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Histological Reactions and Effects on Position of Epidermal Nuclei in Susceptible and Resistant Corn Inoculated with Helminthosporium maydis Race T. M. R. Contreras, Graduate Student, Department of Plant Pathology, Cornell University, Ithaca, N.Y. 14853; C. W. Boothroyd, Professor, Department of Plant Pathology, Cornell University, Ithaca, N.Y. 14853. Phytopathology 65:1075-1078. Accepted for publication 22 April 1975. DOI: 10.1094/Phyto-65-1075.

The first detectable manifestation of differential host response in susceptible (W64Atcms and M017tcms) and resistant (W64A and M017) corn seedlings inoculated with Helminthosporium maydis (Cochliobolus heterostrophus) race T was an affect on the position of epidermal nuclei in the incompatible reaction. The nuclei in epidermal cells surrounding the penetration site were positioned next to the radial walls most proximal to the penetrated cell. This event occurred simultaneously with penetration and formation of a primary hypha 6-9 hours after inoculation. Results of inoculations with H. carbonum (a nonpathogen of these inbreds) and H. victoriae (a nonpathogen of corn) suggest that the phenomenon may be associated with incompatible corn-fungus interactions. Hyphal growth of the pathogen in resistant corn was arrested about 12 hours after inoculation, and had apparently ceased by 18-24 hours. The pathogen colonized susceptible tissue readily, with changes in the morphology of the infected tissue occurring later than in the incompatible reaction. It is suggested that differential disease reaction is determined very early after penetration.

Additional keywords: southern corn leaf blight.