MYCOPLASMA-LIKE ORGANISMS ASSOCIATED WITH A GRAPEVINE YELLOWS DISEASEOCCURRING IN ITALY

Transmission electron microscopy of tissues from Vitis vinifera L. pla nts, naturally infected with a yellows disease similar to flavescence doree (FD), revealed the presence of pleomorphic mycoplasma-like organ isms (MLOs). These occurred in varying concentrations in mature sieve tube elements of leaf veins. Generally the concentration was very low, although large populations of MLOs were found colonizing almost the e ntire lumen of two cells. The micro-organisms varied considerably in s ize, shape and electron opacity. Spherical, oval and filamentous forms were recognized. The bodies showed the typical ultrastructural detail s of other known plant pathogenic MLOs. They were bounded by a smooth trilaminar membrane and contained ribosome-like granules and DNA-like strands.