In maize leaves experimentally infected with various isolates or strains of maize chlorotic dwarf virus, including a newly characterized strain (M1), and in naturally infected johnsongrass, only two types of cytoplasmic inclusions were consistently observed: (i) quasi-spherical electron-dense granular inclusions, and (ii) curved or straight bundles of fibrous inclusions. Both types were detected by light and (or) electron microscopy in vascular parenchyma and phloem cells, and less frequently in bundle-sheath and adjacent mesophyll cells. The dense granular inclusions usually contained numerous isometric virus-like particles, some of which may have been released into the surrounding cytoplasm. However, a high proportion of these inclusions in cells infected with the mild type strain and a type-like isolate (M8) were either devoid of or contained very few viruslike particles. In maize leaves infected with the white stripe (WS) isolate, the chloroplasts were markedly deformed; in leaves of stunted plants doubly infected with M8 and the serologically distinct M1 strain, some phloem cells appeared degenerated. Electron microscopy of preparations of purified M1 stained with uranyl acetate revealed both stain-impenetrable full particles and stain-penetrable empty or partially empty particles. Both full and apparently empty particles were also found in cells of maize leaves infected with M1, whereas with other strains and isolates, mainly full particles were found both in situ and in vitro. Key words: maize chlorotic dwarf virus, cytopathology, ultrastructure, maize, johnsongrass.
Genomic of the severe isolate of Maize chlorotic dwarf virus
