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. 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. 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.

中文翻译：

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柑橘溃疡病原菌柑橘黄单胞菌亚种的生物防治。使用朗布尔石灰内生菌的柑橘

朗布尔石灰 (RL) 是世界范围内使用的常见砧木品种。然而，众所周知，它对柑橘溃疡病 (CC) 具有很高的易感性。为了满足对健康柑橘幼苗日益增长的需求，本研究旨在研究 RL 内生细菌作为 CC 病原体柑橘黄单胞菌亚种生物防治剂的效力。柑橘。从健康的 RL 叶子中收集分离物，并在体外和植物中对 XCC 及其无细胞上清液 (CFS) 进行拮抗试验。根据其 16S rDNA 序列相似性鉴定潜在分离株。从健康的 RL 树的叶子中获得了多达 21 个分离物。两种（B1 和 C8）分离物表现出对 XCC 的有希望的抑制活性。基于体外试验，这些分离株的细胞悬液（CS）能有效抑制XCC的生长，最佳净区直径分别为8.41和7.51 mm。与 CS 一致，他们的 CFS 对 XCC 也表现出类似的拮抗效力，记录的最高透明区分别为 7.23 毫米和 6.22 毫米。进一步研究表明，B1 和 C8 CFSs 的最低抑制浓度为 25 µg/ml。还发现两种 CFS 都对高温和极低的 pH 值敏感，但在蛋白酶 K 存在下稳定。在体内试验中，B1 和 C8 的 CS 和 CFS 处理都可以有效地保护 Rangpur 石灰免受 CC。与对照植物相比，处理过的植物的发病率显着降低，症状较轻。根据他们的 16S rDNA 序列，B1 和 C8 分别被鉴定为巴氏葡萄球菌和华氏葡萄球菌。得出结论，巴氏葡萄球菌和华氏葡萄球菌可能是有希望的XCC生物防治剂。这些细菌分离物可用作 CC 的替代预防措施，而不是常用的化学品。