Bioactive Metabolites from the Fungus Nectria galligena, the Main Apple Canker Agent in Chile

Abstract

The phytopathogenic fungus Nectria galligena Bres. is the most common canker disease agent of hardwood trees. The terpenoids colletochlorin B, colletorin B, ilicicolin C, E, and F, as well as the phytotoxin α,β-dehydrocurvularin have been isolated from liquid cultures of N. galligena obtained from the xylem of infected apple trees in central Chile. Ilicicolin C and F and α,β-dehydrocurvularin were active against Pseudomonas syringae with IC₅₀ values of 28.5, 28.5, and 14.2 μg/mL, respectively, in the same range as streptomycin and penicillin G (11 and 15 μg/mL, respectively). All of the compounds showed moderate inhibitory activity toward the enzymes acetylcholinesterase (AChE) and β-glucuronidase. The most active enzyme inhibitors were colletochlorin B and ilicicolin C and E, with IC₅₀ values of 30−36 μg/mL in the AChE assay and 32−43 μg/mL in the β-glucuronidase test. All of the chlorinated compounds showed some toxicity toward human lung fibroblasts, with IC₅₀ values in the range of 64−120 μg/mL. α,β-Dehydrocurvularin proved to be the most toxic compound, showing IC₅₀ values less than 12 μg/mL. The effect of the isolated compounds on seed germination and radicle and epicotyl growth was assessed in lettuce and millet seeds. At 100 and 200 μg/disk, α,β-dehydrocurvularin significantly reduced radicle length and epicotyl growth in Lactuca sativa. This is the first report on the occurrence of colletochlorin B, colletorin B, ilicicolin C, E, and F, as well as α,β-dehydrocurvularin associated to N. galligena. Keywords: Nectria galligena; Ascomycete; apple canker; colletochlorin B; colletorin B; ilicicolin C, E, and F; α,β-dehydrocurvularin; biological activity