Phylotype and sequevar analysis of a Ralstonia pseudosolanacearum causing wilt in marigold (Tagetes erecta)

Abstract

Bacterial wilt disease is caused by the Ralstonia species (R. solanacearum, R. pseudosolanacearum, and R. syzygii). It is the most serious soil-borne disease of many economically important crops including tomato, potato, chili pepper, tobacco, and eggplant. Marigold (Tagetes erecta) is an important commercial flower crop in Thailand and has been severely affected by this bacterial wilt disease. The purpose of this study was to identify six isolates of Ralstonia spp. collected from wilting marigolds. Taking into consideration symptoms, stem-streaming tests, and characteristic growth on the TZC medium, the causal agent was preliminarily identified as a Ralstonia sp. The results of a pathogenicity test revealed that all six isolates were highly virulent to marigold and tomato but only moderately virulent to chili pepper and eggplant. Determination of isolate phylotype used a Pmx-PCR assay which revealed that all the isolates detected were phylotype I, and thus Ralstonia pseudosolanacearum. The isolates were further classified as sequevar 13 based on partial egl and hrpB gene sequences. This study determined that the bacterial pathogens from marigold belonged to phylotype I as R. pseudosolanacearum and sequevar 13.