Diseases and Management of Crops under Protected Cultivation

(Diseases and Management of Crops under Protected Cultivation)
new genus Burkholideria. Later Yabuuchi et al., (1995) established the genus Ralstonia to
accommodate R. solanacearum, R. pickettii and R. eutropha. Gram negative, rod shaped,
measuring 0.5-0.7x1.5-2.5 µm, oxidase and catalase positive, accumulate poly-B-Hydroxy butyrate
(PHB) and reduce nitrate. Flagella are polar when present. No growth at 40 0 C, little or no growth in
broth with 2.0% NaCl. Negative for Arginine dihydrolase, gelatine liquefaction and starch or
esculine hydrolysis. Defensible brown pigment is produced on complex media. Two type of
colonies are observed on complex medium containing 0.5% glucose: fluidal (Mucoid) due to
production (EPS), where as other dry (butyrous) (Schaad et al., 2001).
4. Serological methods
In isolating bacteria, Ralstonia solanacearum colonies can be confused with saprophytic
colonies. Since it is very easy to examine cells from isolated colonies on the medium,
agglutination tests can be made and allow a more efficacious screening of the colonies.
Otherwise, agglutination tests can be used directly with exudates from several infected plants. In
this way, the bacterium can be directly detected in potato, tomato eggplant, sweet pepper and
banana. The most commonly used assays for bacteria detection and identification are
agglutination, enzyme-linked immunosorbent assay (ELISA), immunofluorescence (van der Wolf
et al., 2004), lateral flow strip tests or flow-through assays immunodiagnostic assays using R.
solanacerum specific. Antibodies (also known as immunoglobulins) are proteins that are used by
the immune system to identify and neutralize foreign objects, such as bacteria. Amore subtle
detection technique is immunofluorescence, which provides a means for detecting the bacterium
in the plant, water and soil. The IF technique can be also used in detecting the bacterium in the
host-plant and in studying the rate of spread of the pathogen
Serology techniques are relatively low-cost and easily performed tests for routine in situ
use. Immunoassays are being applied routinely for the detection of plant pathogens in plant
material and soil and tests such ELISA have demonstrated the sensitivity and specificity required
to replace time –consuming and expansive assays such as indicator-plant inoculation and dilution
plating. Serological techniques also have the advantage that immunoassays are well-established
technique s for detection and identification of bacterial species. However, for a rapid reasonably
sensitive, assays of total bacterial numbers of a particular species, immunoassays may be the
method of choice.
This serological assays so far the detection of pathogen were able to provide information
as to the presence or absence of the pathogen in soil and plant, however, they could not
discriminate between virulent and avirulent strains of the pathogen and are not specific to strain
and races. In this technique, virulent bacterial cells (encapsulated with mucin) from tomato seeds
are used as antigen and polyclonal antisera are developed in rabbit using a classified
immunization protocol. Antisera thus developed are examined for the antibodies titre, sensitivity,
specificity, rapidity and the efficacy of the antibody in identifying the potential for the application of
- 46 -