Aerial branch sampling to detect forest pathogens

Authors: PERROY, RYAN - University Of Hawaii; MEIER, PHILIP - Eth Zurich; COLLIER, ESZTER - University Of Hawaii; HUGHES, MARC - University Of Hawaii; Johnston, Colleen; SULLIVAN, TIMO - Island Conservation; BAUR, THOMAS - Eth Zurich; BUCHMANN, NINA - Eth Zurich; Keith, Lisa

Submitted to: Drones
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/21/2022
Publication Date: 9/24/2022
Citation: Perroy, R.L., Meier, P., Collier, E., Hughes, M., Brill, E., Sullivan, T., Baur, T., Buchmann, N., Keith, L.M. 2022. Aerial branch sampling to detect forest pathogens. Drones. 6(10). Article 275. https://doi.org/10.3390/drones6100275.
DOI: https://doi.org/10.3390/drones6100275

Interpretive Summary: Diagnostic pathogen testing is important for forestry and conservation operations. Eleven symptomatic 'ohi'a (Metrosideros polymorpha) trees on Hawai‘i Island were aerially sampled using Kukuau, a new sUAS attachment for remote aerial tree sampling, and another branch sampling system (the FTTS from ETH Zurich). We tested the samples for Ceratocystis lukuohia, the fungal pathogen responsible for Ceratocystis wilt of ‘ohi'a, a vascular wilt disease which has caused widespread mortality to 'ohi'a in native forests across the state of Hawai‘i. Branch samples were also collected from felled trees inoculated with C. lukuohia, to better characterize the minimum branch diameter needed to successfully detect the pathogen of interest in infected trees. We successfully detected the target fungal pathogen from the collected branches and found that branch diameter, leaf presence and condition, and wood moisture content are important factors in pathogen detection in sampled branches. Results suggest that there is an optimal temporal window for sampling.

Technical Abstract: As sUAS platforms become increasingly capable and integrated into regular forestry and conservation operations, interesting applications exist beyond standard aerial imagery collection. In this work we present the Kukuau branch sampler system, a new sUAS attachment for remote aerial tree sampling that can cut and retrieve branches up to seven cm in diameter for diagnostic pathogen testing and other applications. We aerially sampled 11 symptomatic 'ohi'a (Metrosideros polymorpha) trees on Hawai‘i Island, using Kukuau and another branch sampling system (the FTTS from ETH Zurich), producing 29 branch samples with a maximum diameter of 4.2 cm and length of > 2 m. We tested the samples for Ceratocystis lukuohia, the fungal pathogen responsible for Ceratocystis wilt of ‘ohi'a, a vascular wilt disease which has caused widespread mortality to 'ohi'a in native forests across the state of Hawai‘i. We also tested 63 branch samples (0.8-9.6 cm in diameter) collected from felled trees inoculated with C. lukuohia, to better characterize the minimum branch diameter needed to successfully detect the pathogen of interest in infected trees. We successfully detected the target fungal pathogen from the collected branches and found that branch diameter, leaf presence and condition, and wood moisture content are important factors in pathogen detection in sampled branches. Results indicate that no branches < 1 cm in diameter tested positive for C. lukuohia compared to 77% for branches 5-10 cm in diameter. Inconclusive and/or non-detection laboratory results were obtained from sample materials that were either too desiccated or from a branch with asymptomatic leaves, suggesting there is an optimal temporal window for sampling.