As the use of Valley pine in reforestation increases, so does interest in planting fast-growing stock and ensuring that the most appropriate seed source is used. Research supported by the WVPPCA suggests that the Association is well on its way towards meeting the goal of delivering seed that will produce rapidly-growing, resilient trees.
Natural stands of Valley pine yield a high proportion of inbred seed, as demonstrated by Geoff Gooding (1998 Annual Report). This is significant because trees resulting from inbreeding are more likely to die, especially during stressful conditions, and to be shorter and skinnier than their non-inbred relatives. Indeed, an experiment examining 26-year old ponderosa pine from the eastern Cascade range showed that trees produced by self-pollination were about 2/3 as tall, with ½ the diameter, as those produced by outcross-pollination (Sorenson 1999, see photo).
At present, nearly all Valley pine seedlings available for purchase are grown from seed collected from natural stands, and a proportion are likely to suffer from the effects of inbreeding. Fortunately, the Valley pine seed orchard should produce a crop in the next few years. We expect this seed will be much less inbred, since the seed orchard contains a large number of genetic individuals and will be stimulated to increase pollen production.
A comparison of selfed and
outcrossed ponderosa pine from the eastern
Cascade range growing at a study in Monmouth, OR.
Roguing is anticipated to yield additional improvements in the genetic quality of the orchard seed. The seed orchard was originally planted with six progeny trees per wild, parent tree. For families planted in 1996, the two smallest progeny were recently removed, increasing the average size of the seed orchard and leading to genetic gain. The smallest trees from families planted in 1998 will be cut down based on height data collected this year. Since no families will be eliminated, this increase in genetic quality will be achieved without compromising the genetic diversity of the seed orchard.
The WVPPCA is exploring the feasibility of establishing genetic tests to generate additional genetic gains. Most tree breeding efforts in Oregon have estimated the breeding value (i.e., the vigor and desirability) of wild, parent trees based on the performance of progeny resulting from open- (natural)-pollination. This approach cannot be used for Valley Pine since the growth and vigor of progeny will reflect both the breeding value of the parents and the level of inbreeding. Instead, control-pollinations must be performed. Such breeding will not be feasible until the seed orchard begins to produce a consistent cone crop.
Citation: Sorenson, F. C. 1999. Relationship between self-fertility, allocation of growth, and inbreeding depression in three coniferous species. Evolution 53: 417-425.