(2), and C. D. Upper(3). (2)(3)Professor, Department of Plant Pathology, and Research Biochemist, Agricultural Research Service, U.S. Department of Agriculture, Department of Plant Pathology, University of Wisconsin, Madison 53706. Phytopathology 65:1082-1088. Accepted for publication 26 April 1975. DOI: 10.1094/Phyto-65-1082.

A water-soluble fraction extracted from corn leaves and stalks was more inhibitory to soft rot bacteria (Erwinia spp.) that are nonpathogenic to corn than to the bacterial corn stalk rot pathogen (ECZ), which is a pathotype of E. chrysanthemi. Concentrations of the differentially inhibitory fraction (DIF) greater than 0.75 grams equivalent fresh weight of plant tissue extracted per milliliter of culture medium killed E. carotovora (EC 208) in broth within 20 hours, whereas ECZ isolates were not killed at this concentration. Other corn pathogens such as P. syringae, and Erwinia stewartii were less susceptible to the inhibitory fraction than were various Erwinia isolates and several other phytopathogenic bacteria nonpathogenic to corn. DIF prepared by thawing of frozen crushed corn tissue in boiling water prior to extraction had low inhibitory activity. DIF preparations from several different corn lines were each active. Activity was higher in DIF extracts from whorl tissues than from an equal weight of leaf or stalk sheath tissue.