Biological control of citrus canker pathogen Xanthomonas citri subsp. citri using Rangpur lime endophytic bacteria

Abstract

Abstract Background Rangpur lime (RL) is a common rootstock cultivar used worldwide. However, it is known to have a high susceptibility to citrus canker (CC). To meet the increasing demand for healthy citrus seedlings, this research aimed to study the potency of RL endophytic bacteria as a biocontrol agent of the CC pathogen Xanthomonas citri subsp. citri. The isolates were collected from healthy RL leaves and subjected to in vitro and in planta antagonistic tests against XCC, alongside its cell-free supernatant (CFS). Potential isolates were identified according to their 16S rDNA sequence similarities. Results As many as 21 isolates were obtained from the leaves of healthy RL trees. Two (B1 and C8) isolates demonstrated promising inhibitory activity against XCC. Based on the in vitro assays, the cell suspensions (CS) of these isolates could effectively inhibit the growth of XCC, with an optimum clear zone diameter of 8.41 and 7.51 mm, respectively. Consistent with CS, their CFSs also displayed similar antagonistic potencies against XCC with the highest clear zone recorded being 7.23 mm and 6.22 mm, respectively. Further investigations revealed that the minimum inhibitory concentration of B1 and C8 CFSs was 25 µg/ml. It was also found that both CFSs were sensitive to high heat and very low pH, but stable in the presence of proteinase-K. In the in vivo assay, both CS and CFS treatments of B1 and C8 could effectively protect the Rangpur lime from CC. Treated plants had significantly lower disease incidences and developed less severe symptoms than the control plants. Based on their 16S rDNA sequence, B1 and C8 were identified as Staphylococcus pasteuri and Staphylococcus warneri, respectively. Conclusion It was concluded that Staphylococcus pasteuri and Staphylococcus warneri could be promising biocontrol agents of XCC. These bacterial isolates can be used as an alternative prevention measure to CC as opposed to commonly used chemicals.