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Cytology and Histology

Suscept-Pathogen Relationship in Maize Affected by Yellow Leaf Blight. R. M. Jimenez-Diaz, Graduate Student, Department of Plant Pathology, Cornell University, Ithaca, NY 14853, Present address of senior author: Instituto Nacional de Investigaciones Agrarias, Centro Regional de Andalucia, Apdo 240, Cordoba, Spain; C. W. Boothroyd, Professor, Department of Plant Pathology, Cornell University, Ithaca, NY 14853. Phytopathology 66:1169-1173. Accepted for publication 20 April 1976. Copyright © 1976 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-66-1169.

Seedlings of maize were inoculated with conidia of Phyllosticta maydis, the imperfect stage of Mycosphaerella zeae-maydis. Over 90% of the conidia germinated within 12 hours, and produced one or two germ tubes. The germ tubes did not branch and were variable in length. Ingress occurred by direct penetration of an epidermal cell by a penetration peg which developed from an appressorium. Earliest penetration was observed 6 hours after inoculation, and 30% of the germinated conidia had given rise to penetration within 24 hours. Ingress was followed by the development of a bulbous to rod-shaped primary hypha. Secondary hyphae grew within epidermal cells and intercellularly in the mesophyll; they did not penetrate vascular tissue. Cytoplasmic granulations and discoloration and thickening of epidermal cell walls of penetrated cells prior to formation of primary hyphae were observed. Alterations in mesophyll cells and tissues in advance of the fungus were also observed. Nuclei in epidermal cells adjacent to the cell penetrated were positioned adjacent to the radial wall closest to the site of penetration.