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Doktorsavhandling, 2023

Diplodia tip blight affecting Scots pine. Factors determining infection and spread in Swedish forests

Brodde, Laura

Sammanfattning

Diplodia sapinea (syn. Sphaeropsis sapinea) is a globally distributed pathogen of conifers. Symptoms of Diplodia tip blight can develop when its host is affected by stressors such as drought, heat or mechanical wounding. This thesis builds on the first detected outbreak of Diplodia tip blight on Scots pine (Pinus sylvestris L.) in Sweden, which marked the northernmost record of such an outbreak of this disease at that time. The aim of this thesis was to generate knowledge about the emergence of Diplodia tip blight. The work showed that the fungus has no apparent restrictions to cause damages on Scots pine in the Nordic climate. Climate, and variation in drought adaptation of pines were potential drivers of the first detected outbreak discovered in 2016. Further, the work showed that D. sapinea is not a recently introduced pathogen in Sweden and is genetically similar to the general European population. Large areas of Scots pine showing severe crown dieback were discovered after the drought of 2018 on Gotland. Diplodia sapinea was associated with the observed symptoms, though not the driver of the dieback. Mortality was highest in severely damaged pines, but pines could recover when the drought stress lessened. Diplodia sapinea was found to be present in healthy-looking stands, trees, and twigs. However, high abundances of D. sapinea were only found in symptomatic twigs of trees showing crown dieback. Endophytic fungal communities depended on health status and these differences were apparent across scales, from tissues to stands. Four species were associated with healthy tree tissue, indicating potential for antagonistic fungi in the endophytic community of Scots pine. A standardized in vitro sporulation method was developed to facilitate future research on the pathosystem D. sapinea – Scots pine. The findings in this thesis contribute knowledge about the range expansion of Diplodia tip blight to the North, and underline the importance of managing stress-related forest pathogens to maintain forest health in the ongoing climate change.

Nyckelord

Diplodia tip blight; Diplodia sapinea; Scots pine; emerging disease,endophyte; drought; fungal community; in vitro sporulation; inoculation assay

Publicerad i

Acta Universitatis Agriculturae Sueciae
2023, nummer: 2023:43
ISBN: 978-91-8046-138-2, eISBN: 978-91-8046-139-9
Utgivare: Swedish University of Agricultural Sciences

    UKÄ forskningsämne

    Forest Science
    Ecology
    Climate Research

    Publikationens identifierare

    DOI: https://doi.org/10.54612/a.49nu5u98e1

    Permanent länk till denna sida (URI)

    https://res.slu.se/id/publ/121958