Assessment of beech scale resistance in full- and half-sibling American beech families

A beech bark disease infested American beech tree (Fagus grandifolia Ehrh.) and two uninfested trees were selected in a mature natural stand in Michigan, USA, and mated to form two full-sib families for evaluating the inheritance of resistance to beech scale (Cryptococcus fagisuga Lind.), the insect element of beech bark disease. Four half-sib families from both infested and uninfested trees were also evaluated for resistance. Using an artificial infestation technique, adult and egg count data were collected over 2 years and analyzed with generalized linear mixed methods to account for nonnormal distributions of the response variables. A significant effect for family was found for each variable. Family least squares means were computed as a measure of resistance and repeatabilities were calculated to provide an upper limit estimate of broad-sense heritability. The two families that ranked highest for resistance were the full-sib family from two uninfested parents and the half-sib family from a stand where all diseased trees had been removed. Together, the results suggest that selection and breeding may be an effective means to improve populations for artificial regeneration, and silvicultural treatments may provide an effective management option for mitigating beech bark disease through managing the genetic composition of natural regeneration. Resume: Un hetre a grandes feuilles (Fagus grandifolia Ehrh.) infecte par la maladie corticale du hetre et deux hetres sains ont ete selectionnes dans un peuplement naturel mature de l'Etat du Michigan, aux Etats-Unis. Ces arbres ont ete croises pour obtenir deux descendances biparentales dans Ie but d'evaluer Ie caractere hereditaire de la resistance a la cochenille du hetre (Cryptococcus fagisuga Lind.), I'insecte associe ala maladie corticale du hetre. La resistance de quatre descendances uniparentales provenant du hetre infecte et des hetres sains a egalement ete evaluee, AI'aide d'une technique d'infestation artificielle, des donnees de denombrement d'adultes et d'reufs ont ete collectees pendant 2 ans et analysees au moyen de modeles lineaires generalises mixtes pour tenir compte du fait que la distribution des variables de reponse n'etait pas normale. L'effet des descendances etait significatif pour chaque variable. Le moindre carre moyen des descendances a ete calcule en tant que mesure de resistance et la repetabilite a ete calculee pour fournir une estimation de la limite superieure de l'heritabilite au sens large. Les deux descendances qui avaient la plus forte resistance etaient la descendance biparentale provenant des deux parents non infectes et la descendance uniparentale provenant d'un peuplement ou tous les arbres malades avaient ete elimines. Globalement, les resultats indiquent que la selection et l'amelioration genetique peuvent etre des moyens efficaces pour ameliorer les populations pour la regeneration artificielle et que les traitements sylvicoles peuvent fournir une option efficace d'amenagernent pour attenuer l'impact de la maladie corticale du hetre via la gestion de la composition genetique de la regeneration naturelle. [Traduit par la Redaction]