PHYSICAL MAP OF THE WESTERN X-DISEASE PHYTOPLASMA CHROMOSOME

A physical map of the chromosome of the western X-disease phytoplasma was constructed and represents the first physical map of a phytoplasma chromosome. The western X-disease phytoplasma is a nonculturable, pla nt-pathogenic member of the class Mollicutes and is the causal agent o f a severe disease of fruit trees in North America. The map was genera ted by performing restriction digests of the chromosome and resolving the restriction fragments by pulsed-field gel electrophoresis. Souther n blot analysis using cloned phytoplasma probes confirmed the arrangem ent of contiguous restriction fragments. The locations of 20 restricti on sites for the enzymes Sal/I, XhoI, BssHII, RsrII, SmaI, and NotI we re mapped on the chromosome, which is circular and comprises approxima tely 670 kb. The locations of the two rRNA operons and of four previou sly cloned fragments of chromosomal DNA were also placed on the map.