Distribution of Mycoplasma-like Organism and Ultrastructural Changes in Host Cells in Witches' Broom Diseased Sweet Potato and Morning Glory

Healthy sweet potato and morning glory plants were inoculated by feeding with infective leafhoppers, Orosius ryukyuensis, on each plant. The infected plants were examined by electron microscope. In the sweet potato plants, no mycoplasma-like organism (MLO) was observed before the appearance of initial symptoms, but as soon as the initial symptoms appeared, many branched filamentous form and bacilliform MLO were observed. In the phloem cells of sweet potato and morning glory plants which showed typical symptoms, numerous MLO ranging between 75 to 1, 400mμ in size were observed. In the morphology and distribution of MLO, there was no difference between both hosts. There appeared to be some differences in the morphology of MLO found in different plant parts: leaf vein, pedicel, stem, petal, and root. In mature phloem cells, MLO were often found crowded along the cell membrane. In immature phloem cells adjacent to apical meristem of stem, and petal, possible reproductive forms of MLO were observed in the cytoplasm. MLO were frequently found within sieve pores, suggesting that MLO might move through these pores. In the phloem cells of diseased plants, numerous large multivesicular bodies were frequently observed. In the vacuoles of these cells, high density of the square crystals varying in size from 0.1 to 2μ were also frequently observed.