Single- and multiple-trait index selection efficiencies in Fraser fir Christmas trees

Abstract

Selection methods for Abiesfraseri (Pursh) Poir. for Christmas tree wholesale value were evaluated based on parameters from the species' first genetic field test. For single-trait individual selection, combined individual plus family selection at half rotation age (4 years) on total height (HT4) gave the greatest estimated full rotation (8-year) retail value (VALUE) gain of 24.3%. The best 8-year trait, crown diameter, resulted in a gain of only 22.4%. Incorporation of family mean information together with individual values in the selection process was important in maximizing gains. Only 8-year stem straightness (STR8) had unfavorable genetic and phenotypic correlations with other traits. With multitrait combined optimum index selection, use of Kempthorne restrictions to prevent adverse change in this trait seriously limited gains in other 8-year traits. Severity of this limitation increased for younger age indices, and for those with fewer traits. Unrestricted combined optimum indices offered substantial VALUE gain advantages and only small decreases in STR8. Initial selection among seed sources also increased VALUE gain, despite decreasing the effective additive genetic variation. VALUE gains through initial source selection exceeded gain reductions from the genetic variation decreases. The optimum selection strategy, with 30.5% VALUE gain, involved initial source selection followed by unrestricted combined optimum index selection on HT4, and 4-year density. Though slightly below the maximum, this strategy would provide substantial economic and technical advantage in conducting field tests.