New insights into the diversity and pathogenicity of Fusarium species causing carnation wilt in Lam Dong, Vietnam.

Carnation Fusarium wilt (CFW) is a devastating systemic disease affecting carnation production worldwide, although little is known about its status in Vietnam. This study provides the first comprehensive report on the population and pathogenesis profile of Fusarium species associated with CFW in Vietnam. A survey of commercial greenhouses revealed approximately 10.7% disease incidence, with symptomatic plants showing chlorosis, wilting, leaf blight, and vascular discoloration. Twenty-one Fusarium isolates were obtained and classified into the Fusarium oxysporum species complex (FOSC) and F. incarnatum-equiseti species complex (FIESC), each comprising two morphologically distinct clades. Molecular identification based on ITS and TEF-1α sequences confirmed four species: F. oxysporum (42.9%), F. pernambucanum (33.3%), F. sulawesiense (19.0%), and F. nirenbergiae (4.8%), revealing notable species diversity. Pathogenicity tests at both seed germination and transplant stages showed that all identified species could cause disease, with varying degrees of aggressiveness. Fusarium oxysporum species complex isolates mainly delayed germination, while FIESC isolates more strongly reduced germination rates. Both complexes caused root rot, seedling death, and foliar symptoms in transplants. Two highly virulent isolates, C1611 (F. oxysporum) and C2111 (F. pernambucanum), significantly reduced seed viability and survival and caused high disease intensity. Some isolates showed organ- or stage-specific pathogenicity. This is the first report of F. pernambucanum, F. sulawesiense, and F. nirenbergiae associated with carnation, globally, and the first record of CFW-associated species in Vietnam. These findings highlight the diversity and pathogenic complexity of Fusarium species involved in CFW and underscore the need for accurate identification and effective disease management strategies in local and international trade.