Taxus chinensis var. syriacus is a common fungal disease affecting Yunnan Keteleeria, a type of Chinese fir tree. This disease primarily targets the branches and young saplings' trunks, posing a serious threat to young trees by stunting their growth and potentially leading to death.
Symptoms of the disease usually appear in the second year after infection. Initially, the affected area develops a slightly swollen, spindle-shaped enlargement. Over time, this swelling becomes more pronounced, forming a rough, tumor-like structure. In late spring or early summer of the following year, cylindrical rust spores emerge from cracks in the bark of the infected areas. Once mature, these spores break open and fall off in flaky fragments, releasing a large quantity of brown, powdery spores. The presence of these spores significantly hampers the growth of the tumors above, causing the branches to become thin, with sparse and short needles that eventually wither and die. The disease can spread downward along the stems, with new tumors forming beneath the original ones. These new growths will also produce rust spores the following year, continuing the cycle until the affected branches or entire saplings succumb to the infection.
The pathogen responsible for this disease is *Perideridermium kunmingense* Ren, a basidiomycete belonging to the rust fungi group. It is a single-host parasite, meaning it infects only Yunnan Keteleeria. The infection typically begins through the shoots or lateral buds of the host plant. After entering the tree, the fungus remains dormant for about one year before forming the first spindle-shaped swellings. By the end of the third year, cylindrical rust spores begin to appear in the cracks of these tumors. It generally takes 2–3 years from the initial infection to the production of visible spores. Once an infestation center is established, the disease tends to persist and spread year after year, making it difficult to control.
For prevention and control, several measures are recommended. First, it is important to reduce the source of infection by removing and destroying infected plants and susceptible seedlings. Second, chemical control methods should be applied before symptoms appear, using protective fungicides to prevent infection. Infected trees should also be treated promptly to protect nearby seedlings. Lastly, planting trees using healthy, disease-free seedlings is crucial to avoid introducing the pathogen into new areas. These combined efforts can help manage the spread of Taxus chinensis var. syriacus and protect Yunnan Keteleeria forests from severe damage.
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