<i>Fusarium</i> and <i>Neocosmospora</i> Species Associated with the Decline of <i>Metasequoia glyptostroboides</i> in China

During surveys conducted in 2020, severe symptoms associated with death and decline were observed on more than 30-year-old <i>Metasequoia glyptostroboides</i> (Chinese redwood) trees in the shelter forests along the Yangtze River in Jingzhou City, Hubei Province, China. A previous study showed that <i>Phytophthora acerina</i> 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 <i>M</i>. <i>glyptostroboides</i> trees. Through morphology and multilocus phylogenetic analysis, these isolates were identified as eight species belonging to the genera <i>Fusarium</i> and <i>Neocosmospora</i>, including <i>F. fujikuroi</i>, <i>F. irregulare</i>, <i>F. odoratissimum</i>, <i>F. reticulatum</i>, <i>N. falciformis</i>, <i>N. keratoplastica</i>, <i>N. solani</i>, and <i>N. tonkinensis</i>. Single inoculation and coinoculation with <i>P. acerina</i> assays of these <i>Fusarium</i> and <i>Neocosmospora</i> species were then performed to test pathogenicity on 3-year-old seedlings of <i>M. glyptostroboides</i>. Lesions (i.e., on seedling stems) caused by species of the genera <i>Neocosmospora</i> and <i>Fusarium</i> were smaller than those caused by <i>P. acerina</i>. Coinoculation of <i>F. fujikuroi</i> and <i>P. acerina</i>, as well as the coinoculation of <i>F. reticulatum</i> and <i>P. acerina</i>, caused larger lesions than inoculation with <i>P. acerina</i> alone. All these species of <i>Fusarium</i> and <i>Neocosmospora</i> were shown to have the potential to be pathogenic to <i>M. glyptostroboides</i>. This study provided evidence that the decline of <i>M. glyptostroboides</i> in Jingzhou is a disease complex.