Genetic gain and diversity under different thinning scenarios in a breeding seed orchard of Quercus accutissima

Abstract

Genetic gain and diversity (status number) were estimated in a 12-year-old Quercus accutissima seedling seed orchard under three thinning scenarios. These scenarios were based on linear (ranged from the removal of individuals within families to the removal of entire families based on the family genetic values generated from conventional progeny test trials), systematic (removal of every second row), and truncation (families with genetic values below the specific threshold value were totally removed) thinning. Both genetic gain and diversity of each scenario were estimated and compared to those of before thinning. Truncation thinning produced the highest genetic gain that was coupled with the lowest diversity, while linear thinning produced the moderate balance between genetic gain and diversity. Systematic thinning, on the other hand, produced the lowest genetic gain and the highest diversity. Under the linear thinning option, the number of family completely removed was minimized to keep up options for further genetic evaluation and selection. This linear thinning was accomplished by applying within family thinning regime that was proportionate to the reverse of every family genetic gain (i.e., low numbers of trees removed from high genetic value families and higher numbers of trees removed from lower genetic value families).