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Alliance Between Conifer Trees and Endophytic Fungi Against Insect Defoliators

Summary

Researchers discovered that helpful fungi living inside white spruce needles protect the trees from damaging budworm insects. These fungi work in two ways: they directly poison the insects that try to eat the needles, and they also encourage the trees to produce more of their own chemical defenses. This partnership between fungi and trees demonstrates an important co-evolutionary relationship where all three organisms—fungi, trees, and insects—influence each other over time.

Background

Fungal endophytes inhabit plant tissues and can enhance host plant defense against herbivores through direct toxicity or by modulating secondary metabolism. While endophyte-mediated resistance has been studied in annual plants, their role in conifer defenses against insect herbivores remains largely unknown. This study investigates the tripartite interactions among white spruce, endophytic fungi, and the eastern spruce budworm.

Objective

To characterize endophytic fungal communities and terpene concentrations in white spruce families, determine direct and indirect effects of fungal endophytes on eastern spruce budworm, and examine whether changes in fungal communities alter terpene concentrations through inoculation experiments. The study tests a novel Plant Partnership Hypothesis proposing co-evolutionary relationships among fungal endophytes, tree defenses, and insect herbivores.

Results

The study identified 45 endophytic fungal genera with Cladosporium, Tryblidiopsis, Venturia, Lophodermium, and Lirula being most abundant. Fungal endophytes directly reduced budworm fitness through toxic mycelium (100% mortality at high doses) and repellent volatile compounds (70-100% repellency). Inoculation experiments demonstrated that increased fungal abundance corresponded with 28-33% increases in foliar terpene concentrations in seedlings.

Conclusion

Fungal endophytes provide multifaceted anti-herbivory protection to white spruce through both direct toxicity and indirect enhancement of terpene-based chemical defenses. The positive relationship between fungal abundance and terpene production supports the Plant Partnership Hypothesis, demonstrating co-evolutionary relationships among endophytes, plant defenses, and herbivore resistance in conifers.
  • Published in:Plant, Cell & Environment,
  • Study Type:Experimental Research,
  • Source: 10.1111/pce.15503, PMID: 40166909
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