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

Rafael Zas,Bo Karlsson,Stefan Jansson,Luis Sampedro,Claes Hellqvist,Niklas Björklund,Göran Nordlander

doi:10.1007/s11295-017-1193-1

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 open-pollinated 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.

Highlights

Regeneration of northern conifer forests in Europe and America is increasingly performed by means of reforestation with genetically improved material on areas previously opened by clear-cuts (Nilsson et al 2010)
We explored the genetic variation in the susceptibility to the insect among open pollinated families selected from the Norway spruce breeding population of southern Sweden, analyzing the incidence of the insect in two progeny trials naturally infested by the pest
The results indicate significant genetic variation in resistance to the pine weevil, and importantly, the variation was highly consistent across trials irrespective of contrasting weevil incidence levels

Summary

Introduction

Regeneration of northern conifer forests in Europe and America is increasingly performed by means of reforestation with genetically improved material on areas previously opened by clear-cuts (Nilsson et al 2010). After decades of intensive selection, testing, and breeding in long-term breeding programs, high-quality genetic materials with superior volume growth and wood properties are available and massively used for forest regeneration (Lindgren et al 2008). Compromise the realization of the expected genetic gain. One of these sanitary threats is the pine weevil Hylobius abietis (L.), which can cause extremely high mortality rates during the first years after planting in recent clear-cuts (Långström and Day 2004). In order to maintain survival rates at acceptable levels, 111 Page 2 of 12

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