[Ultrastructures of a mycoplasma-like organism causing mulberry dwarf disease]

The pathogen causing the dwarf disease of mulberry in Tongxiang, Zhejiang Province was investigated based on transmission electronic microscopy of the leaf vein of diseased plants collected in the field. A mycoplasma-like organism was identified in the sieve tube, companion, and parenchyma cells of the phloem tissues infected. The organism was spheric or oval in shape, ranging from 50 nm to 160 nm in diameter, and with bilamina unit membrane of 8-10 nm in thickness, and was filled with nuclear strands or fibrous material. Some nuclei of mesophyll cells in the diseased leaves were found disrupted as their nuclear membrane was broken, followed by of nucleo-cytoplasmic matrix and dispersive disappearance of nucleoli. Furthermore, other ultrastructural aberration including depletion of chloroplast stroma, disruption of chloroplast grana, increase of mitochondria and rough endoplasmic reticulum, and discomposition of some mitochondrial cristae were also observed associated with the pathological changes caused by the mycoplasma-like organism. In contrast, this type of organism was not found in healthy plants examined. Thus, the mycoplasma-like organism is likely to be a pathogen attributable to the mulberry dwarf disease.