Effects of thinning in progeny tests on estimates of genetic parameters in Pinus radiata

Data from two progeny tests of Pinus radiata were used to examine the effect of thinning on estimates of genetic variances and heritabilities. Each unthinned data set was modified by omitting trees which were subsequently thinned. Heritability estimates for unthinned data were much smaller than for the thinned data. Computer simulated row thinning and selective thinning regimes were also imposed on the otherwise unthinned data sets. Row thinning had no effect but selective thinning produced much higher heritabilities than the unthinned data. The implications of these results and their effects on the way progeny tests are measured are discussed.