Maximizing gain per effort by using clonal replicates in genetic tests.

Models for predicting cummulative genetic gain from recurrent selection applicable to predominantly outcrossing plant species are derived to include the effect of observations on clonal replicates (ramets) in addition to observations on individuals and family means. Such models are discussed with special reference to forest trees. The consequence of redistributing effort from individuals to ramets is investigated for several conditions with a fixed number of families and fixed total test size. Factors that affect the distribution of variance among sources and factors that affect individual selection intensity are the primary determinants of the optimum distribution of effort. The optimum number of ramets ranged from 1 to 6 for the conditions tested and the efficiency of redistribution (ratio of gain for the optimum distribution to the gain for the single-ramet, or non-clonal case) ranged from 1.00 to 1.20. Using clonal replicates in genetic tests usually results in increased cummulative genetic gain relative to non-clonal tests, without an increase in test effort.