GENETIC-ANALYSIS OF CLAVIBACTER-TOXICUS, THE AGENT OF ANNUAL RYEGRASSTOXICITY

Multilocus enzyme electrophoresis was used to examine the relatedness of 52 isolates of Clavibacter toxicus, the agent of annual ryegrass to xicity. These included 37 Western Australian (WA) field isolates sampl ed in 3 distinct locations over a 2-year period, and 15 isolates sampl ed from 6 different host plant species in 3 states in Australia over a pproximately 8 years. Seventeen reference strains for the related gene ra Curtobacterium, Rhodococcus and Arthrobacter were examined for comp arison. The 69 isolates were divided into 29 electrophoretic types (ET s), separated by genetic distances of 0.06 to 0.81. The C. toxicus iso lates fell into 12 ETs, 11 of which formed a tightly clustered group s eparated by a genetic distance of 0.23 or less. Thirty-one of the WA f ield isolates of C. toxicus fell into a single ET, and four into anoth er ET. Clavibacter toxicus therefore formed a closely related group wh ich was genetically distinct from the other plant pathogenic species, and a dominant widely disseminated strain of the species was identifie d in WA.