First report of bacterial leaf blight on tea: an emerging threat to the Indian tea industry

Tea (Camellia sinensis (L.) O. Kuntze.) is an economically important crop extensively grown for harvestable shoots in India. In the present study, 40 tea leaf samples (new leaves/buds) showing brown to black water-soaked expanding lesions collected from different commercial tea gardens of North Bengal and Assam, India, in different seasons were analyzed for the associated factor involved in the disease. A total of 40 isolates of bacteria with similar colony appearance on agar plates were isolated from symptomatic leaves/buds. Among the 40 isolates, six representative isolates from different tea gardens including three each from North Bengal (BBN01, BBP01, and BBJ01) and Assam (BBH01, BBD01, and BBA01) were characterized for gram reactions, biochemical tests, and by sequencing the 16S rRNA gene. All the isolates were gram negative, oxidase and catalase positive, and aerobically produced acid from glucose. BLASTn analysis of the obtained sequences revealed that all six isolates were Acidovorax avenae subsp. avenae, sharing a similarity greater than 99% with A. avenae subsp. avenae sequences from the GenBank database. Phylogenetic study also displayed the closest resemblance of these isolates to A. avenae subsp. avenae based on maximum likelihood. Further, six A. avenae subsp. avenae isolates were pathogenic on a tea cultivar TV23 in repeated experiments. Koch's postulates were verified by re-isolating the bacterial pathogen from the inoculated plants showing blight symptoms. In conclusion, this study confirms that A. avenae subsp. avenae is the bacterial pathogen responsible for causing symptoms of blight in tea leaves/buds. As far as we know, this is the first record of A. avenae subsp. avenae on Indian tea plants.