Occurrence of Pine Gall Rust on Huangshan Pine Caused by Cronartium orientale in China.

Pine gall rust has emerged as a serious threat to Pinus taiwanensis (Huangshan pine) in Huangshan Mountain, a UNESCO World Heritage site in China. This study systematically investigated the etiology, host range, and epidemiological characteristics of the disease through field surveys, morphological observations, molecular phylogenetic analyses, and inoculation tests. The pathogen was identified as Cronartium orientale based on multi-locus sequencing (SSU, LSU, and ITS) and distinct basidiospore morphology. Quercus stewardii and Castanea seguinii were confirmed as alternate hosts, with Q. stewardii showing higher susceptibility. Microscopic examination revealed detailed spore morphology, and germination assays demonstrated that aeciospores and urediniospores germinate optimally at 12 °C and under near-saturated humidity. Aeciospore dispersal peaked from late April to early May, with spores detected up to 8 m from infected trees, under nearly windless conditions. The life cycle of C. orientale in this region involves annual production of pycnia and aecia on pine, followed by uredinia and telia on alternate hosts, enabling repeated infections. These findings clarify the etiology and epidemiology of pine gall rust on Huangshan pine, providing a scientific basis for disease monitoring and management strategies to protect the ecologically and culturally valuable Huangshan pine forests.