Growth and form of mountain ash families derived from plus trees and other seed sources.  L. A. Pederick.  May 1988.  20pp. (unpubl.)

SUMMARY

Mountain ash (Eucalyptus regnans) families derived from different categories of parent tree were grown in two progeny trials in the Toolangi forest area in order to study response to selection as judged by diameter growth and straightness. The categories of parent tested included plus trees selected in natural stands (at Toolangi, Neerim, Powelltown and South Gippsland), trees of good phenotype selected on logging coupes (mostly at Powelltown), second generation selections in trials near Powelltown, and some routine seed collections of various origins to act as controls.

The first of the two trials was located at Woodmore Range where 52 families were planted in 10-tree row plots replicated 6 times in 1977, and the other was at Siberia Road where 32 families were planted in 8-tree row plots replicated 7 times in 1979. Both trials were measured when 3 years of age and then again in 1987 when 10 and 8 years old respectively.

At Woodmore, the best families for diameter and straightness were derived from plus trees, and those of local Toolangi origin were better than those of Neerim origin, though that difference only developed after 3 years of age.

At Siberia, the families of plus trees tended to be inferior to those of good phenotypes on logging coupes and the controls, and the Powelltown plus tree families were better than those from Neerim. The best families in the trial were from trees selected on logging coupes in the western part of the Powelltown forest area.

The best families in the trials could not have been predicted on the basis of the phenotype of the parents. Progeny testing therefore appears to be an essential prerequisite to the identification of superior genotypes for breeding when the initial selection is undertaken in the natural forest. Also, a high intensity of selection for rare outstanding plus trees in natural forests may not be efficient because of the environmental variability affecting growth of trees in such areas. Selection of the best trees on logging coupes may be just as successful in locating good genotypes, as was the case in the Siberia trial.

The results have pointed to the existence of provenance differences in the species, but the effects of provenance may have confounded the results through possible genotype x site effects. Thus, at Woodmore, a Toolangi site, the Toolangi families may have been favoured by better adaptation to the local conditions than the other families.

If tree breeding is to be undertaken, particularly in the Toolangi forest area, the best families from Toolangi and Powelltown origins in these trials would provide good genetic material for use in breeding.

Some families from second generation selections grew relatively poorly in the trials but they had been selected at a young age and their growth may have been adversely affected by inbreeding depression.