VIEW ARTICLE

Cytology and Histology

Distribution and Ultrastructure of Peronosclerospora maydis in Maize Shoot Tips. K. Takahashi, Plant pathologist, Division of Plant Pathology, National Institute of Agricultural Sciences, Yatabe, Tsukuba, Ibaraki 305, Japan; T. Inaba(2), and T. Kajiwara(3). (2)Plant pathologist, Division of Plant Pathology, National Institute of Agricultural Sciences, Yatabe, Tsukuba, Ibaraki 305, Japan; (3)Plant pathologist, Tropical Agriculture Research Center, Yatabe, Ibaraki 305, Japan. Phytopathology 71:1133-1137. Accepted for publication 20 January 1981. Copyright 1981 The American Phytopathological Society. DOI: 10.1094/Phyto-71-1133.

The ultrastructure of maize (Zea mays) shoot tips, either uninfected or infected with Peronosclerospora maydis (the maize downy mildew pathogen), was studied in relation to the systemic infection. Hyphae and haustoria were found in almost every portion of the tip, including the apical meristem, subapical meristem, initial leaf primordium, and leaf primordium. However, hyphae were never observed in the single-cell-thick mantle layer, or the top part of the subapical meristem (25 μm from the top). Degeneration of host cells in the shoot tip of infected plants was seldom encountered and degeneration of proplastids was not observed. All the hyphae and haustoria found in the shoot tip appeared to have been alive and vigorous at fixation, as judged by the ultrastructural appearance of their organelles. The fungus in the apical meristem is considered to extend hyphae and penetrate into the leaf primordium concurrently with shoot tip growth. The ultrastructure of the fungus and host-parasite interface in the shoot tip was similar to that in other downy mildews already reported.