Variation among Norway spruce provenances, families and clones in susceptibility to the spruce gall adelgid ( Adelges abietis )

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Abstract Incidence of the spruce gall adelgid ( Adelges abietis ; “spruce gall aphid” sensu common usage) was assessed as presence/absence in Norway spruce trials in Norway. The trial series comprised a long-term provenance test, a short-term provenance test (36 provenances), three diallel populations (10×10, 10×10, 9×9), a 10×10 factorial cross (100 families), and a clonal test (40 clones). Substantial genetic variation in gall incidence was observed among provenances, among families, and among clones within families. Provenances transferred from low- to mid-elevation Central Europe exhibited higher gall incidence than Nordic and Baltic origins, whereas high-elevation Central European material showed lower incidence. Family-level variation was detected in both natural-population diallels and breeding-population factorial material; a strong agreement was observed between family and derived clone performance (family–clone r ≈ 0.91). Variance-component analyses indicated predominantly additive genetic control, with additional non-additive effects in some crosses. Corresponding narrow-sense heritability estimates were low to moderate (≈ 0.06–0.22). Site effects were evident, with higher expression associated with greater vigor on fertile soils in some trials. Overall, the results indicate that selection for reduced galling is feasible and that provenance choice and site fertility should be considered in deployment and climate-adaptation strategies.

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