A quantitative framework for breeding and conservation of forest tree genetic resources in British Columbia

Abstract

Over the last decade, forest tree breeders have become aware of the need for gene conservation, but have struggled with methods that would meaningfully integrate breeding and conservation populations. Gene Namkoong has provided the most guidance in this area by defining the role of in- and ex-situ populations in forest tree gene resource management and, particularly, the need for this to be dynamic in time and space. However, once conservation plans for individual species in British Columbia were considered, it became clear that more quantitative structure was needed to provide a framework for attaining practical management objectives. This paper attempts to provide such a framework and show how breeding and conservation populations can be integrated into a continuum of genetic resources. First, capturing only one copy of an allele is likely not satisfactory to meet conservation objectives, and sampling targets should be set higher (e.g., 20) so as to avoid potential problems of inbreeding at later stages in the program. Second, there seems to be a large problem with conserving very low frequency alleles that are recessive, but this occurs in nature as well. Third, in situ populations should be large enough and in a state to persist on their own over several generations, so the more recent effective population size numbers proposed by Lynch (1996) (i.e., ~1000) need to be considered. Fourth, while breeding populations of moderate size (~80) will contain adequate amounts of quantitative genetic variation, they will also contain 20 copies of dominant alleles at frequencies of ~0.20 or higher. Fifth, maintaining and rejuvenating strategic ex-situ test populations now seems to be the only way to conserve low- to mid-frequency alleles that will (i) be reduced in progressive breeding populations by drift and, (ii) over time, not be in desirable genetic backgrounds in in situ populations. Sixth, any reliance on locating mutants in production populations seems generally remote and cannot be relied upon except in a very few situations, although mutation will be important in breeding and in reserves in situ.