Fusarium and Neocosmospora Species Associated with the Decline of Metasequoia glyptostroboides in China

During surveys conducted in 2020, severe symptoms associated with death and decline were observed on >30-year-old Metasequoia glyptostroboides (Chinese redwood) trees in the shelter-forests along Yangtze River in Jingzhou city, Hubei province, China. A previous study showed that Phytophthora acerina was one of the causal agents of the decline of the Chinese redwood. In this study, a total of 147 fungal isolates were obtained from the diseased roots and xylem of trunks of declining M. glyptostroboides trees. Through morphology and multi-locus phylogenetic analysis, these isolates were identified as eight species belonging to the genera Fusarium and Neocosmospora including F. fujikuroi, F. irregulare, F. odoratissimum, F. reticulatum， N. falciformis, N. keratoplastica, N. solani, and N. tonkinensis. Single inoculation and co-inoculation with P. acerina assays of these Fusarium and Neocosmospora species were then performed to test pathogenicity on three-year-old seedlings of M. glyptostroboides. Lesions (i.e., on seedling stems) caused by species of the genera Neocosmopora and Fusarium were smaller than those caused by P. acerina. Co-inoculation of F. fujikuroi and P. acerina, as well as the co-inoculation of F. reticulatum and P. acerina caused larger lesions than inoculations with P. acerina alone. All these species of Fusarium and Neocosmospora were shown to have the potential to be pathogenic to M. glyptostroboides. This study provided evidence that the decline of M. glyptostroboides in Jingzhou is a disease complex.