Strain-specific virulence and stress adaptation in Ralstonia pseudosolanacearum: Implications for bacterial wilt diagnostics and control

Abstract

Ralstonia pseudosolanacearum, a major phytopathogen within the R. solanacearum species complex, causes bacterial wilt in a wide range of crops and exhibits strain-specific differences in virulence and environmental resilience, posing significant challenges for disease management. This study compared two closely related strains, QK and YNQK, both classified as phylotype I, biovar III, but differing markedly in pathogenicity and stress tolerance. Pathogenicity assay revealed that YNQK exhibits significantly higher pathogenicity in Nicotiana benthamiana, causing severe wilting, whereas QK-infected plants remained largely asymptomatic. Strain YNQK exhibited higher resistance to stresses of acid (pH 5.0), alkali (pH 9.5), drought (PEG6000 > 20 %), 45 mM H₂O₂, and 1000 mg/L Cd²⁺, while strain QK showed lower tolerance under similar conditions. Under drought stress, strain YNQK produced more exopolysaccharides (89.70 μg/mL) than QK (65.67 μg/mL), and under H₂O₂ stress, it exhibited higher biofilm production and antioxidant enzyme activity. Comparative genomics revealed that strain YNQK uniquely holds key genes, including PopF2 (pathogenic), chrC (chromate resistance), and cnrA, B, C, H, Y (cobalt and nickel resistances). Both strains shared core osmotic stress-related genes involved in K⁺ transport (kup), proline and betaine biosynthesis (proA/B/C, betA/B, gbsA), and biofilm formation (eps, pga, rfb clusters). These findings highlight the role of genetic variation in shaping strain-specific virulence and abiotic stress tolerance in R. pseudosolanacearum. While the pathogenicity assays in this study relied on leaf infiltration rather than natural root infection, which may bypass early host defenses, the results nonetheless provide valuable insight into strain-level differences and inform the development of more precise diagnostic and management strategies.