Genetic variation in resistance of Norway spruce seedlings to damage by the pine weevil Hylobius abietis

Abstract

Regeneration of northern conifer forests is commonly performed by reforestation with genetically improved materials obtained from long-term breeding programs focused on productivity and timber quality. Sanitary threats can, however, compromise the realization of the expected genetic gain. Including pest resistance traits in the breeding programs may contribute to a sustainable protection. Here we quantified the variation in different components of resistance of Norway spruce to its main pest, the pine weevil Hylobius abietis. We followed insect damage in two large progeny trials (52 openpollinated families with 100-200 individuals per family and trial) naturally infested by the pine weevil. Pine weevils damaged between 17 and 48% of the planted seedlings depending on the trial and year, and mortality due to weevil damage was up to 11.4%. The results indicate significant genetic variation in resistance to the pine weevil, and importantly, the variation was highly consistent across trials irrespective of contrasting incidence levels. Individual heritability estimates for the different components of seedling resistance were consistently low, but family heritabilities were moderate (0.53 to 0.81). While forward selections and breeding for higher resistance seem not feasible, backwards selections of the best parent trees emerge as a putative alternative to reduce weevil damage. A positive genetic correlation between early growth potential and probability of being attacked by the weevil was also observed, but the relationship was weak and appeared only in one of the trials. Overall, results presented here open the door to a new attractive way for reducing damage caused by this harmful pest.

Does the pine weevil (<i>Hylobius abietis</i>) prefer conifer seedlings over other main food sources?

“…These approaches include the selection of more resistant material in breeding programmes (Zas et al 2017) and to enhance the defence of seedlings by methyl jasmonate treatment in the nursery (Zas et al 2014;Fedderwitz et al 2016;Lundborg et al 2016a;Lundborg et al 2016b). Thus, planting regeneration areas with less palatable seedlings should result in less damage occurring to planted seedlings; instead, feeding may be redirected to alternative food sources, such as bark of branches and roots of mature conifer trees, where no economic harm is caused.…”

“…Although pine weevils also feed on roots and branches of mature conifer trees (Eidmann 1974;Örlander et al 2000;Wallertz et al 2006), economic damage is limited to their feeding on planted seedlings; a considerable amount of pine weevil research has therefore focused on their interactions with seedlings (e.g. Fedderwitz et al 2016;Luoranen et al 2017;Zas et al 2017).…”

“…This protective effect, however, tends to disappear in a no-choice situation (Fedderwitz et al 2016). Furthermore, the genetic variation in resistance may be explored to select the more resistant genotypes for planting (Zas et al 2017). The efficiency of these methods is likely to be related to the difference in preference between seedlings and any alternative food resources.…”

Unravelling the functions of biogenic volatiles in boreal and temperate forest ecosystems

“…These include traditional biological control of H. abietis larvae with entomopathogenic nematodes in larval feeding sites in rotten conifer stumps (Kapranas et al 2017). In order to control adult weevils, breeding for resistance (Zas et al 2017), release of repellent BVOCs from dispensers (Lundborg et al 2016b) and treatment with repellent plant extracts (Egigu et al 2011) have been applied. Spraying of natural elicitors such as methyl jasmonate (MeJA), which controls resin acid and MT production, has reduced H. abietis damage intensity in seedlings (Heijari et al 2005;Zas et al 2014;Lundborg et al 2016a, b).…”

Control and Management of the Pine Weevil Hylobius abietis L.

“…For instance, breeding trees for increased resistance against the pine weevil. Genetic variation for the levels of pine weevil damage received by plants has been found for Norway spruce and families with greater resistance have been identified (Zas et al, 2017). Thus, there is future potential for developing resistance breeding program in Norway spruce.…”