Development of an economic selection index for Australian tea tree
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This study has developed the first formal breeding objective for the Australian tea tree plantation industry. Significant gains in profitability of Australian tea tree (Melaleuca alternifolia) could be made through selection for biomass and oil yield, while maintaining oil quality at acceptable levels. Economic values or weights (EWs), for breeding-objective traits were estimated based on a bio-economic model of a typical production system in Australia. Sensitivity of EWs to the production-system parameters was analysed by what-if scenarios. Selection indices and genetic responses were derived and sensitivity of selection index coefficients to variation in EWs and genetic parameters were analysed by Monte Carlo simulation. The EW for average leaf biomass (LB) and oil content (OC) had the net present value of AU$29.53/kg and AU$2059 per mg/g, respectively. Among the production system parameters studied, discount rate and oil price had large impact on the two EWs, while operating costs changed the EW of LB but did not affect the that of OC. Using optimal selection index, positive expected responses in objective traits LB (36.2 kg/ha/year), OC (4.64 mg/g), and in all selection traits (i.e. juvenile OC, height, leafiness, and 1,8-cineole) were obtained except for terpinen-4-ol, at a 10% selection intensity (i = 1.76). Use of restricted selection index resulted in zero change in either 1,8-cineole or terpinen-4-ol content, but also in an opportunity cost especially in OC. The most important factor affecting the sensitivity of the selection index was the EW for OC.