Clonal testing may be the best approach to long-term breeding of Eucalyptus

A computer simulator called breeding cycler has been developed to evaluate a complete cycle in balanced long-term breeding from parents to the next generation parents through testing selection candidates obtained by mating in the breeding population. The efficiency of a breeding program was defined as progress per year at a given annual cost (GMG/Y). Progress was measured as increase in a weighted average of breeding value and gene diversity, thus the loss of gene diversity is considered. Breeding cycler considers three testing strategies for evaluating candidates for the breeding population: Phenotype, Clone and Progeny. Breeding cycler requires a set of inputs, like annual budget, cost components, time components and genetic parameters, which were specified in a main scenario and each parameter was studied over a range with the aim to make the study relevant for much Eucalyptus breeding. Optimal test time and entry size was decided for each testing strategy and the testing strategies were compared. For the main scenario values, the maximum GMG/Y for the Phenotype, Clone and Progeny strategies was 0.42%, 0.636% and 0.331%, respectively. The Clone strategy was superior and the Phenotype strategy was the second best under all input values studied. However, in the case of low heritability, cheap testing and long rotation the differences between Phenotype and Progeny strategies were small. Heritability, additive variance at Mature age, rotation age, plant-dependent cost and time needed to produce the test plants had the strongest effect on GMG/Y. As increase of genotype-depended costs had a small effect on GMG/Y, investments in shortening the time until the females reach fertile age or in improving the success of cloning may pay off. hi conclusion, to achieve the greatest benefit in long-term breeding, the breeding strategy shall primarily be based on clonal testing if this is practically possible, except for high heritability, when Phenotype testing can be the first choice. If cloning is not available, Phenotype strategy could be prefer-able at short rotations and high testing costs. The situation where Progeny testing is most favourable is when the heritability is very low, rotation is greater than 20 years, test plants are cheap to obtain, annual budget is large and flowering is early.