Pinus thunbergii is an important ornamental species in Taiwan; however, its needles frequently develop yellowish spots that have long been attributed to Lophodermium needle cast. From 2023 to 2025, surveys conducted across 13 sites and 52 sampling events consistently associated these lesions with a slow-growing Basidiomyceteous fungus, identified as Atractidochium hillariae based on morphology and multilocus phylogenetic analyses (ITS, SSU, LSU). Previously reported only as an endophyte of Pinus taeda in the United States, A. hillariae was the dominant fungus isolated from yellowish-spot needles of P. thunbergii, whereas Lophodermium spp. predominated in fallen, dead needles. Detached twig and field inoculations with A. hillariae reproduced restricted bright yellow lesions with reddish-brown centers identical to field symptoms, and the pathogen was successfully reisolated, fulfilling Koch's postulates. The new disease is designated as "Atractidochium needle spot disease". Monthly monitoring revealed that disease severity increased from November, peaked in April-May, and declined in June-July. A newly developed A. hillariae-specific PCR assay targeting the ITS region enabled sensitive (limit of detection, 25 fg μl-1) and specific detection from field samples. In vitro mycelial growth inhibition assays demonstrated that pyraclostrobin and tebuconazole exhibited the strongest inhibition (EC50 -1), suggesting their potential for chemical control. Future research on the disease cycle, host range, and fungicide efficacy in planta will facilitate the development of effective management strategies. It is also worth exploring whether A. hillariae functions as an opportunistic endophyte capable of shifting from a latent to a pathogenic phase under certain conditions.
Huang et al. (2026) studied this question.