Isolation, Identification, and Pathogenicity of Bacterial Wilt Pathogens Associated with Ginger in Kano, Nigeria

Abstract

Bacterial wilt remains a major constraint for ginger (Zingiber officinale L.) in most ginger-growing regions of Nigeria, with post-harvest losses exceeding 90%. Ralstonia solanacearum is widely recognized as the primary causal agent of the disease. This study set out to isolate, molecularly identify, and confirm the pathogenicity of bacterial pathogens associated with ginger wilt in Kano State, Nigeria. Biochemical tests and carbohydrate oxidation patterns grouped the isolates into typical R. solanacearum biovars (I and V). However, 16S rRNA sequencing and maximum-likelihood phylogenetic analysis revealed non-Ralstonia pathogens. The causal agents were identified as Alcaligenes sp. (CG09, YG018, and YG019; 97.40% similarity for CG09) and a Brucellaceae-related taxon (CG011; 91.73% similarity). Pathogenicity tests confirmed these strains as virulent, with 100% wilt incidence (p=0.42) in inoculated plants at 21 days post-inoculation and Koch's postulates fulfilled after successful re-isolation. Sequences for CG09 and CG011 have been deposited in GenBank under accession numbers PZ682642 and PZ682641, respectively. This study provides preliminary evidence of Alcaligenes sp. and a Brucellaceae-related taxon as causal agents of bacterial wilt of ginger in Nigeria. It points out the necessity of using molecular tools to confirm traditional biochemical assays for accurate pathogen identification and effective disease management in Nigerian ginger production.