In Vitro Suppression of the Swiss Needle Cast Pathogen <i>Nothophaeocryptopus gaeumannii</i> by Metabolite Extracts from Endophytes of Douglas-Fir

Douglas-fir ( Pseudotsuga menziesii) is one of the most economically important softwood trees grown worldwide. However, the past several decades has seen a decline in its productivity due to increased infection by the fungus Nothophaeocryptopus gaeumannii, the causal agent of Swiss needle cast disease, for which there are currently no feasible control methods. We studied Douglas-fir endophyte extracts to direct future investigations profiling their biologically active natural products. Endophytes were isolated from asymptomatic Douglas-fir needles, and 63 strains representing 32 unique species across 20 families in 14 orders were selected for investigation. A bioassay was developed to assess the antifungal properties of culture filtrate extracts from the endophyte collection against the three distinct N. gaeumannii lineages. Depending on the P value stringency, 26 ( P ≤ 0.05) or 8 ( P ≤ 0.01) strains significantly inhibited the growth of N. gaeumannii, most notably Lachnum virgineum and a putatively novel species of Biscogniauxia. In addition, eight metabolites from the Douglas-fir endophytes Xylaria hypoxylon and Coleophoma sp. were purified and characterized, and an additional 10 metabolites were identified by high-resolution mass spectrometry. Endophytes that inhibited the N. gaeumannii lineages will be prioritized for future studies to determine their potential to modify foliar microbiomes and assist forest disease management. [Formula: see text] Copyright © 2025 His Majesty the King in Right of Canada, as represented by the Minister of Natural Resources Canada. This is an open access article distributed under the CC BY-NC-ND 4.0 International license .