Abstract

Background: Fusarium wilt disease, which is caused by Fusarium oxysporum f. sp. lycopersici (Fol) is a destructive soil borne illness that greatly affects tomato production globally. It is important to determine genetic variability and pathogenicity of F. oxysporum isolates to become able to develop effective measures to manage the disease. Objective: The purpose of the study was to describe major tomato producing regions in Iraq in F. oxysporum isolates and determine their pathogenicity in greenhouse and field environments. Methods: In the 2024-2025 tomato growing seasons, forty-five F. oxysporum isolates were obtained in five Iraqi provinces (Baghdad, Babylon, Najaf, Diyala, and Wasit) on symptomatic tomatoes. Species identification and phylogenetic analysis of the species molecular diagnostics was done by use of species-specific primers targeting translation factor 1 alpha (TEF-16) and intergenic spacer (IGS) regions. Pathogenicity was experimented in the greenhouse and field experimental on the weak tomato cultivar of Moneymaker. Morphological characterization and fungus biomass determination through real-time PCR were done. Results: Three physiological races of Fol were determined: race 1, 31.1% (race 2, 48.9% and race 3, 20.0%), race 2 having the majority. Test of pathogenicity showed that there was a broad spectrum of disease severity indices ranging between 22.4 percent and 89.7 percent in the greenhouse and 18.6 percent to 82.3 percent in the field. The most violent isolates (Fol-B12, Fol-N18 and Fol-D23) belonged to race 2 and led to the total wilting of the plants in 21 days. Morphological differences were seen in morphology of the colony, sporulation and morphological growth rates of the colonies. Quantification of fungal biomass in real-time PCR indicated that the highly virulent isolates had a large amount of fungal biomass compared to moderately virulent isolates. Conclusions: The paper brings out the genetic diversity and pathogenicity of F. oxysporum isolates in tomato farms in Iraq. Such results are crucial in the development of disease management strategies, as well as development of resistant tomato species.