NATURE AND GENETIC RELATEDNESS OF THE MYCOPLASMA-LIKE ORGANISM CAUSING RUBUS STUNT IN EUROPE

Cultivated red raspberries (Rubus idaeus), and wild blackberries (R. fruticosus, R. caesius, and Rubus hybrids) showing symptoms of rubus stunt were collected in Germany, France, and Italy. Ribosomal DNA of the mycoplasma-like organism (MLO) that causes rubus stunt was amplified by a polymerase chain reaction procedure and then digested with AluI and RsaI restriction endonucleases. All samples examined showed the same restriction profiles, which were similar to those of the MLOs inducing elm yellows and alder yellows. However, the rubus stunt MLO could be distinguished from the elm and alder MLOs by Southern blot analysis using DNA probes from a strain of the elm yellows MLO. A variability of the hybridization profiles, probably caused by restriction fragment length polymorphisms, was observed among the rubus stunt samples. From both rDNA restriction site and Southern blot analyses it can be concluded that the rubus stunt agent and the elm yellows and alder yellows MLOs an not identical but closely related and can be grouped in the same taxonomic cluster.