Fungi linked to dying spruce forests in Kyrgyzstan’s mountains

High in the western Tian Shan mountains of Kyrgyzstan, century-old Schrenk’s spruce trees are dying, and researchers have now catalogued the fungal communities living in their diseased roots, stems, and needles. A new study from the Sary-Chelek Biosphere Reserve documents a diverse array of fungi associated with declining Picea schrenkiana trees, revealing distinct tissue-specific patterns of fungal colonization and ruling out one feared culprit: the pine wood nematode responsible for devastating pine wilt disease elsewhere in the world.

The research, conducted by scientists at the Plant Protection Research Centre of the Kyrgyz National Agrarian University, focused on natural stands of Schrenk’s spruce, a dominant conifer in the Western Tian Shan forests. Field surveys conducted in October 2021 and 2022 revealed progressive crown dieback, complete needle loss, bark deterioration, and extensive tree mortality. In the lower stem sections up to roughly half a metre above ground, bark remained moist and firmly attached, while above two metres it was severely desiccated and peeled away easily, exposing the underlying sapwood. Beneath the bark, the researchers found extensive galleries and feeding scars typical of longhorn beetle infestation, along with larval tunnels, frass deposits, and living beetle larvae.

Morphological examination identified all collected longhorn beetles as female Monochamus galloprovincialis, a species notorious as the vector of the pine wood nematode Bursaphelenchus xylophilus in pine wilt disease systems. Because pine wilt disease was a principal concern, the team examined wood samples from symptomatic trees for the nematode. None were detected in any analyzed sample. The researchers also collected specimens of bark beetles and jewel beetles, though immature stages of those families could not be identified to species level. The overall density of insect infestation appeared relatively low, but infested trees consistently showed poor physiological condition and extensive root damage.

To characterize the fungal side of the decline, the team sampled symptomatic tissues including needles, shoots, branches, bark, wood, cones, and fungal fruiting bodies from trees showing needle chlorosis, reddish-brown discoloration, crown dieback, and wood deterioration. Tissue segments cut from the interface between healthy and diseased material were surface-sterilized, plated onto water agar, and incubated until fungal hyphae emerged, typically within five to seven days. Pure cultures were then grown on potato dextrose agar and other media for morphological examination, and genomic DNA was extracted for sequencing of the internal transcribed spacer region of ribosomal RNA, supplemented by the translation elongation factor 1-alpha marker for species-level resolution.

The results revealed striking tissue specificity. Diseased needles harbored the highest fungal diversity, yielding 52 isolates across four genera. Penicillium species accounted for approximately half of the needle community, followed by Alternaria at nearly 30 percent, with Curvularia and Didymella each making up roughly 10 percent. Among the identified species were Penicillium philippinense, Alternaria alternata, Curvularia rouhanii, and Didymella glomerata, each confirmed through both morphological characteristics and ITS sequence analysis. Root tissues yielded 32 isolates dominated by Penicillium, with 25 isolates belonging to that genus and seven to Talaromyces, including Talaromyces domesticus. Stem bark produced 23 isolates, of which 18 were Fusarium, predominantly Fusarium avenaceum alongside Fusarium acuminatum, with the remaining five identified as Trichoderma harzianum.

Several of these associations appear to be newly documented for the region. The isolation of Curvularia rouhanii from symptomatic spruce needles is, according to the authors, among the first records of this species associated with declining Schrenk’s spruce in Central Asia. Talaromyces, likewise, had not previously been reported from Schrenk’s spruce in Kyrgyzstan. The detection of Didymella glomerata, found with characteristic dark pycnidia on infected needles and shoots, expands the known fungal diversity associated with this conifer. The authors caution, however, that the pathogenicity and host range of Curvularia rouhanii in conifer ecosystems remain unresolved, and that pathogenicity experiments and re-isolation studies will be needed to determine whether it can initiate disease or primarily colonizes previously damaged tissue.

The study’s authors are careful to emphasize that the observed fungal diversity should not be interpreted as evidence that all recovered taxa are primary pathogens. Penicillium species are generally regarded as saprotrophs or endophytes, though some can behave as opportunistic pathogens in physiologically weakened or damaged tissues. Their repeated recovery from needles, roots, and stem tissues suggests they may form an important component of the secondary fungal community associated with declining trees, exploiting tissues whose defensive capacity has already been compromised by drought, insect injury, or other environmental stress. Similarly, the association between the longhorn beetle and declining trees does not demonstrate that the insect initiates the decline, and isolation frequency alone cannot distinguish primary pathogens from secondary colonizers.

The absence of both the pine wood nematode and the characteristic fungal associates of the classical pine wilt disease complex, such as Ophiostoma and Ceratocystis species, indicates that the mortality of Schrenk’s spruce in Sary-Chelek follows a different ecological pathway from the well-characterized pine wilt systems of East Asia, Europe, and North America. Instead, the findings support a multifactorial model in which environmental stress, insect activity, host susceptibility, and microbial colonization interact across different stages of tree decline. The researchers note that drought stress has been observed across extensive stands of century-old trees over the past three to five years, with the trend spreading into new areas each year, and that regional climate assessments in Kyrgyzstan identify forest ecosystems as vulnerable sectors requiring improved monitoring and adaptation measures.

Shannon diversity index measurements revealed generally low fungal biodiversity across the studied tree organs throughout the season, with higher values on the needles of diseased trees and consistently low values on roots and trunks. This pattern, the authors suggest, reflects the contrasting microhabitats that different tissues provide in terms of moisture, nutrient availability, chemical composition, and host defense compounds. The compartmentalization of fungal assemblages among needles, roots, and bark may represent different stages and pathways of microbial colonization rather than a uniform community throughout the host, and each fungal species appears to occupy a distinct ecological niche within the forest ecosystem.

The practical implications extend to forest management. The authors recommend that routine forest-health monitoring combine visual assessment of crown condition with surveillance for bark- and wood-boring insects and targeted sampling of symptomatic tissues, noting that sampling needles, roots, and bark separately provides more informative diagnostic data than analyzing bulk plant material. Molecular identification of fungal isolates could establish a regional baseline allowing future surveys to distinguish persistent microbiome components from newly emerging taxa, with particular attention to Curvularia rouhanii, Didymella glomerata, and Talaromyces. The researchers also highlight the potential of native Trichoderma isolates, which frequently occurred in association with Fusarium in bark samples, as candidates for biological control, though any such application would require rigorous assessment of efficacy, host safety, and ecological compatibility. This study provides the first integrated morphological and molecular characterization of fungi associated with declining Schrenk’s spruce in the region, establishing a baseline for future forest health monitoring and conservation programs in the mountain ecosystems of Central Asia.

Subject of Research: Fungal communities associated with diseased Schrenk's spruce trees in Kyrgyzstan

Article Title: Mycobiota associated with diseased Schrenk’s spruce in mountain forest ecosystems of Kyrgyzstan

Article References: Doolotkeldieva, T., & Zhusupova, B. (2026). Mycobiota associated with diseased Schrenk’s spruce in mountain forest ecosystems of Kyrgyzstan. Frontiers in Fungal Biology, 7, Article 1970334. https://doi.org/10.3389/ffunb.2026.1970334

Image Credits: AI Generated

DOI: 10.3389/ffunb.2026.1970334

Keywords: Schrenk's spruce, Picea schrenkiana, forest decline, fungal communities, Kyrgyzstan, Sary-Chelek Biosphere Reserve, Monochamus galloprovincialis, Fusarium, Penicillium, ITS sequencing, forest health, Tian Shan