A GENOTYPE-BASED SYSTEM FOR IDENTIFICATION AND CLASSIFICATION OF MYCOPLASMALIKE ORGANISMS (MLOS) IN THE ASTER YELLOWS MLO STRAIN CLUSTER

Fifteen mycoplasmalike organism (MLO) strains from North America and Europe, including aster yellows (AY), tomato big bud (BB), clover phyllody(CPh), chrysanthemum yellows (CY), and unknown MLOs, were studied. These MLOs are among those previously identified, on the basis of dot hybridizations, as members of the AY MLO strain cluster. Restriction fragment length polymorphism (RFLP) analyses revealed that all 15 strains can be classified into three genomic types: type I (typified by eastern AY MLOs), type II (e.g., western AY and CY MLOs), and type III (e.g., CPh MLO). Four key DNA probes (pAY9N, pBB88, pBB101, and pCN1-25) were designated for use in RFLP analyses for the identification of strains in the AY MLO strain cluster and the differentiation of the types within this cluster. This classification is consistent with results from monoclonal antibody typing and polymerase chain reaction analysis, but not with classifications based solely on biological properties.