Genetic Diversity and Pathogenicity of <i>Thielaviopsis</i> <i>paradoxa</i> Isolates and Implications for Coconut Palm Disease Management

<i>Thielaviopsis</i> <i>paradoxa</i> is an important soilborne pathogen causing bleeding disease and stem rot of coconut and other palm species, posing a serious threat to coconut production in Hainan Province, China. This study investigated the biological characteristics, pathogenic variability, and genetic diversity of <i>T</i>. <i>paradoxa</i> isolates collected from coconut palms in this region, where population-level data remain limited. Isolates exhibited variability in mycelial growth and sporulation under different temperature, pH, and nutrient conditions, indicating physiological differentiation among strains. Pathogenicity assays across multiple coconut varieties revealed four pathogenicity types, with some isolates consistently showing greater aggressiveness. Genetic analysis based on ISSR markers revealed a high level of genetic diversity (82.96% polymorphism). Genetic clustering showed partial associations with geographic origin, host source, and pathogenicity patterns; however, these relationships are correlative and do not imply causality. Overall, this study provides the first region-specific synthesis of physiological traits, pathogenic variability, and ISSR-based genetic diversity of <i>T</i>. <i>paradoxa</i> in Hainan, contributing baseline information for future population genomic studies and supporting the development of improved disease management strategies for coconut palms.