Correspondence between single-tree and multiple-tree plot genetic tests for production traits in Pinus sylvestris

Although single-tree plots are often used in genetic tests in tree breeding programmes, it has often been argued that multiple-tree plots can express actual production traits more accurately. Single-tree plots can only be used without objection in genetic tests if they mimic production in closed stands sufficiently well. To determine the degree of this correspondence, genetic correlations between results from single-tree plots and those from multiple-tree plots, expressed as volume per unit area, were estimated for three sets of Scots pine (Pinus sylvestris L.) data, using restricted maximum likelihood methodology with an expectation-maximization algorithm. The number of parents common to the single- and multiple-tree plots varied between 18 and 28 among the different data sets. At the time of measurement the trees were 10-30 years of age. Genetic correlations between height, height increment, diameter, and volume per tree, respectively, in single-tree plots and volume per unit area in multiple-tree plots were strong, with a mean value of approximately 0.8. The results indicate that the performance of single-tree plots corresponds well with production in multiple-tree plots. Comparisons that took the higher selection intensity and lower generation interval into account showed that selection based on height in single-tree plots seemed more efficient than selection based on volume per unit area in multiple-tree plots.