Artificial Selection and Pinus radiata

Authors: M.H. Bannister
Publication: New Zealand Journal of Forestry, Volume N.Z.J.For. 1959, Issue N.Z.J.For. 8(1) 1959, pp 69-90, May 1959
Publisher: New Zealand Institute of Forestry

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Abstract: Tree breeders seem to stress too much the size and longevity of their species, and so to forget that trees are plants, and that tree breeding is therefore plant breeding. Breeding methods depend largely on the normal mating system, which is the same in conifers as in many other wind-pollinated species. The method most commonly adopted for breeding conifers has been used for more than thirty years in the breeding of pasture plants. Conifer breeders, therefore, might learn much from a close study of the development of pasture plant breeding, and from a liaison with modern workers in that field.
The variation of important economic characters in Pinus radiata is illustrated by three examples:
(a)   In a random sample of 100 fourteen-year-old trees, the number of cones on the stem varied from 0 to 110.
(b)   In a similar sample, estimates of the basic specific gravity of the juvenile wood ranged from 0.30 to 0.44.
(c)   In a one-parent progeny trial, two progenies showed a highly significant difference in the mean branching frequency of the stem.
Comments on the present policy of artificial selection in P. radiata are:
1.   It may be unwise to select for high branching frequency. This character is merely one of several branch characters, which are interrelated in complex fashion, and which all affect the timber quality.
2.   A selector might place too much emphasis on vegetative vigour, and particularly on height, thus passing over many individuals of high potential for the breeding programme.
3.   Spontaneous selfing within the clones of a seed orchard may cause a wastage of breeding effort. In future, probably greater care will have to be taken to single out individuals which are contemporaneous in their pollination. Another attack on this problem would be to select for self-sterility.
4.   Four isolated local populations of P. radiata are known to exist in the wild state. These are probably all of more or less different genetic composition. Systematic hybridisation between the different provenances might produce valuable results, in terms of new combinations and heterosis.
5.   A wide genetic diversity in P. radiata is desirable, because that is the basis of its adaptability. The wild populations in California may contain many valuable genes which are not present in New Zealand.
* Senior Scientific Officer, Forest Research Institute, Rotorua.
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it might therefore be profitable to collect extensive and representative samples of seed from all the wild populations, and to grow from these a living collection for study and for experimental and practical breeding.
6.   It would be desirable to begin now, in New Zealand, the hybridisation of P. radiata with other species. This work could proceed on a small scale until there was a series of Fi hybrids and others derived from back-crossing to P. radiata. From such small beginnings, interspecific hybridisation might one day assume great importance as a means of imparting a greater ecological amplitude to P. radiata.
Artificial selection in forestry is not solely the prerogative of the tree breeder. Thinning always involves artificial selection; seed collecting should also involve it. These are the responsibilities of the silviculturist, who should never underestimate the power that lies in his own hands for altering the genetic composition of his stands.

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