ASSOCIATION, DEVELOPMENT, AND GROWTH CYCLE OF MYCOPLASMA-LIKE ORGANISMS IN PLANTS AFFECTED WITH CLOVER PHYLLODY

Examination of ultrathin sections of various parts of clover phyllody-affected aster plants (Callistephus chinensis Nees) by electron microscopy revealed the presence of pleomorphic bodies which resembled Mycoplasma species. These Mycoplasma-like organisms (MLO), ranging between 75 and 1100 mμ in size (diameter or maximum length), were found in varying concentration in the sieve elements of vascular tissues of roots, stems, leaves, pedicels, and foliaceous structures of phylloid flowers. MLO were also observed in the sieve elements of leaves of affected barley (Hordeum vulgare L.) plants-a monocotyledonous host of the disease-but not in healthy aster or barley plants. In some sieve elements, MLO were found concentrated along the cell wall with their extrusions inside the sieve pores, suggesting that cell-to-cell movement of the organism might take place through these pores. Four forms of MLO were recognized on the basis of their size, shape, and internal structure. All forms had a single unit membrane and contained ribosome-like granules. These forms are considered to represent the developmental stages in the growth cycle of MLO in vivo. © 1969.