Loop-Mediated Isothermal Amplification Assay for the Detection of Citrus Canker Causing Bacterial Variant,...

Citrus canker, a highly transmissible bacterial disease, has three major types, with Asiatic canker (Canker A), caused by Xanthomonas citri pv. citri (Xcc A), being the most widespread and severe, affecting most citrus varieties. Xcc A has two mild variants, Xcc A* and A^w with a limited host range, reported in Southwest Asia and Florida, respectively. Since 2015, the canker caused by Xcc A^w has been being reported in the Rio Grande Valley of South Texas where the Texas commercial citrus industry is located. In 2016, a more severe Canker A was reported in the upper Texas gulf coast region, north of the Rio Grande Valley, posing a potential threat to the Texas citrus industry. Given that existing diagnostic methods cannot reliably distinguish Xcc A^w from Xcc A, we developed a loop-mediated isothermal amplification (LAMP) assay specific to Xcc A^w (LAMP-A^w) for rapid, field-based identification of this bacterial variant. The detection limit of LAMP-A^w was ~4.52 Log₁₀ copies of the target molecule. This study also evaluated the field applicability of the LAMP-A^w assay by coupling the LAMP-A^w assay with a lateral flow immunoassay system.