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Host Isolate Interactions in Corn Inbreds Inoculated with Cochliobolus carbonum Race 3. A. H. Hamid, Graduate student, Department of Plant Pathology, Regional Research Laboratory, USDA, ARS, The Pennsylvania State University, University Park 16802, Present address: Malaysian Agricultural Research and Development Institute (MARDI) Serdang, Selangor, Malaysia; J. E. Ayers(2), and R. R. Hill, Jr.(3). (2)Professor, Department of Plant Pathology, Regional Research Laboratory, USDA, ARS, The Pennsylvania State University, University Park 16802; (3)Research agronomist, Regional Research Laboratory, USDA, ARS, The Pennsylvania State University, University Park 16802. Phytopathology 72:1169-1173. Accepted for publication 21 January 1982. 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, 1982.. DOI: 10.1094/Phyto-72-1169.

Nine Corn (Zea mays) inbred lines were examined after inoculation with isolates of Cochliobolus carbonum race 3 (= Helminthosporium carbonum) differing in levels of virulence. Reaction was measured by determining the effects of the lines on three components of parasitic fitness: disease efficiency, lesion length, and sporulation capacity. Differences among host genotypes were significant when tested against the six isolates. Similarly, isolates differed significantly in their degree of virulence on the host lines. Host isolate interactions for the three fitness traits were significant suggesting that isolates responded differently to different hosts. Regression analysis was used to determine the stability of resistance. An inbred line was defined as having stable resistance when it had a low mean disease rating, a regression coefficient near zero, and small deviation from regression. The large variation detected in this study suggested that stable resistance in corn lines to C. carbonum race 3 would not easily be found.

Additional keywords: genotype environment interactions, horizontal resistance, maize.