DIFFERENTIATION OF VIRESCENCE MLOS USING WESTERN ASTER YELLOWS MYCOPLASMA-LIKE ORGANISM CHROMOSOMAL DNA PROBES AND RESTRICTION-FRAGMENT-LENGTH-POLYMORPHISM ANALYSIS

Two chromosomal fragments of the severe strain (SAY) of the western aster yellows mycoplasma-like organism (MLO) were cloned in Escherichia coli. These fragments were used to probe Southern blots of DNA extracted from plants infected with geographically and pathologically diverse MLOs. The two SAY probes hybridized with some, but not all, of the virescence-inducing MLOs examined, indicating that some of these MLOs are genetically related. Comparisons of restriction fragment length polymorphisms of MLO DNA established additional relationships within this group. The SAY-MLO probes did not hybridize with decline-inducing MLOs, plant pathogenic spiroplasmas, or healthy plants.