OPTIMAL SELECTION INDICES IN EARLY STAGE TRIALS IN SUGARCANE BREEDING PROGRAMS

SELECTION IN SUGARCANE breeding programs is complicated by measured traits being affected greatly by non-genetic effects, especially in early stage selection trials, and because clones vary for multiple traits affecting industry profitability which need to be selected for simultaneously. Selection index theory is a method which accounts for these issues, and has been progressively applied within the Australian sugarcane breeding program. In this paper, the selection index framework is briefly reviewed, and this is used to consider two issues in early stage selection trials. These are (i) adjusting index coefficients for presence of competition effects and genotype × environment interactions and (ii) incorporating traits which have no direct economic impact by themselves (e.g. DNA marker predictions or physiological traits) but which are correlated with other traits of high value (e.g. yield). Hypothetical but realistic examples are given to illustrate the methods. In addition, the economic weighting for fibre is considered. Economic weightings for fibre have recently been reviewed and the impact of different realistic weightings on selection in diverse populations typical of those in early stage trials is considered. Selection indices reflecting value of fibre based on some contrasting prices for electricity were derived and an example set of data presented in this paper. An overall conclusion from analysis of several data sets was that future progress in breeding programs for a range of realistic production systems and assumptions about product prices (e.g. for electricity or biofuel) is unlikely to be sensitive to the relative value of fibre, even at upper ends of likely potential value. Recommendations for dealing with uncertain future fibre values in breeding programs are made.