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Alliance Between Conifer Trees and Endophytic Fungi Against Insect Defoliators

Summary

Tiny fungi living inside white spruce trees help protect them from destructive budworm insects in two ways: the fungi directly produce toxic substances that kill or harm the budworms, and they also trigger the trees to produce more of their own natural chemical defenses called terpenes. Scientists found that spruce trees with more of these helpful fungi in their leaves were better protected against budworm damage. This discovery shows that trees don’t fight pests alone but partner with beneficial fungi as part of their defense system.

Background

Fungal endophytes are microorganisms that inhabit plant tissues without causing harm and can enhance plant defense against herbivores. While endophyte-mediated resistance has been studied in annual plants, their role in conifer defenses against insect herbivores remains largely unknown. This study investigated the co-evolutionary relationships among fungal endophytes, tree defenses, and insect herbivores in white spruce.

Objective

To characterize endophytic fungal communities and terpene concentrations in white spruce families and determine how fungal endophytes contribute to resistance against eastern spruce budworm through direct effects of fungal metabolites and indirect effects on plant secondary metabolism. The study tested the Plant Partnership Hypothesis proposing a co-evolutionary relationship among these three organisms.

Results

Five dominant endophytic fungal genera were identified with variable abundance among families and sites. Fungal endophytes produced secondary metabolites and volatile organic compounds that reduced budworm fitness or induced 100% mortality at higher doses. Inoculation of seedlings with fungal endophytes increased monoterpene and sesquiterpene concentrations by 33% and 28% respectively, with positive correlations between fungal abundance and terpene concentrations.

Conclusion

Fungal endophytes provide direct anti-herbivory protection to eastern spruce budworm through toxic metabolites and volatile compounds, and indirectly enhance plant defense by increasing terpene production. The findings support the Plant Partnership Hypothesis and demonstrate the co-evolutionary importance of endophytic fungi in conifer defenses against insect herbivores.
  • Published in:Plant, Cell & Environment,
  • Study Type:Experimental Research,
  • Source: PMID: 40166909, DOI: 10.1111/pce.15503
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