Genetic variation in stem deformity of radiata pine on highly fertile sites in north-eastern Victoria.  I. R. Bail and L. A. Pederick.  April 1989.  39pp. (unpubl.)

SUMMARY

The genetic variation in stem deformity of radiata pine (Pinus radiata D.Don) planted on fertile pasture sites in north-eastern Victoria was examined in seven progeny trials aged between 3 and 4 years, one aged 12 years, and a trial of cuttings aged 5 years. The deformities expressed on these sites ranged from slight to extremely severe, and were frequent enough to cause large reductions in timber yield and quality from similarly affected commercial plantations.

The variation was under strong genetic control, with a mean heritability for stem straightness of 0.42. Some families were represented in more than one trial, with similar straightness scores recorded in each. Results of the study are therefore expected to apply generally to other fertile pasture sites. The analysis of three trials designed as disconnected half diallels indicated that the additive component of genetic variance exceeded the non-additive. This means that breeding work based on the general combining ability of the breeding clones should be effective.

Some families previously identified as relatively straight on former native forest sites were quite deformed in these trials, indicating that the stem deformation may be a response to factors that are not present on cleared native forest sites. Strategies for the improvement of planting stock for use on highly fertile sites must therefore be based on selections made on such sites.

Twenty-four of the approximately 340 families that were tested in the trials were found to have a high proportion of straight trees. From their pedigrees, 6 clones that yielded straight offspring were identified. Propagation by seedlings derived from these clones would greatly reduce the frequency of stem deformity on fertile sites. The use of full-sib seedlings of the proven families would increase the gain, but as they are in very limited supply at the moment, large-scale vegetative propagation by cuttings produced from stool plants (hedged seedlings) of the best families is proposed.

Cyclophytic effects demonstrated in one trial indicated that ageing of the stool plants would provide further improvement in stem straightness, and that field-select cuttings are a good short-term option until enough pedigreed stool plants can be brought into production.

Families of Guadalupe Island provenance were superior to Australian radiata pine families for straightness. Cuttings based on crosses among the best Guadalupe trees or between the best Guadalupe and best local clones would be expected to provide trees of particularly good form and growth rate for fertile sites.

A reassessment of a trial at Toorour at age 12 years gave a similar ranking of families to that after an assessment at age 6 years, indicating that an early selection of straight-stemmed families is reliable. In this trial most of the deformation had occurred by age 6 years, providing evidence that the syndrome may be mainly a characteristic of juvenile growth.

Also published:

Bail, I.R. and Pederick, L.A. (1989)  Stem deformity in Pinus radiata on highly fertile sites: expression and genetic variation.  Aust. For. 52: 309-20.