Comparative gene expression studies of candidate genes associated with defence response in ginger and mango ginger post inoculation with Ralstonia solanacearum

Bacterial wilt of ginger (Zingiber officinale Rosc.) causes serious economic losses in all major ginger growing areas of the world. The Indian mango ginger (Curcuma amada Roxb.) is found to be resistant to the disease. With an aim to decipher the factors involved in mango ginger resistance, tissue-specific expression of nine candidate genes viz., Ethylene Response Factor (ERF), HMG-CoA synthase (HMGS), HMG-CoA reductase (HMGR), ABC transporter, WRKY8 transcription factor, β-(1, 3)-glucanase, Callose synthase, Heat Shock Protein (HSP) and Mlo14 were carried out at different time intervals in leaf and rhizome tissues post pathogen inoculation using real-time PCR. The transcripts varied in the level of up and down-regulation, with a marked difference in the intensity and time of response. Compared to leaf tissues, the rhizome tissues of both the plants showed increased expression of all the transcripts except β-(1, 3)-glucanase and Mlo14. In both the resistant and susceptible plants β-(1, 3)-glucanase showed higher expression in the leaf tissues, whereas HSP and Callose synthase showed higher expression in rhizome tissues of ginger and mango ginger respectively. Compared to ginger, the rhizome tissues of mango ginger showed peak level expression at earlier hours. The rhizome of mango ginger may play an important role in preventing the entry of the pathogen through the soil. Traversing all these barriers if the pathogen is delivered directly to the xylem tissues, they can multiply profusely and induce bacterial wilt in mango ginger.