Optimal Clone Number for Seed Orchards with Tested Clones

Abstract

The optimal number of clones in seed orchards is discussed. A model is constructed to maximize a goodness criterion (“benefit”) for seed orchards. This criterion is a function of: 1) the number of tested genotypes available for selection and planted in seed orchard; 2) the contribution to pollination from: a) the ramet itself; b) the closest neighbors; c) the rest of the orchard and sources outside the orchard (contamination); 3) variation among genotypes for fertility; 4) frequency of selfing; 5) production of selfed genotypes; 6) gene diversity (= status number); 7) influence of contamination; 8) genetic variation among candidates; 9) correlation between selection criterion (e.g. height in progeny test) and value for forestry (e.g. production in forests from the orchard); and 10) the number of clones harvested. Numeric values of the entries are discussed, and values were chosen to be relevant for scenarios with Swedish conifers (focusing on Scots pine) and for loblolly pine. Benefit was maximized considering the number of clones. The optimum was 16 clones for the Swedish scenario, while less for the loblolly pine scenario. The optimum was rather broad, thus it is not essential to deploy the exact optimum, and an approximate optimum will do. A sensitivity analyses was performed to evaluate the importance of the likely uncertainty and variation in different entries. Quantification of the benefit of gene diversity is important. Other significant considerations are the genetic variance in the goal character and the ability to predict it, as well as the impact of selfing and the variation in reproductive success between clones. Twenty clones is suggested as a thumb rule for Swedish conifers.

Mating dynamics of Scots pine in isolation tents

“…The latter value is derived from the presumption that N e of 10 secures capturing of 95 % of the genetic diversity existing in the base population (Nei 1973;Yanchuk 2001). According to Lindgren and Prescher (2005), the optimum N e for Scots pine is 16.…”

Gain and diversity in advanced generation coastal Douglas-fir selections for seed production populations

“…Many studies on tree breeding theory considered the effects of selection on gain estimates and genetic diversity in the form of an effective population size for breeding and production populations (Wei andLindgren 1995, 1996;Lindgren and Mullin 1997;Andersson et al 1999;Kang 2001;Olsson et al 2001, Lindgren andPrescher 2005). Although these studies stress the trade-offs between diversity and genetic gain that follow selection decisions, they do not consider explicitly the biological cost of inbreeding in terms of the merchantable volume production at rotation age.…”

Genetic diversity and forest reproductive material - from seed source selection to planting

“…A distinction should be made when discussing the number of clones in seed orchards and in clonal forestry (Lindgren & Prescher 2005). Therefore, in this section we will address to the number of clones or genotypes in plantations and deal with structure of seed orchards later.…”

“…In Sweden, Finland and Korea the usual number of clones in conifers SO ranges from 70 to 139 (Kang et al 2001), while in the USA 24 clones (14-36) are usually considered for Pinus taeda L. and 42 (25-55) for Pinus elliottii Engelm (McKeand et al 2003). For the establishment of SO in Finland the minimum number of clones is 30 (Koski 1980) and in Sweden the proposed number is 20 clones (Lindgren & Prescher 2005). Concerning the number of clones to include in the establishment of SO, different recommendations are made by a number of authors: more than 20 clones (Johnson & Lipow 2002), no more than 30 (Yanchuk et al 2006) or 40 (Bishir & Roberds 1999), between 30 to 40 (Roberds & Bishir 1997), more than 40 (Koski 2000).…”