Biochemical diversity profiling of Ralstonia solanacearum (L.) isolates causing bacterial rhizome rot of ginger (Zingiber officinale Rosc.) under in vitro conditions

Abstract

Ginger (Zingiber officinale Rosc.) is a commercially important spice and medicinal crop and it is affected by serious bacterial rhizome rot disease caused by Ralstonia solanacearum (L.). The present investigation was undertaken for biochemical characterization of ten isolates of R. solanacearum inducing bacterial rhizome rot of Ginger which collected from different locations under in-vitro experiments. Isolates were selected based on morphological, cultural, and biochemical properties and pathogenicity. For these evaluations, all isolates were grown on TZC medium and maintained at 28±2 °C for a period of 48-72 hr. Various biochemical tests such as acid production from various sources of carbohydrates, starch hydrolysis, Gelatin liquefaction, catalase production, urease activity, hydrogen sulphide production, gas formation, KOH solubility and Grams staining tests were conducted to evaluate the biochemical diversity and metabolic activity of R. solanacearum. In acid production test, all isolates showed gradual increase over time by change in color if medium. Dextrose and sucrose found suitable acid production than maltose. In starch hydrolysis test out of ten isolates, eight isolates are able to hydrolase the starch by showing zone formation. Hydrogen sulphide test revealed that, as the time increases few isolates are able to produce strong positive reaction. In gelatin liquefaction test, at early stage all isolate unable to show the gelatinase activity and after 78 hr few isolates showed strong enzymatic activity. In gas production test, none of the isolates showed positive reaction in 24hr, however after 72 hr all isolates demonstrated gas production except control. In urease production test, some isolates form the pink colour in broth media after 48hr and all isolates showed positive reaction after 78hr by producing ammonia. During grams staining reaction all the isolates showed negative reaction due to thin peptidoglycan layer unable to retain the stain. The formation of slime threads occurs due to the release of cellular DNA upon lysis of Gram-negative bacterial cells in the presence of 3% KOH solution. Catalase test was positive for all the isolates except RS-4. The study aids to contribute baseline data for accurate identification, comparison with known strains, and to support future molecular and epidemiological studies for effective management of bacterial wilt in Ginger.