Outbreak of tomato wilt caused by Ralstonia solanacearum in Tamil Nadu, India and elucidation of its genetic relationship using multilocus sequence typing (MLST)

摘要

High incidence of wilt disease (35-45%) of tomato (Solanum lycopersicum L.) was recently observed in two different locations of Tamil Nadu state of India. Infected plants showed typical wilt symptoms which include sudden green wilting of foliage followed by drooping of leaves downwards. The characteristic white milky ooze observed on the cut end of infected stem indicated bacterial etiology. Upon isolation, bacterium produced white fluidal irregular colonies with characteristic pink center on 2, 3, 5 triphenyl tetrazolium chloride amended nutrient medium. The bacterium caused typical green wilting 4-5 days post inoculation (dpi) on one month old tomato plants. The identity of bacterium was confirmed as Ralstonia solanacearum using 16S rRNA gene sequences as well as by R. solanacearum specific PCR. Further studies confirmed that the bacterium belonged to race 1 and biovar 3. In depth genetic characterization using multilocus sequence typing (MLST) revealed that the wilt outbreaks in Tamil Nadu were caused by genetically distinct race 1 strains of R. solanacearum. While the isolate, TRsR found clustered with R. solanacearum isolates previously reported from Andaman and Nicobar Islands-India, TRsP is clustered with isolates reported from Kerala, India. The results of our MLST based genetic analysis clearly indicated horizontal spread of bacterial wilt disease of tomato as a consequence of pathogen migration with the expansion of cultivation in India.