VIEW ARTICLE

Resistance

Single and Combined Effects of Monogenic and Polygenic Resistance on Certain Components of Northern Corn Leaf Blight Development. A. D. Raymundo, Former graduate research assistant, Department of Plant Pathology, University of Illinois, Urbana 61801, Present address of senior author: Plant Pathology Laboratory, Institute of Plant Breeding, University of the Philippines at Los Baņos, College, Laguna, Philippines 3720; A. L. Hooker, professor, Department of Plant Pathology, University of Illinois, Urbana 61801. Phytopathology 72:99-103. Accepted for publication 7 May 1981. Copyright 1982 The American Phytopathological Society. DOI: 10.1094/Phyto-72-99.

The dominant genes HtA, HtC, and HtD singly or in combination with high, intermediate, and low polygenic resistance were studied to determine their effects on incubation period, latent period, lesion size, infection efficiency, sporulation capacity, and infection rate of Helminthosporium turcicum causing northern corn leaf blight. Gene HtC restricted the enlargement of lesions significantly, regardless of genetic background. Gene HtD had the same effect, although not as marked as that of HtC except when the inbred background had a high polygenic resistance. Gene HtC was as effective as HtA in limiting lesion size in inbred backgrounds of high polygenic resistance. Lesion size restriction by gene HtA homozygous in Oh43 × B37 was not significantly different than when it was heterozygous in A632 × A619. In terms of infection rate, HtA homozygous in Oh43 × B37 was considerably more effective in inhibiting disease development than when it was heterozygous in A632 × A619. In terms of infection rate, HtC differed significantly from HtD in inbred backgrounds with moderate polygenic resistance, but not in backgrounds with high polygenic resistance. Genes HtC and HtD in combination with high polygenic resistance were as highly effective in limiting disease development as when homozygous HtA in Oh43 × B37. Gene HtC was better than gene HtD in suppressing sporulation when present in inbreds having intermediate polygenic resistance. Gene HtC was as effective as gene HtA in reducing sporulation.