PHENOTYPIC AND MOLECULAR CHARACTERISATION OF XANTHOMONAS AXONOPODIS PV. PUNICAE FROM POMEGRANATE LEAVES

Abstract

The present study has sought to provide insight into the blight-inciting phytopathogen Xanthomonas axonopodis pv. punicae, causing a devasting outbreak in pomegranate cultivation. Yellow-coloured circular with glistening featured colonies of five isolates of X. axonopodis pv. punicae have been phenotypically characterized and the identity of the isolates was confirmed by specific gyrB and 16S rRNA gene sequences. Results of BLAST analysis of PBL1 and PBL2 showed 99.64% and 99.76% identity with X. axonopodis pv. punicae strain 1(GenBank: KY354098.1) and strain 15 IARI (GenBank: JN036628.1) respectively. Further phylogenetic analysis revealed the strong association of X. axonopodis pv. punicae isolates with other Xanthomonas pathovars such as X. phaseoli pv. manihotis, X. citri pv. punicae and X. citri pv. mangiferaeindicae. An attempt was made to find the optimal growth media for bacterial proliferation and it was evident that NGA served as an excellent medium to support the multiplication of each isolate with a significant number of colonies (P < 0.05). The medium order per the best CFU/ml was NGA > YDCA > YGCA > NSA. The drug susceptibility test gained a lot of attention since most plant pathogens acquired resistance to antibiotics. Both streptomycin and amoxicillin could act as potentially effective drugs in inhibiting the growth of X. axonopodis pv. punicae (P 0.05). The H2O2 accumulation during the pathogen attack in the infected leaves was located by an endogenous peroxidase-dependent in situ histochemical staining method. Brown precipitate visible at a different colour intensity demonstrated the efficiency of PAMPs to trigger plant immunity to produce H2O2. The present study was the first report on the isolation and characterization of X. axonopodis pv. punicae isolated from blight-infected Pomegranate leaves from the mentioned regions of Tamil Nadu, India.