Studies on Taxonomic Relationships of Mycoplasma–like Organisms by Southern blot Analysis

Chromosomal DNA fragments from the mycoplasma-like organisms (MLOs) associated with American aster yellows, apple proliferation, clover phyllody, and vaccinium witches' broom were cloned. Several MLO-specific fragments from each of these four isolates and a sequence from the 16S rRNA gene of an aster yellows MLO were used in Southern blot hybridizations to investigate the taxonomic relationships of 26 pathologically and geographically diverse MLOs. These MLOs were divided into four categories according to the symptoms induced in periwinkle. Genotypically, these isolates represented four groups (16S RFLP groups) of a classification based on restriction fragment length polymorphisms (RFLP) and sequencing data of the 16S rRNA gene. Probes from three isolates of one symptom category hybridized with isolates from all symptom categories. This result indicates that classification of MLOs by symptomatology does often not coincide with genetic relationships. The hybridization results confirmed the findings, of the 16S RFLP classification that most MLOs from herbaceous plants, especially those inducing virescence in periwinkle, are interrelated. These isolates, which were assigned to one 16S RFLP group, could be further differentiated in this study. Itcould be shown that aster yellows, clover phyllody, stolbur, and safflower phyllody and sandal spike are caused by distinct MLOs. The MLOs associated with apple proliferation, vaccinium witches' broom, and witches' broom of lime as well as two isolatesfrom, stone fruits could also be recognized as distinct organisms.