Genetic and pathogenic differentiation of Fusarium oxysporum isolates from ginger

Ginger (Zingiber officinale Roscoe) is a high-value horticultural crop widely cultivated for its culinary and medicinal applications, yet its production is increasingly constrained by soil-borne diseases. Among these, Fusarium yellows, caused by Fusarium oxysporum f. sp. zingiberi (Foz), is one of the most damaging constraints in ginger-growing regions around the world, leading to progressive yellowing, vascular blockage, and decline in rhizome quality. Members of the Fusarium oxysporum species complex are known to include both pathogenic and non-pathogenic lineages that often co-occur within the same host and environment, complicating disease diagnosis and epidemiological understanding. In this study, we examined Fusarium-like isolates recovered from both symptomatic and symptomless ginger plants within South East Queensland, the major ginger production region in Australia. We then investigated the genetic diversity, effector gene content, and pathogenic potential of these isolates. Comparative analyses revealed two genetically and functionally distinct groups: a clonal Foz lineage consistently associated with Fusarium yellows symptoms and characterised by a conserved set of Secreted In Xylem (SIX) effector genes (SIX7, SIX9, SIX10, and SIX12); and a diverse set of F. oxysporum isolates lacking these effectors. The conserved presence and co-localisation of SIX7, SIX10, and SIX12 within a 5 kb region on a 1.4 Mb contig in the Foz lineage is consistent with the retention of a stable lineage-specific effector module, likely associated with accessory genomic regions that may contribute to host specificity and pathogenicity in the Fusarium oxysporum species complex. Pathogenicity assays confirmed that only the Foz lineage induced disease, whereas non-Foz isolates caused no visible symptoms despite limited colonisation of host tissues. These findings highlight the coexistence of pathogenic and endophytic Fusarium lineages within ginger production systems and support the use of effector-based markers for improved detection and disease management.