Diagnostics of Fusarium wilt in banana: Current status and challenges

Global banana production is under threat from the rapidly spreading pathogen Fusarium oxysporum f. sp. cubense (Foc) tropical race 4 (TR4), which is pathogenic to Cavendish and many other varieties. Due to the absence of effective control methods and the lack of other market-acceptable resistant cultivars, early diagnostics, containment and quarantine measures are important to limit further spread and impact of this pathogen. Early detection and identification of the pathogen require reliable diagnostic assays. The reliability of a molecular diagnostic assay is directly linked to the rigour applied at validating the assay according to predetermined standards. For specific detection of a target pathogen using molecular diagnostics, a well-resolved taxonomy of the target and related species based on their evolutionary relationships is also required. The advent of sequence-based phylogenetic analysis has given rise to new insights regarding the taxonomic classification of Foc and provided proof for the polyphyletic origin of Foc races, complicating early and reliable detection of the pathogen. Although numerous diagnostic methods for Foc have been developed, choosing a rigorously validated and fit-for-purpose method for adoption is currently challenging as advantages and drawbacks for each assay are not always obvious or put into context with prior methodologies. This review compiles and critically dissects published methods that are reported to detect Foc to date and highlights their benefits and constraints to provide a valuable reference for diagnosticians, researchers and policy makers worldwide.