Agriculture Reference
In-Depth Information
Figure 10.9. Corn plants infected with Clavibacter michiganense subsp. Nebraskense , the cause of Goss's
wilt of corn, that had been transmitted by the planted seed (courtesy of Johnson Family Farms).
Indicator Tests
Extracts of seeds may be used to inoculate healthy seedlings or mature plants. If symptoms develop on the
inoculated plants this would indicate the presence of the pathogen in the seed (Fig. 10.10). This type of test
is useful for bacteria and viruses. However, as with grow- out tests, symptoms must be very distinct to allow
for accurate identiication of the target pathogen. The procedure also may take considerable time, space,
and labor.
Phage-Plaque
Phage-plaque procedures utilizes viruses (phages) that speciically cause lysis of particular bacterial species.
Spore suspensions of the suspect bacteria are seeded into agar, and the test phage layered over the top of
the solidiied agar. If the target bacteria is present, colonies become lysed and develop plaques that can then
be counted (Fig. 10.11). The technique has been used for several important seedborne bacteria. However,
it requires a thorough knowledge of the pathogen, and other microorganisms involved. Sensitivity also can
be reduced by the presence of saprophytes.
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