Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 8/16/1999
Publication Date: N/A
Technical Abstract: Clavibacter michiganensis subsp. insidiosus (Cmi) causes bacterial wilt of alfalfa and is found in most alfalfa-growing areas in North America. Bacteria multiply in xylem vessels and cause wilting, stunting, and yellowing although symptoms may not be evident until the second or third year after infection. Bacteria persist for years in dried plant material and can be recovered from seed obtained from diseased plants. In pure culture, Cmi grows slowly as fluidal pale yellow colonies that often develop a dark blue pigment. However, non-fluidal and non-pigmented pathogenic isolates can be recovered from diseased plants and epiphytic bacteria with similar colony characteristics are often associated with alfalfa seed. A PCR assay, based on amplification of a multicopy insertion element from bacteria added directly to the reaction, was developed to identify Cmi isolated from plants and seed. Seed obtained from diseased plants were tested for the presence of Cmi by grinding and plating seed on a semi-selective agar medium. Only 6.3 to 7.7% of diseased plants transmitted Cmi to seed. In seed lots from these plants, 2.5 to 8.7% of seeds contained Cmi. PCR assays using seed grindate were not successful in detecting the bacterium.