First Report of Laurel Wilt Caused by <i>Harringtonia lauricola</i> on Avocado in Taiwan

Although the causal agent of laurel wilt—Harringtonia lauricola—and its principal vector, Xyleborus glabratus, are known to occur naturally in Taiwan (Rablagia et al. 2006; Harrington et al. 2011), the disease itself had not been previously documented in the region. To investigate its presence in avocado (Persea americana), a highly susceptible host, surveys were conducted in July 2025 across ten commercial orchards covering approximately 30 acres. Four orchards—one in Zhusha Township, Xiulin Village, Nantou County, and three in Zhuqi Township, Yihe Village, Chiayi County—had trees exhibiting typical laurel wilt symptoms, including wilting, branch dieback, leaf desiccation, and sapwood streaking. Although signs of ambrosia beetle colonization were visible on affected branches and trunks, no beetles were recovered during sampling. Accurate disease incidence could not be determined, as most symptomatic trees had already been removed or stumped by growers. Sapwood samples from six representative symptomatic trees were excised and cultured on CSMA medium (Navia-Urrutia et al. 2022). All samples consistently yielded isolates morphologically consistent with H. lauricola, characterized by cream-colored colonies with a mucilaginous center and conidiophores grouped in sporodochia. Conidia were hyaline and ovoid, highly variable in size, generally measuring 2.2–8.0 × 1.5–5.5 µm (n = 60). Molecular identification confirmed the pathogen: all isolates (43 in total) tested positive using both conventional PCR with IFW primers (Dreaden et al. 2014; Parra et al. 2020) and LAMP-based β-tubulin primers (Hamilton et al. 2020). LSU sequences obtained from all isolates (PX410286–PX410328) showed 100% identity with the H. lauricola type strain CBS121567. Pathogenicity was assessed by inoculating four replicate seedlings of the avocado cultivar ‘Lula’ with Taiwan isolates AVO-2S-05 and AVO-6S-03, U.S. isolate RL4, and a sterile water control. Inoculations were performed using a spore suspension (10⁶ conidia/plant) following the procedures of Gazis et al. (2022). Plants were monitored for three weeks under controlled conditions (70 °F, 60% relative humidity, 12-hour light/day cycle). All inoculated seedlings developed internal and external symptoms of laurel wilt, while water-inoculated controls remained symptomless. H. lauricola was successfully re-isolated from representative plants in each inoculated group, fulfilling Koch’s postulates. This study marks the first confirmed report of laurel wilt in Taiwan. The disease has caused extensive damage to Florida’s avocado industry and, outside of Florida, has only been documented in Asia in Myanmar (Ploetz et al. 2016). Its detection in Taiwan is especially significant given the country’s emerging avocado industry and underscores the potential threat to avocado-producing regions that overlap with the native distribution of both the pathogen and its vector.