Molecular, Morphological identification, and Virulence profiling of Fusarium oxysporum f. sp. lycopersici (Sacc.) (W.C. Snyder & H.N. Hansen) associated with Root-Knot Nematode inciting Fusarium wilt of tomato

Tomato Fusarium wilt, caused by Fusarium oxysporum f. sp. lycopersici (FOL), is a major limiting factor in tomato production in Tamil Nadu. The survey was conducted in five major tomato growing districts of Tamilnadu, India (Krishnagiri, Dharmapuri, Salem, Dindigul, and Theni) in the year 2023–2024, revealed variable FOL disease incidence and pathogen distribution whereas some location showed co-infection of FOL associated with Root-Knot Nematode (RKN) (Meloidogyne incognita). Among the locations the highest disease incidence was observed in Krishnagiri district of the cultivar's CO-3 and PKM-1 were highly susceptible. All FOL isolates were collected and subjected to pathogenicity testing in pot culture and disease incidence was evaluated at 4 intervals (30, 60, 90, and 120 DAT). Based on the mean disease incidence, Fusarium isolates were divided into low, moderate and highly virulent categories. The results showed FOL-04 as the most virulent isolate. Morphological characteristics of all isolates showed significant variability in colony morphology (white, pink, purple, brown and violet), presence and absence of Microconidia, Macroconidia and Chlamydospores. Several Fusarium isolates were identified and their identity was confirmed by ITS sequencing as F. oxysporum, F. solani, F. brachygibbosum and F. equiseti. The virulent isolate FOL -04 was identified as Fusarium oxysporum f. sp. lycopersici (FOL) using TEF1-α and β-tubulin markers determining the host range of formae speciales.