GENETIC RELATEDNESS BETWEEN 2 NONCULTURABLE MYCOPLASMALIKE ORGANISMS REVEALED BY NUCLEIC-ACID HYBRIDIZATION AND POLYMERASE CHAIN-REACTION

Dot-blot hybridization, using nine recombinant plasmids containing clover proliferation (CP) mycoplasmalike organism (MLO) DNA segments, showed that the cloned CP MLO-specific DNA probes hybridized with DNA isolated from CP MLO and potato witches-broom (PWB) MLO-infected periwinkle plants, but not with DNA extracted from healthy periwinkle plants nor from those infected by MLOs associated with clover phyllody (CPD), hydrangea virescence (HV), eastern aster yellows (EAY), and western aster yellows (AY27). Very similar restriction fragment length polymorphism (RFLP) of CP and PWB MLO chromosomal DNA was observed by Southern-blot hybridization using four different CP MLO DNA probes. Similar DNA fragments were amplified when DNAs from CP or PWB MLO-infected plants were used as PCR templates, whereas no DNA fragments were amplified when DNAs from healthy CPD, HV, EAY, and AY27 MLO-infected plants were used as polymerase chain reaction templates. These results suggested that CP and PWB MLO isolates are genetically related, yet distinct from CPD, HV, EAY, and AY27 MLO isolates.