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In field crops the origin and movement of bacterial inoculum is difficult to determine due to inadequate means of distinguishing strains of bacteria. In this study the introduction, establishment, and spread of Xanthomonas campestris pv. dieffenbachiae (McCulloch and Pirone) Dye into anthurium fields were examined by monitoring the distribution of serologically distinct strains recovered from propagation benches and production fields. One thousand Anthurium andraeanum Lind. plants were indexed for X. c. pv. dieffenbachiae and 962 were later introduced into a production field. Strains recovered from the propagative stock were serotyped using a panel of 10 monoclonal antibodies and serotypes were compared to serotypes of strains already prevalent in the production field. Four distinct serotypes were identified which were not characteristic of strains already prevalent in the production field. Two biotypes of X. c. pv. dieffenbachia were also identified, based on their ability to hydrolyze starch. Sensitivity to 500 ppm streptomycin sulfate also was used to characterize strains associated with introduced propagative stock. Of 248 strains isolated from field plants, 39% were streptomycin resistant, whereas none of the strains isolated from introduced cuttings at the initial indexing were resistant. Over a 3-year period, strains with serotypes associated with the propagation material became established in the field, but spread to other cultivars was limited. This paper demonstrates the utility of serological methods for epidemiological studies.

Ralstonia solanacearum (Rs) race 4 strains cause bacterial wilt of edible ginger (Zingiber officinale). The survival of the pathogen was studied in plant-free soil and potting medium in the presence of plants inoculated by different methods (non-wounded, rhizome-wounded, and stem-wounded) and irrigated on different schedules (alternate and daily). Detection thresholds for Rs were determined for an enzyme-linked immunoabsorbent assay (ELISA), immunostrip assay, and polymerase chain reaction (PCR) using drainage water from soil and potting medium containing known concentrations of Rs. In the absence of a plant or in the presence of non-wounded plants, Rs populations declined rapidly in drainage water from potting medium during the first 9 days and were undetectable after 81 days. When plants were stem- or rhizome-wounded, Rs populations increased by two to three orders of magnitude from the initial population levels for the first 9 to 19 days and then gradually declined and became undetectable after 89 days. Results were similar in experiments with soil except for non-wounded ginger plants, where the initial decline in Rs populations was followed by an abrupt increase after day 11, reaching 7 log cfu/mL on day 21, then declining gradually to non-detectable levels after 137 days. The increase was attributed to natural infection of the plants followed by release of high populations of Rs into the irrigation water when plants wilted. When rhizome-inoculated plants were watered on alternate days, Rs was recovered from 97 to 129 days in soil and potting medium, but when the plants were watered daily, Rs was recovered in soil and potting medium up to 153 days after plant inoculation. ELISA using Ps1a monoclonal antibody detected the pathogen from >95% of the samples from soil and potting medium when viable populations were >5 log cfu/mL. The immunostrip assay (using the same antibody) detected the pathogen from 100% of the samples when viable populations were >3 log cfu/mL. PCR based on the flagellin gene fliC detected the pathogen from >95% of the samples from soil and from >74% of the samples from potting medium when viable populations were >4 log cfu/mL.

Fourteen species of ginger belonging to Zingiberaceae and Costaceae were evaluated for susceptibility to the bacterial wilt pathogen Ralstonia solanacearum (Rs) race 4 (ginger strains) by several methods of inoculation, including tests to simulate natural infection. Twelve of 14 species tested were highly susceptible to all strains of Rs race 4 upon stem inoculation, and susceptible plants wilted within 21 days. In contrast to previous reports that Rs strains from an invasive alien species, kahili ginger (Hedychium gardenarium), are nonpathogenic on ornamental gingers, the kahili ginger strain wilted both ornamental and edible ginger (Zingiber officinale) species within 21 days. Pour inoculation to the base of 11 plant species to simulate natural infection confirmed the ability of Rs to invade all the tested species without root wounds. Shampoo ginger (Zingiber zerumbet) was the most susceptible (wilted in 26 days) whereas pink ginger (Alpinia purpurata) and red ginger (A. purpurata) were the least susceptible and wilted in 71 and 76 days respectively. Pathogen survival in potting medium was evaluated by enumerating viable cells in effluent water from drenched pots with and without infected edible ginger after stem or rhizome inoculation. Ralstonia solanacearum survived in plant-free potting medium for 120 days and for 150 to 180 days in potting medium with infected edible ginger. The ability of Rs race 4 to infect many ginger species without wounding and to survive for long periods indicates that high risks will be incurred if the kahili ginger strain is inadvertently introduced from the forest reserves into ginger production areas.