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

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.

Host specificity and genetic diversity of race 4 strains of Ralstonia solanacearum

“…The most important susceptible species are turmeric, small cardamom and large cardamom – the leading spice crops in India – revealing the risk that this biovar could spread to additional commercially important Zingiberaceae species in the field in the future. Recently, bacterial wilt in small cardamom was reported in the Indian state of Kerala and was attributed to race 4/biovar 3 of R. solanacearum (Kumar et al ., ). Diverse types of symptoms such as typical curling of leaves, yellowing of leaf lamina, flagging, and rotting of the leaf lamina, rhizomes and pseudostem near the collar region were observed.…”

“…The annual occurrence of bacterial wilt of ginger in the months of the southwest monsoon is predictable in southern and northeastern Indian states, these regions being leading producers of several spices in the world and which are considered as endemic areas for bacterial wilt. These spice plants in the family Zingiberaceae can be considered as collateral hosts of biovar 3 strains (Kumar et al ., ). Close proximity of ginger fields and small cardamom plantations was blamed for the recently reported outbreak of bacterial wilt in small cardamom plants in India (Kumar et al ., ).…”

“…), kahili ginger ( Hedychium gardnerianum ) and shampoo ginger ( Zingiber zerumbet ; Kumar & Hayward, ; Paret et al ., ). The isolates causing bacterial wilt of small cardamom and edible ginger ( Zingiber officinale ) are genetically and phenotypically identical according to MLST‐based genotyping and cross‐inoculation assays (Kumar et al ., ).…”

“…Ralstonia solanacearum has been reported to infect small cardamom ( Elettaria cardamomum ; Kumar et al ., ), alpinia ( Alpinia spp. ; Hayward, ), turmeric ( Curcuma longa ; Velupillai, ), sand ginger ( Kaempferia galanga ; He, ), siam tulip ( Curcuma alismatifolia ) and mioga ( Zingiber mioga ; Tsuchiya et al ., ), red ginger ( Alpinia purpurata ), white ginger ( Hedychium coronarium ), red ginger lily ( Etlingera elatior ), white turmeric ( Curcuma zeodaria ), yellow ginger ( Hedychium flavescens ), beehive ginger ( Zingiber spectablis ), globba ( Globba sp.…”

Draft Genome Sequence of Highly Virulent Race 4/Biovar 3 of Ralstonia solanacearum CaRs_Mep Causing Bacterial Wilt in Zingiberaceae Plants in India

“…In India, race 4/biovar 3 is primarily responsible for wilt in plants belonging to the Zingiberaceae family (3–6). Ralstonia solanacearum CaRs_Mep, a race 4/biovar 3 pathogen, was isolated from bacterial wilt affecting small cardamom plants originating from Meppadi (11.5550°N, 76.1349°E), Wyanad district of the southern Indian state of Kerala (7). Although the genome sequence of race 4/biovar 4 is already published (8), the genome sequence of race 4/biovar 3, the highly virulent lineage of race 4, is not reported yet.…”