CHROMOSOMAL HETEROGENEITY AMONG VARIOUS STRAINS OF SPIROPLASMA-CITRI

The genomes of various Spiroplasma citri strains were digested with se veral restriction enzymes, and the fragments were analyzed by pulsed-f ield gel electrophoresis. Polymorphism of the restriction patterns was observed. The genome sizes of the strains obtained when we added the restriction fragment sizes ranged from 1,650 to 1,910 kbp. Physical an d genetic maps of 12 strains were constructed by using several DNA pro bes as genetic markers. The relative positions of mapped loci were con served in most of the strains; the main differences were differences i n the order and number of restriction sites and differences in the siz es of certain fragments. The distribution of viral sequences, which oc cur at multiple sites in the S. citri genome and are homologous to the sequences of S. citri virus SpV1 strains R8A2B and S102, was also stu died.