Clonal differences in planting stock quality of sitka spruce

Abstract Morphological indices of planting stock quality, (shoot: root ratio, sturdiness quotient and Dickson's quality index) were calculated for six clones taken from half sibling families of Picea sitchensis (Bong.) Carr. in Scotland, UK. The clones were grown from stem cuttings and were lifted from the nursery in February. There were significant ( P = 0.05) clonal differences in all morphological indices of quality, and in root length, root tip frequency (number of tips per unit root length) and total number of root tips. By contrast, there was little variation in the number of first-order lateral roots produced per cutting. Significant clonal differences in root growth potential (RGP) were found, which demonstrated the opportunity to select for this important trait. Although plants of the largest clone were twice as heavy as plants from the smallest clone, RGP for these clones differed by a factor of 7. Root growth potential was significantly correlated ( P = 0.05) with the morphological indices of quality, and clones with the largest numbers of root tips had the largest RGP values.