Integrated Management of Bacterial Wilt and Root-Knot Nematode Diseases in Pepper: Discovery of Phenazine-1-Carboxamide from Pseudomonas aeruginosa W-126

<i>Ralstonia solanacearum</i> is an important pathogen causing bacterial wilt in pepper (<i>Capsicum annuum</i> L.). The concurrent infection of <i>R. solanacearum</i> and root-knot nematodes <i>(Meloidogyne</i> spp.) exacerbates the severity of bacterial wilt in pepper. Utilizing plant endophytic bacteria to control these mixed diseases is a viable strategy. <i>Waltheria indica</i> L. (Sterculiaceae) is a traditional medicine plant. A total of 209 endophytic bacteria were isolated from <i>W. indica</i>, and <i>Pseudomonas aeruginosa</i> W-126 showed an efficient antagonistic effect against <i>R. solanacearum</i>. Based on active compound tracking principles, a compound was isolated through silica gel column chromatography and preparative HPLC combined with TLC analysis. It was identified as phenazine-1-carboxamide (PCN) by spectral techniques (ESI-MS, ¹H-NMR, ¹³C-NMR). PCN displayed excellent inhibitory activity against <i>R. solanacearum</i>, with an EC₅₀ of 64.16 μg/mL in vitro. In addition, it showed certain nematocide activity, with an LC₅₀ value of 118.63 μg/mL at 72 h. PCN also showed certain inhibitory activity against five other phytopathogenic bacteria. The structure-activity relationship indicated that the phenazine skeleton and acylamide groups were the key pharmacophores for the activity of phenazine-related compounds against <i>R. solanacearum</i>. PCN controlled the complex diseases of <i>R. solanacearum</i> and <i>M. incognita</i> in a pot experiment, with respective 51.41 and 39.80% inhibitory rates. The exploration of secondary metabolites of biocontrol bacteria can provide reference for the development of novel and efficient pesticides.