New host plants for Ralstonia solanacearum from India

Abstract

Ralstonia solanacearum can cause serious losses on many economically important crops. Here, two new hosts, davana (Artemisia pallens) and coleus (Coleus forskohlii) are reported for R. solanacearum. Both are important crops in medicinal and aromatic industries in India. Coleus and davana plants showing typical wilt symptoms were found and a tentative diagnosis of R. solanacearum was made as a result of oozing from cut stems placed in water. After isolation from both hosts, morphological studies revealed that bacterial isolates were Gram-negative rod-shaped, non-capsulated and non-spore forming. Isolates grown on SMSA medium (Engelbrecht, 1994) were highly fluidal, white-coloured with a light pink centre and bluish margin and round to irregular shape, typical of R. solanacearum. Electron microscopic studies revealed that bacterium was rod-shaped with one to four polar flagella (Hayward, 1964). PCR amplification using the OLI 1 and Y2 primers (Seal et al., 1993) gave a 292 bp product with strains from both hosts. A positive result was also obtained using a serological diagnostic kit obtained from the International Potato Research Center, Lima, Peru (Priou et al., 1999). A positive reaction with single chain variable fragment (SCFV) antibody specific to R. solanacearum further supported the identification. The isolates produced typical wilt symptoms on their respective hosts within 5–6 weeks after inoculation using root injury. Thus, based on morphology, biochemical and nutritional tests and pathogenicity, including ability to cause wilt on solanaceous and non-solanaceous crops, the two isolates were identified as R. solanacearum biovar-III (Hayward, 1964). Identification of R. solanacearum is further supported by PCR and serological identification. This is the first record of R. solanacearum causing bacterial wilt of davana and coleus in India. This study was supported by a grant from the NATP-CGP under the project, ‘Molecular approaches for detection of Ralstonia solanacearum’. The authors would like to thank Dr. R. D. Rawal and Dr. M. Krishna Reddy for electron microscope studies and suggestions.