|Samac, Deborah - Debby|
Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/21/1998
Publication Date: N/A
Interpretive Summary: Bacteria that cause plant diseases can be spread between plants and between locations in a number of ways. Some bacteria are able to invade the seeds of plants and can be carried with the seeds to new locations. In cases where the frequency of seed infection is high, seed health may need to be tested and infected seed lots discarded to limit the spread of the disease. .Only a few diseases of alfalfa are reported to be seed-borne. One of thes diseases, bacterial wilt of alfalfa, has been reported to be transmitted in seed, but the frequency of seed infection is not known. A test was developed to identify the bacterium causing the disease and was used to measure the frequency of seed infection. For the test, alfalfa seed are ground and suspended in a nutrient broth. The broth is diluted and used to inoculate agar plates. Bacterial colonies growing on the plates are identified using a rapid and specific test based on amplifying a diagnostic cpart of the bacterial DNA. Alfalfa plants were grown and infected with th bacterium and seeds produced from infected plants. Only 6.25 to 7.7% of diseased plants transmitted the bacterium to seed. From these plants, 2.5 to 8.7% of seeds contained the bacterium. Considering all infected plants, the rate of seed transmission was low, approximately 0.13%. Diseased plants produced fewer seed than healthy plants. Seed produced in fields where the frequency of diseased plants is low should have very low numbers of infected seed. The test could be used to assess health of alfalfa seed lots. The rates of seed infection will be of interest to seed producers as well as regulators concerned with seed health issues.
Technical Abstract: A sensitive PCR-based identification method was developed that is rapid and specific for Clavibacter michiganensis subsp. insidiosus, the causal agent of alfalfa bacterial wilt. The assay was used to identify the bacterium isolated on a semi-selective medium from infected alfalfa plants. Seed was produced from plants grown and pollinated in the greenhouse, diseased plants grown in the field and transplanted to the greenhouse to produce seed, and diseased 2-year-old field-grown plants. Seed were ground and the seed slurry plated to identify infected seed lots. From 6.25 to 7.7% of infected plants transmitted C. m. subsp. insidiosus to seed. In assays in which individual seeds were analyzed from infected seed lots, 2.5 to 8.7% of seeds contained the bacterium.