Formation of Haustoria and Granules on the Haustoria of the Downy Mildew Fungus, Peronospora parasitica, on Japanese Radish

Abstract

Haustorial formation of the downy mildew fungus, Peronospora parasitica was observed in the root tissues of susceptible and resistant cultivars of Japanese radish (Raphanus sativus horteinsis). The growth of hyphae in the susceptible cultivar was faster than that in the resistant cultivar. Five days after inoculation, haustoria were formed in the cells of the 63rd cell layer from the inoculated layer in the susceptible cultivar, and in the cells of the 12th cell layer in the resistant cultivar. The haustoria formed in both cultivars were similar in size and shape. On the surface of haustoria spherical or hemi-spherical granules, 1.7-3.7μm in diameter, were often observed in the susceptible cultivar, while rarely observed in the resistant. The granules were stained dark blue with sudan black B and red with sudan III, and disappeared after treatment with acetone. It was suggested, therefore, that the granules consisted of a kind of neutral lipid.