Transmission frequency of Clavibacter michiganensis subsp. insidiosus to lucerne seeds
A PCR-based method (isolation from plant material on semi-selective medium followed by PCR) which has been developed for Clavibacter michiganensis subsp. insidiosus (EPPO A2 quarantine pest) was used in USA to determine the frequency of transmission of the bacterium to lucerne seeds. To obtain infected seed lots, seeds were produced in three different ways: 1) from infected plants grown and pollinated in the glasshouse; 2) from infected plants grown in the field and transplanted into the glasshouse to produce seeds; 3) from diseased 2-year-old plants grown and pollinated in the field. Seeds produced by each infected plant were collected and tested to identify infected seed lots. It was found that 6.3 to 7.7 % of diseased plants had transmitted C. m. subsp. insidiosus to seeds. When individual seeds were tested in infected seed lots, it was found that approximately 2.5 to 8.7 % of the seeds contained the bacterium. The authors concluded that transmission of C. m. subsp. insidiosus from infected plants to seeds occurred at a low frequency with a few infected plants producing a limited number of infected seeds. They also felt that this PCR-based method could be particularly useful in identifying the bacteria isolated from lucerne seed lots.
Sources
Samac, D.A.; Nix, R.J.; Oleson, A.E. (1998) Transmission frequency of Clavibacter michiganensis subsp. insidiosus to alfalfa seed and identification of the bacterium by PCR.
Plant Disease, 82(12), 1362-1367