Natural Occurrence, Morpho-Molecular Characteristics, and Pathogenicity of Fusarium spp. Associated With Chrysanthemum Wilt in Vietnam

Chrysanthemum Fusarium wilt (CFW) is a devastating soil-borne disease affecting the cut chrysanthemum industry globally. In Vietnam, this disease has been occurring silently and is posing a risk of epidemic outbreaks in the southern provinces, especially Lam Dong. Results from a survey in 2023 showed that stunted growth, curved and small stems, dried-rot roots, leaf drooping and green or yellow wilting of plants after transplanting or at their flower bud initiation were common symptoms observed across the main chrysanthemum-growing farms in Lam Dong. The occurrence of CFW was recorded in relation with the host cultivar, irrigation method and fungicide-spraying regime. Among the cultivars grown in Lam Dong, 'Doa cu' was the most susceptible to CFW. The use of sprinkler irrigation and infrequent application of fungicides were attributed to increase both disease incidence and severity. Thirty fungal isolates obtained from diseased plants were identified as Fusarium oxysporum and F. falciforme based on morphological features and molecular analysis of ITS and TEF-1 alpha genes. The detection frequency of these two species was almost equal, which shows their balanced role in the occurrence of CFW in Lam Dong. In-planta pathogenicity assays of Fusarium isolates against plantlets grown from cuttings and invitro propagation showed a variation in pathogenicity and a specialisation of isolates for these planting materials. These results suggest that the profiles of population and aggressiveness of Fusarium isolates diverged with the type of planting material, and between the stock and the commercial farms.