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Genetic resistance to the white pine weevil in sitka spruce

Author(s) or contact(s): C.C. Ying
Source: Research Branch
Subject: Tree Improvement and Genetics
Series: Research Note
Other details:  Published 1991. Hardcopy is available.


Sitka spruce (Picea sitchensis) accounts for only about 2% of the total coastal reforestation in British Columbia, despite its stumpage price which is the second highest in the province and about twice as high as the average of other species (B.C. Ministry of Forests 1990). Destructive damage caused by the white pine weevil (Pissodes strobi) to plantation Sitka spruce is the major deterrent to reforestation with this species in coastal British Columbia (MacSiurtain 1981; Alfaro 1982, 1989). Planting is now limited to low weevil hazard areas on the Queen Charlotte Islands, North Vancouver Island, and the outer coast of the mid- and north mainland (Heppner and Wood 1984). None of the control techniques, including shading, clipping, insecticides, or biological control, has proved to be sufficiently effective and practical (Cozens 1983). There is increased interest in genetic control, alone and in combination with other control methods, since the discovery of apparent provenance differences in tolerance of weevil attack (Wood 1987). Selection and clonal screening of resistant Sitka spruce has been initiated.

Weevil attack in Sitka spruce provenance trials has been periodically recorded. These results indicated that some of the provenances were able to resist or tolerate weevil attack significantly better than others, suggesting the potential of selecting for weevil resistance. To test this potential, a small scale clonal test was established with grafts in 1984. Early results from this clonal test confirmed what had been observed in the provenance trials. Because of these encouraging results, we have started a program of selecting and screening resistant trees from both provenance plantations and natural stands of resistant provenances. Our goal is to produce operational quantities of resistant trees.

The objective of this report is to provide:
1. a brief overview of the Sitka spruce provenance testing program;
2. a summary of results of weevil attack in provenance and clonal tests;
3. a brief account of progress in the selection and clonal screening of resistant trees; and
4. a discussion on the practical implications of using, selecting, and breeding for genetic resistance in the short and long term. A provenance’s "resistance (tolerance)" or "susceptibility" is defined according to the number of attacks that it experiences over time, or the percent of trees attacked. These terms do not refer to any mechanism of host-insect interaction.

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Updated May 29, 2009