Prediction of genetic gain and gene diversity in seed orchard crops under alternative management strategies

Genetic gain and the gene diversity of seed crops from clonal seed orchards were formulated considering genetic selection, fertility variation and pol len contamination, and compared for five different management strategies. G enetic response was studied as a function of orchard management tactics. Ma nagement variables included the proportion of clones left after genetic thi nning and/or selective seed harvesting. Formulae were derived to calculate gene diversity (expressed as group coancestry or status number) based on th e sex ratio in an orchard population. The influence of having different set s of clones serving as seed parents, or pollen parents, or as both, was ana lysed. In addition, the impact on genetic gain and the gene diversity of se ed crops was studied quantitatively as a function of the quantity and quali ty of gene flow from outside the orchard. The negative impact of fertility variation among orchard genotypes on the gene diversity of the seed crop wa s quantified. Numerical examples were given to illustrate the impact of orc hard management alternatives on genetic gain and gene diversity. The formul ae and results of this study can be used for identifying favourable alterna tives for the management of seed orchards.