RESTRICTION-FRAGMENT-LENGTH-POLYMORPHISMS WITHIN THE APPLE PROLIFERATION MYCOPLASMALIKE ORGANISM

Genetic homogeneity of the mycoplasmalike organisms (MLOs) associated with apple proliferation (AP) disease was examined by comparing sample s collected in south-western Germany, France, Italy, and Romania by So uthern blot analysis. The material examined consisted of two periwinkl e-maintained strains of the AP-MLO, samples from witches' brooms of 48 symptomatic trees, and root samples from 14 latently infected trees. Six cloned chromosomal DNA fragments of one of the periwinkle-maintain ed strains were used as probes. These probes, which were specific for the AP-MLO and other European fruit MLOs, hybridized with DNA of all s amples which indicates that the MLOs examined were closely related wit h one another. However, restriction fragment length polymorphism was o bserved among the samples. Four hybridization patterns occurred which were interrelated by common bands. Therefore, the AP agent can be rega rded as a taxonomic entity. The variability among the isolates seems n ot to be due to their geographical origin but might be related to path ological traits.