Emerging Role of Fusarium equiseti in Tomato Fusarium Wilt in Vietnam

Background and Objective: Tomato Fusarium wilt caused by Fusariumspecies is a major constraint to tomato production worldwide, including in Vietnam. However, comprehensive identification of the causal agents associated with the disease in major tomato-growing regions of the country remains limited. This study aimed to identify Fusarium species associated with tomato Fusarium wilt and evaluate their pathogenicity. Materials and Methods: Tomato plants showing wilt and root rot symptoms were collected from commercial farms near Da Lat City, Lam Dong Province, Vietnam (March 2023). Associated pathogens were isolated from surface-sterilized root and stem tissues on PDA and purified using monosporic culture techniques. Isolates were characterized based on cultural and microscopic features on PDA and CLA, and further identified through ITS rDNA sequencing and phylogenetic analysis. Pathogenicity was evaluated using blotter and pot assays on tomato seeds under controlled conditions. Data were statistically analyzed using ANOVA at p<0.05, and representative sequences were deposited in GenBank for molecular confirmation. Results: The isolates were identified as Fusarium equiseti(seven isolates) and F. oxysporum(one isolate), showing distinct morphological features. All isolates were pathogenic and caused seed rot, reduced germination, collar rot, vascular browning, and seedling mortality, although pathogenic variability was observed among isolates. Representative isolates, F. equisetiTo2521 and F. oxysporumTo7031, exhibited the highest virulence. Disease symptoms caused by both species were similar and difficult to distinguish under field conditions. Notably, F. equisetiwas isolated more frequently than F. oxysporum, indicating its dominant association with the local disease complex. Conclusion: This study provides the first evidence that F. equiseti, previously regarded mainly as a root rot pathogen, is a major causal agent of tomato Fusarium wilt in Vietnam. The emergence of this pathogen suggests a possible shift in disease epidemiology and emphasizes the importance of molecular diagnostics, continuous pathogen surveillance, and the development of revised disease management strategies.