VIEW ARTICLE

Ecology and Epidemiology

Nature of Suppression of Phytophthora capsici in a Hawaiian Soil. W. H. Ko, Professor, Department of Plant Pathology, University of Hawaii, Beaumont Agricultural Research Center, Hilo 96720; K. A. Nishijima, research associate, Department of Plant Pathology, University of Hawaii, Beaumont Agricultural Research Center, Hilo 96720. Phytopathology 75:683-685. Accepted for publication 9 January 1985. Copyright 1985 The American Phytopathological Society. DOI: 10.1094/Phyto-75-683.

A forest soil from South Hilo District on the island of Hawaii suppressed germination of sporangia of Phytophthora capsici and also damping-off caused in tomato seedlings by the fungus. The soil was also strongly inhibitory to spore germination of Phytophthora palmivora, Mucor ramannianus, Calonectria crotalariae, and Penicillium frequentans, but it was not inhibitory to spore germination of Pythium splendens or Neurospora tetrasperma, or to sclerotium germination of Sclerotium rolfsii. The suppressive soil was fungitoxic to sporangia of P. capsici and the germination inhibition by the soil was not affected by addition of nutrients. Although low pH was inhibitory to P. capsici, it alone could not account for the strong inhibitory effect of the suppressive soil. The inhibitory effect was not changed by autoclaving, ignition at 500 C for 16 hr, or H₂O₂ treatment. The inhibitory factor was neither water soluble nor diffusible. The suppression was not affected by amendment of soil with chelating agents. The clay, silt and sand fractions of the suppressive soil were all inhibitory to P. capsici. Results suggest that inorganic soil particles are responsible for the inhibition of germination of sporangia of P. capsici in the South Hilo soil.