Da. Samac et al., TRANSMISSION FREQUENCY OF CLAVIBACTER-MICHIGANENSIS SUBSP INSIDIOSUS TO ALFALFA SEED AND IDENTIFICATION OF THE BACTERIUM BY PCR, Plant disease, 82(12), 1998, pp. 1362-1367
A sensitive polymerase chain reaction (PCR)-based identification metho
d was developed for Clavibacter michiganensis subsp. insidiosus, the c
ausal agent of alfalfa bacterial wilt. The method, which targets a hig
h-copy-number insertion element, is rapid and specific for this plant
pathogen. The assay was used to determine the frequency of transmissio
n of the pathogen to alfalfa seed. Seed was produced from infected pla
nts grown and pollinated in the greenhouse, from infected plants grown
in the field and transplanted to the greenhouse to produce seed, and
from diseased 2-year-old field-grown plants. Seed from each infected p
lant were assayed to identify infected seed lots. Seed were ground to
a fine powder and soaked in a liquid medium, after which a portion of
the seed slurry was plated on a semi-selective agar medium. The PCR as
say was used to identify C. michiganensis subsp. insidiosus colonies o
n plates. Approximately 6.3 to 7.7% of diseased plants transmitted C.
michiganensis subsp. insidiosus to seed. In assays in which individual
seed were analyzed from infected seed lots, approximately 2.5 to 8.7%
of seed contained the bacterium.