Genomic variation in Clavibacter michiganensis subsp. michiganensis provides a new understanding of bacterial canker of tomato. C. M. MEDINA-MORA (1), N. Werner (1), J. Bell (1), M. Hausbeck (1), F. J. de Bruijn (2), and D. W. Fulbright (1). (1) Dept. Botany and Plant Pathology; (2) PRL- DOE, Michigan State University, East Lansing, MI 48824. Phytopathology 89:S52. Publication no. P-1999- 0369-AMA.

Polymerase chain reaction protocols (rep-PCR) using REP, ERIC, and BOX primers resolved five different genotypes of Clavibacter michiganensis subsp. michiganensis. A fourth primer, (GTG)5 revealed further genetic variability and divided each of the genotypes into subgroups. For example, the absence of polymorphic bands in BOX fingerprint type A strain suggested that this group is of low genetic diversity. However, cluster analysis of combined (GTG)5- and BOX-PCR fingerprint patterns of type A revealed 3 subgroups among these isolates. Variability observed with (GTG)5 has also been useful in determining whether or not specific isolates are found in the same location over time. For example, BOX- PCR fingerprint type D has only been found in two locations in Michigan. Cluster analysis of combined (GTG)5- and BOX-PCR fingerprint patterns has indicated that new subgroups of D type genotype are found each year in these locations, potentially indicating that new introductions are made each year.