Small cardamom (Elettaria cardamomum Maton.) and ginger (Zingiber officinale Roxb) bacterial wilt is caused by same strain of Ralstonia solanacearum: a result revealed by multilocus sequence typing (MLST)

Abstract

Bacterial wilt in cardamom (Elettaria cardamomum Maton) was observed in Kerala state of India. Infected plants showed wilting wherein all leaves roll or curl upward towards the midrib centre, turn yellow, and the whole plant finally dies; the collar region shows water-soaked lesions initially and turns dark brown eventually; copious quantity of bacterial exudate is observed on the cut end of the pseudostem. The bacterium was identified as Ralstonia solanacearum based on a panel of phenotypic characters such as fluidal white colony on Kelman’s medium, biovar assay and biolog assay (BiologGN), and genotypic characters such as Multiplex-PCR based phylotyping, sequences of 16S rDNA, 16-23S intergenic region, and recN gene. Collectively these tests revealed that the R. solanacearum infecting cardamom belong to biovar 3 and phylotype 1 confirming its Asian origin. Upon soil inoculation, the bacterium caused typical wilting of the cardamom plants in three weeks and ginger plantlets in two weeks. Cross transmissibility of the bacterium was observed in cardamom and ginger wherein the plants succumbed to wilt when R. solanacearum from either of the host was inoculated. BOX-PCR fingerprinting revealed that the strain is identical (100%) to a ginger strain of R. solanacearum, which is widely prevalent in the Indian subcontinent. Furthermore, Multilocus Sequence Typing (MLST) based strain comparison confirmed that cardamom and ginger strain were identical to each other at 11 loci. Apart from striking phenotypic and genotypic (allelic) similarities, geographical origin, and cross transmissibility of the cardamom strain of R. solanacearum strongly suggest that the new occurrence of wilt of cardamom in India could have an origin in bacterial wilt of ginger. Perusal of records on Ralstoniainduced bacterial wilt in crop plants, particularly among the Zingiberaceae family, reveals that this is a new report of bacterial wilt disease in small cardamom.