Genetic Diversity Among Mycoplasmalike Organisms Associated with Stone Fruit Diseases. U. Ahrens. Biologische Bundesanstalt für Land- und Forstwirtschaft, Institut für Pflanzenschutz im Obstbau, D-69216 Dossenheim, Germany. K.-H. Lorenz, and E. Seemüller. Biologische Bundesanstalt für Land- und Forstwirtschaft, Institut für Pflanzenschutz im Obstbau, D-69216 Dossenheim, Germany.. MPMI 6:686-691. Accepted 22 July 1993. Copyright 1993 The American Phytopathological Society.

Southern blot analysis was employed to examine genetic interrelatedness of mycoplasmalike organisms (MLOs) collected in Germany from peach, apricot, almond, Japanese plum, and flowering cherry trees showing yellowing and decline symptoms. Also, periwinkle-maintained MLOs obtained from stone fruits such as North American western X-disease MLO strains and southern European MLOs transmitted from trees affected by apricot chlorotic leaf roll, plum leptonecrosis, and Molières disease were included in this study. Randomly cloned chromosomal DNA fragments of apple proliferation and vaccinium witches'-broom MLOs and a ribosomal sequence of western X-disease MLO were used as probes. The results show that the German Prunus isolates form a homogeneous group that is closely related to apple proliferation MLO but distinctly different from the stone fruit isolates maintained in periwinkle. DNA of the periwinkle-maintained MLOs hybridized with probes from vaccinium witches'-broom MLO. Among these isolates, the X-disease MLOs showed similar patterns, whereas the southern European strains were different from one another and from the X-disease MLOs. The differences among the periwinkle-maintained isolates were confirmed by hybridization results obtained with the ribosomal probe.