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Fusarium wilt of banana, caused by the pathogen Fusarium oxysporum f. sp. cubense tropical race 4 (Foc TR4), is a threat to food security as it affects the global banana industry. Control of this pathogen is complex due to the lack of resistant banana or plantain genotypes, lack of effective commercial fungicides, the production of chlamydospores, late appearance of symptoms in infected plants, high adaptability of the pathogen to diverse soil conditions and the polycyclic nature of the disease. Currently, the management strategy for Foc TR4 is exclusion and eradication, which is costly for the producer and the environment because the plants are treated with glyphosate and the affected area is quarantined for a long time. Thus, the development of early detection strategies for Foc TR4 from environmental samples and asymptomatic tissues with low inoculum concentration is essential; this would enable restriction of pathogen spread and minimize the environmental impact by eradication only in areas with accurate data of the pathogen's presence. In this study, three different PCR technologies (conventional PCR, quantitative PCR and droplet digital [dd] PCR) were evaluated for Foc TR4 detection in complex environmental samples. We report the development of a sensitive and specific ddPCR primer/probe set and protocols that can be used as a tool for Foc TR4 detection from symptomatic and asymptomatic plant tissue without prior DNA extraction. The limits of detection in drainage waters, footbaths and soil samples were evaluated using artificial inoculation assays. Finally, environmental samples from Foc TR4‐affected fields were analysed. [ABSTRACT FROM AUTHOR]

The vascular wilt disease caused by the fungus Fusarium oxysporum f. sp. physali (Foph) is one of the most limiting factors for the production and export of cape gooseberry (Physalis peruviana) in Colombia. A transcriptomic analysis of a highly virulent strain of F. oxysporum in cape gooseberry plants, revealed the presence of secreted in the xylem (SIX) effector genes, known to be involved in the pathogenicity of other formae speciales (ff. spp.) of F. oxysporum. This pathogenic strain was classified as a new f. sp. named Foph , due to its specificity for cape gooseberry hosts. Here, we sequenced and assembled the genome of five strains of F. oxysporum from a fungal collection associated to the cape gooseberry crop (including Foph), focusing on the validation of the presence of SIX homologous and on the identification of putative effectors unique to Foph. By comparative and phylogenomic analyses based on single-copy orthologous, we found that Foph is closely related to F. oxysporum ff. spp., associated with solanaceous hosts. We confirmed the presence of highly identical homologous genomic regions between Foph and Fol that contain effector genes and identified six new putative effector genes, specific to Foph pathogenic strains. We also conducted a molecular characterization using this set of putative novel effectors in a panel of 36 additional stains of F. oxysporum including two of the four sequenced strains, from the fungal collection mentioned above. These results suggest the polyphyletic origin of Foph and the putative independent acquisition of new candidate effectors in different clades of related strains. The novel effector candidates identified in this genomic analysis, represent new sources involved in the interaction between Foph and cape gooseberry, that could be implemented to develop appropriate management strategies of the wilt disease caused by Foph in the cape gooseberry crop. [ABSTRACT FROM AUTHOR]

Summary: RNA sequencing (RNAseq) reads from cape gooseberry plants (Physalis peruviana) infected with Fusarium oxysporumf. sp. physali (Foph) were mapped against the lineage‐specific transcriptome of Fusarium oxysporumf. sp. lycopersici (Fol) to look for putative effector genes. Homologues of Fol SIX1(designated SIX1a and SIX1b), SIX7, SIX10, SIX12, SIX15 and Ave1were identified. The near identity of the Foph and Fol SIX7, SIX10 and SIX12genes and their intergenic regions suggest that this gene cluster may have undergone recent lateral transfer. Foph SIX1a and SIX1bwere tested for their ability to complement a SIX1 knockout mutant of Fol. This mutant shows reduced pathogenicity on susceptible tomato plants, but is able to infect otherwise resistant tomato plants carrying the I‐3 gene for Fusarium wilt resistance (SIX1 corresponds to Avr3). Neither SIX1a nor SIX1b could restore full pathogenicity on susceptible tomato plants, suggesting that any role they may play in pathogenicity is likely to be specific to cape gooseberry. SIX1b, but not SIX1a, was able to restore avirulence on tomato plants carrying I‐3.These findings separate the recognition of SIX1 from its role as an effector and suggest direct recognition by I‐3. A hypervariable region of SIX1undergoing diversifying selection within the F. oxysporum species complex is likely to play an important role in SIX1 recognition. These findings also indicate that I‐3could potentially be deployed as a transgene in cape gooseberry to protect this emerging crop from Foph.Alternatively, cape gooseberry germplasm could be explored for I‐3homologues capable of providing resistance to Foph. [ABSTRACT FROM AUTHOR]

In Colombia, tomato production under protected conditions represents an important economic contribution to the agricultural sector. Fusarium wilt diseases, caused by pathogenic formae speciales of the soil-borne fungus Fusarium oxysporum Schltdl., cause significant yield losses in tomatoes throughout the world. Investigation of the F. oxysporum–tomato pathosystem in Colombia is required to develop appropriate alternative disease management. In this study, 120 fungal isolates were obtained from four different departments in the Central Andean Region in Colombia from tomato crops with symptoms of wilt disease. A molecular characterization of the fungal isolates was performed using the SIX1, SIX3, and SIX4 effector genes of Fusarium oxysporum f. sp. lycopersici W.C. Snyder & H.N. Hansen (Fol). Additionally, we developed a new specific marker to distinguish between Fusarium oxysporum f. sp. radicis-lycopersici Jarvis & Shoemaker (Forl) and Fol isolates. Furthermore, a phylogenetic analysis using the Translation Elongation Factor 1-alpha (EF1a) gene was performed with the collected isolates. Two isolates (named Fol59 and Fol-UDC10) were identified as Fol race 2, four isolates were identified as Forl, six isolates were identified as F. solani, and most of the isolates were grouped within the F. oxysporum species complex. The phylogenetic tree of EF1a showed that most of the isolates could potentially correspond to nonpathogenic strains of F. oxysporum. Additional pathogenicity assays carried out with Fol59 and Fol-UDC10 confirmed that both isolates were highly virulent strains. This study represents a contribution to the understanding of the local interaction between tomatoes and F. oxysporum in Colombia. [ABSTRACT FROM AUTHOR]