Molecular Characterization, Virulence Diversity, and Host Genome-Dependent Resistance to Ralstonia syzygii subsp. celebesensis Causing Banana Blood Disease in Southern Thailand

Banana blood disease caused by Ralstonia syzygii subsp. celebesensis threatens banana production across Southeast Asia, with recent reports indicating disease establishment in southern Thailand. Comprehensive surveys were conducted across eight districts of Yala Province during 2021-2022 to assess disease distribution and characterize the pathogen population. Disease symptoms were observed in five districts (Betong, Bannang Sata, Than To, Yaha, and Krong Pinang), with 41 bacterial isolates obtained from symptomatic Saba banana plants. Recent observations indicate disease has since spread to all districts of Yala Province, demonstrating rapid geographic expansion. All isolates displayed characteristic slow-growing, creamy white colonies with dark-red centers on TZC medium. Species-specific PCR using 759F/760R primers confirmed all isolates as members of the Ralstonia solanacearum species complex. Phylotype-specific multiplex PCR consistently identified all strains as phylotype IV, while BDB-specific duplex PCR definitively confirmed identity as R. syzygii subsp. celebesensis. DNA sequencing of five representative isolates showed 99.28% similarity with reference sequences from Indonesia and Malaysia (GenBank accessions CP019911.1 and FR854071.1). Pathogenicity testing revealed that 85.4% of isolates were highly virulent, causing 75-100% plant mortality within 10-14 days post-inoculation. Disease resistance screening of 11 banana cultivars demonstrated strong genomic effects, with AA genome cultivars (wilt index 1.2-1.5) showing significantly greater resistance compared to ABB and BBB genome cultivars (wilt index 2.4-2.9). The uniform genetic profile across all isolates, combined with concentrated disease occurrence in border areas adjacent to Malaysia, suggests recent single-source pathogen introduction through cross-border transmission. The rapid geographic expansion demonstrates urgent need for comprehensive quarantine measures and coordinated management strategies to prevent further disease spread in Thailand and neighboring countries.