A nucleus breeding plan for radiata pine in Australia

The Southern Tree Breeding Association Inc. (STBA), consisting of 20 privat e companies and government agencies working cooperatively to breed improved varieties of radiata pine (Pinus radiata) for Australia, has adopted the c oncept of a nucleus breeding strategy entailing a total breeding population of 300 selections subdivided into two components: a nucleus population (wh ich receives more emphasis in terms of breeding and testing and consists of the best 10% or so of the population) and a main population consisting of the remainder of the breeding population. This paper describes and compares three different plans for operational implementation of a nucleus breeding strategy by the STBA. The first option (Option 1) is the simplest entailin g open-pollinated management of the main population and unified nucleus and main populations. The second two plans (Options 2a and 2b) employ compleme ntary mating designs with pollen-mix management of the main population and a breeding population (consisting of the main and nucleus populations) that is further sub-divided into three unrelated lines. These lines serve as un related breeding groups to manage inbreeding in the deployment population. Options 2a and 2b differ only in the use of seedlings (Option 2a) or rooted cuttings (Option 2b) in unreplicated full-sib family plots used for within -family selection. The three options are compared in terms of costs, logist ics, and detailed genetic gains predictions. In general, costs are similar for all three options and relatively small when compared with the overall S TBA budget. Similarly, all three options are logistically feasible given th e staffing and resources of the STBA. Thus, comparison of genetic gains rep resents the most meaningful criterion for deciding among the three options and in this regard, both Options 2a and 2b are clearly superior to Option 1 . This is largely due to the pollen-mix management of the main population a nd the use of well-replicated progeny tests to estimate GCA. The use of roo ted cuttings in Option 2b adds significantly to the length of the cycle (fr om 12 to 14 years), but also results in more genetic gain per breeding cycl e. An Appendix providing additional details of assumptions and calculations is available from the authors.