Fusarium grosmichelii causes wilt disease on Tibouchina seecandra in China

Tibouchina seecandra is an evergreen shrub, a popular ornamental plant in China. From 2020 to 2021, a wilt disease was observed in T. seecandra in Guangdong province, China. The diseased plants showed typical wilt symptoms including drying out of lower leaves, plant dieback, and total death of the plant. When the diseased stems were sectioned, discolouration of vascular bundles was observed. At the commercial nurseries, the natural disease incidence reached almost 50%, leading to severe economic losses. The putative pathogen was isolated from symptomatic T. seecandra stems. Fusarium grosmichelii was identified as the causal agent by using morphology and molecular phylogeny of multi-loci (DNA-directed RNA polymerase II subunit, translation elongation factor1-alpha, and beta-tubulin) sequence data. Artificial inoculation assays were conducted on potted T. seecandra seedlings under controlled environmental conditions. The results showed that the fungus could produce wilt symptoms in T. seecandra which is similar to those observed in the field. The putative pathogen was re-isolated and Koch's postulates were fulfilled. This study provides the first report of F. grosmichelii causing T. seecandra wilt disease worldwide. Furthermore, these results will contribute to the knowledge of pathogenic Fusarium species on ornamental plants.