Bioindicators for Ralstonia solanacearum race 4: plants in the Zingiberaceae and Costaceae families

Ralstonia solanacearum (Rs) race 4 causes bacterial wilt of edible ginger (Zingiber officinale) and limits crop production in the tropics. The use of bioindicator plants was investigated as a method for determining whether or not a field is contaminated with Rs race 4 before replanting with a susceptible crop. Tissue-cultured edible ginger (TCG), micro-sized red ginger (Alpinia purpurata; RG) and micro-sized spiral ginger (Costus barbatus; SG) were evaluated for suitability for detection of Rs race 4. Candidate hosts were planted into the infested medium, and Rs populations in plant tissues, potting medium and drainage water were evaluated by viable plate counts and Immunostrips using a species-specific monoclonal antibody. TCG wilted completely within an average of 9 days at the highest (log 8 cfu/mL) level of inoculum, and within 19 days at the lowest (log 4 cfu/mL) inoculum level. RG wilted in 17-26 and SG in 29-39 days. The final populations of Rs race 4 in wilted TCG tissues, potting medium and drainage water were between log 8.8-9.3 cfu/g, log 7.0-7.4 cfu/g and log 4.8-5.0 cfu/mL, respectively, regardless of the initial population levels. RG and SG did not enhance Rs population levels as well as TCG. On average, the bioindicator hosts increased the Rs populations by 100 to 1000-fold, thereby enabling detection with a simple immunodiagnostic test.