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Histopathology of Resistant and Susceptible Soybean Hypocotyls Inoculated with Phytophthora megasperma var. sojae. W. L. Klarman, Department of Botany, University of Maryland, College Park, Maryland 20742; M. K. Corbett, Department of Botany, University of Maryland, College Park, Maryland 20742. Phytopathology 64:971-975. Accepted for publication 7 February 1974. DOI: 10.1094/Phyto-64-971.

Hypocotyls of resistant and susceptible soybean plants were examined by light and electron microscopy 3 days after inoculation with Phytophthora megasperma var. sojae. All tissues of susceptible hypocotyls were ramified by both inter- and intracellular hyphae of the pathogen. Parenchyma near the site of infection was completely disorganized, but vascular tissues and cells with secondary walls remained intact even when heavily infected. In inoculated hypocotyls of resistant plants only those cells directly surrounding the inoculation wound were colonized by the pathogen, and normal appearing organelles were present in adjacent noninfected host cells. Some host cells close to the infected area were filled with granular, dark-staining cytoplasm which appeared to form a barrier to further movement of the fungus.