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Priyanka Krishna ¹, M. K. Prasanna Kumar ¹, Manjunatha Channappa ², Pramesh Devanna ³, Kartar Singh ⁴, Puneeth M. Eeregowda ¹, H. B. Mahesh ¹, B. S. Chandrashekar ¹, Venkatesh Babu ⁵, Radhika U. Desai ¹, Sahana N. Banakar ¹

Affiliations
1 Department of Plant Pathology, University of Agricultural Sciences (UAS), Bengaluru 560 065, IN
2 ICAR-Indian Agricultural Research Institute, Regional Station, Wellington 643 231, IN
3 Agricultural Research Station, Gangavati, UAS, Raichur 584 104, IN
4 ICAR-National Bureau of Plant Genetic Resources, Regional Station, Jodhpur 342 005, IN
5 Centre for Advanced Studies in Botany, University of Madras, Guindy Campus, Chennai 600 005, IN

Abstract

Bacterial blight caused by Xanthomonas axonopodis pv. punicae (Xap) is one of the economically important diseases of pomegranate in India. Under field conditions, the disease is being managed using antibiotics and copper-based compounds but with limited success due to their poor bio-efficacy. The reduced efficacy of antibiotics and copper compounds against field populations of Xap might be due to the development of bactericide resistance through acquired genes. In the present study, ten bacterial blight-infected pomegranate samples were collected from different geographic locations of Karnataka, India, and causal agent Xap was isolated and identified through 16S rRNA sequencing. Streptomycin resistance genes such as rpsL, strA, strB and copper resistance genes copL, copB were detected using gene-specific primers in PCR. All ten isolates were positive for streptomycin resistance genes whereas copper resistance gene copB was absent in three isolates (Xap1, Xap4, Xap6) while copL was absent in Xap4 and Xap6 isolates. Further, in vitro experiments using different concentrations of streptomycin on culture media showed lowest growth inhibition up to 1500 μg/ml concentration, supporting the molecular evidence of antibiotic resistance. The present study provides preliminary information on the presence of antibiotic resistance genes in the field populations of Xap.

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