Performance of Pinus radiata 'super' seedlings 12 years after outplanting.  I. D. Abbott and L. A. Pederick.  March 1984.  9 pp. (unpubl.)

SUMMARY

Seedlings of outstanding vigour are not uncommon in forest nurseries and have been termed 'super' seedlings. This report describes 12-year results of an experiment initiated to determine whether these trees have genetic potential that could be used in the Pinus radiata D. Don (radiata pine) breeding program.

In June 1971 at Trentham Nursery, 76 seedlings with exceptional height growth were selected, together with an average-sized plant from either side of the select seedlings. The relative height growth of the 'super' seedlings compared with average seedlings ranged from 1.11 to 1.95 for individual plots, when outplanted at Narbethong in row plots of three seedlings per plot.

Twelve years after planting, about 70% of the so-called super trees are still taller than their comparison trees. Though the relative height advantage of the super trees has continued to decline slowly, the difference in mean absolute height has increased, and the relative advantage in diameter has remained stable over the past three years. It appears that the trees may now be exhibiting their real potential and that the super trees, as a class, will continue to be larger. At 12 years, their superiority in height, diameter and volume was 8%, 14% and 40% respectively.

Analyses of form characteristics showed no difference between super trees and comparison trees for straightness, and that super trees had thicker branches, which could be related to the greater vigour of these trees. The lack of any positive advantage in form might have been expected, as the seedlings were selected in the nursery for vigour only.

Although several super trees showed exceptional vigour, the two trees of best form (within a group of seven super trees with volume more than twice the mean for super trees), although straight, would be precluded from selection as plus trees for breeding due to thick branching.

Thus, the selection of super seedlings of radiata pine in the nursery is likely to yield populations of trees with greater than average vigour. The form characteristics of the trees are likely to vary, though on average the trees should be no straighter than the comparison trees and they will tend to have thicker branches. The probability of identifying plus trees for future breeding by following this procedure appears very small.