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.

The root-knot nematode Meloidogyne spp. causes yield losses of up to 68% on tomato (Solanum lycopersicum L.) crops. Genetic resistance in the host plant makes the crop sustainable and it can breakdown when there is a high population density of the pathogen. The objective of this study was to determine the nematode population density that allow determining the resistance potential of tomato germplasm associated with the Mi-1 resistance gen. The Mi-1 gene was evaluated with the molecular marker SCAR Mi-23 and specific primers in the genotypes COLY007, IAC1687, LA0445, IAC1622 and two commercial controls (susceptible and resistant). The damage scale and the number of individuals recovered (eggs and juveniles) were assessed, with different population densities of the pathogen inoculated (0, 1000, 2000, 3000, 4000 and 5000 individuals plant^-1), in a split plot design, with six replicates and a plant as the experimental unit. The genotype IAC1687 and the resistant commercial control presented the resistance allele of the Mi-1 gene and were classified as moderately resistant to a density of 1000 individuals plant^-1. Despite having the Mi-1 gene, the COLY007 genotype was classified as moderately susceptible and with densities greater than 1000 individuals plant^-1 can break resistance in all genotypes evaluated. Additionally, it is necessary to correlate the genotypic and phenotypic responses to guarantee the success of the selection supported by molecular markers such as SCAR Mi-23 and identify promising genotypes that could be included in a long-term breeding and also used as rootstocks in an integrated management of root-knot nematode.

In this study, 55 tomato genotypes from different geographical regions were evaluated with ISSR markers (Inter Simple Sequence Repeats). The seven ISSR primers originated 63 amplified bands, of which 90.48% were polymorphic. The cluster analysis based on the Nei-Li similarity coefficient using the average genetic clustering method (UPGMA) revealed the conformation of five clusters at a level of similarity of 72%. The ISSR technique did not discriminate tomato genotypes according to the species or region of provenance. The STRUCTURE analysis and the dendrogram did not reveal a genetic structure in the population evaluated. The genotypes of the species of S. pimpinellifolium, S. l. cerasiforme, S. lycopersicum and S. peruvianum were found consistently grouped, showing a close genetic relationship among them. A high genetic variation among the individuals within each of the groups formed was suggested by the AMOVA. The ISSR markers were effective in assessing the genetic diversity and structure of populations of tomato genotypes. The high genetic variability found in this study indicates the valuable genetic potential present in tomato germplasm, especially of wild species, which could be used for future breeding programs of the species.

Much of the diversity of tomato is found in wild forms, the most important being the Solanum lycopersicum L. var. cerasiforme and S. pimpinellifolium. The objective of this research was to assess the genetic diversity of 30 introductions of cherry tomato with 36 microsatellite molecular markers. The study was conducted at the Plant Transformation Research Center (PTRC) of the University of California. A dendrogram was built using the Dice-Nei and Li similarity index and the UPGMA clustering method, where introductions were differentiated without preserving a distribution pattern obeying the geographical area of origin. A coefficient of genetic differentiation was found (Fst = 0.3474), showing a high genetic differentiation of the introductions; those from Brazil, Ecuador, and Peru were the most genetically diverse, presenting 100% of polymorphic loci. The molecular variance analysis indicated a variation of 11% between the groups and 89% within the same. The broad genotypic variability of the evaluated introductions favors the possibility of selecting those for genetic improvement and sustainable use of the species.

The interaction between plants and pathogens is a very dynamic and complex relationship that also includes a high degree of specificity, and it is precisely this last characteristic which triggers such important responses in the survival of one or the other. The pathosystem formed by tomato (Solanum lycopersicum L.) and Fusarium oxysporum f. sp. lycopersici (Fol) has been the subject of multiple studies due to the importance of the vegetable worldwide and for the economic and ecological impact of the fungus responsible for the vascular wilt disease in tomato, causing losses that go up to 100%. One way to find alternatives for the management of any pathosystem is to know the actors involved and the mechanisms that govern the interaction through technological and scientific advances that clearly show how the interaction develops on a genetic level. This review collects the information from different scientific sources with focus on the knowledge of the fungus, tomato cultivation and plant defense applied to this pathosystem, as well as the molecular mechanisms.

Background: Fusarium oxysporum f. sp. lycopersici (Fol) is a compendium of pathogenic and non-pathogenic fungal strains. Pathogenic strains may cause vascular wilt disease and produce considerable losses in commercial tomato plots. To gain insight into the molecular mechanisms mediating resistance to Fol in tomato, the aim of our study was to characterize the transcriptional response of three cultivars (CT1, CT2 and IAC391) to a pathogenic (Fol-pt) and a non-pathogenic (Fo-npt) strain of Fo. Results: All cultivars exhibited differentially expressed genes in response to each strain of the fungus at 36 h post-inoculation. For the pathogenic strain, CT1 deployed an apparent active defense response that included upregulation of WRKY transcription factors, an extracellular chitinase, and terpenoid-related genes, among others. In IAC391, differentially expressed genes included upregulated but mostly downregulated genes. Upregulated genes mapped to ethylene regulation, pathogenesis regulation and transcription regulation, while downregulated genes potentially impacted defense responses, lipid transport and metal ion binding. Finally, CT2 exhibited mostly downregulated genes upon Fol-pt infection. This included genes involved in transcription regulation, defense responses, and metal ion binding. Conclusions: Results suggest that CT1 mounts a defense response against Fol-pt. IAC391 exhibits an intermediate phenotype whereby some defense response genes are activated, and others are suppressed. Finally, the transcriptional profile in the CT2 hints towards lower levels of resistance. Fo-npt also induced transcriptional changes in all cultivars, but to a lesser extent. Results of this study will support genetic breeding programs currently underway in the zone.