Inbreeding Depression in Conifers: Implications for Breeding Strategy
Abstract:Use of selfing as a breeding tool for conifers is controversial; this topic is addressed with a review of genetic models, theory, and experimental results based on a wide range of plants and animals. Some supporting evidence is available from conifer studies. For most conifers, selfing will not be the best method for reducing inbreeding depression in small subpopulations or elite lines of deleterious alleles; sib- or random-mating is a better option in the early generations of conifer domestication. Possible exceptions are conifer species that have few lethal alleles. Few organisms have been studied which have more lethal equivalents than conifers, so slower rates of inbreeding than selfing are needed initially to prevent large losses to low offspring survival and adult fecundity. Inbred breeding populations will also require large numbers of replicate lines and progeny per replicate because the probability of extinction for each line is expected to be high. Like maize, few valuable lines will result from selfing in the initial generations. If inbreeding depression is based on deleterious mutations then it is hypothesized to decline with stringent selection against deleterious alleles (purging). After the initial purging phase, selfingwould be efficient. Advantages of selfing include perfect assortative mating, increased selection efficacy among lines and increased uniformity within lines. Theoretical predictions for inbreeding depression in conifers have outpaced experimentation. Operational breeding programs will not provide needed data on changes in inbreeding depression, but the inbreeding assumptions for breeding strategies must be tested experimentally. We advocate using experimental inbred populations to study direct use of inbreeding depression as a breeding method. It provides first-hand results and lends confidence to long-term population management decisions. The greatest value will be to reveal unforeseen problems, preventing irreversible mistakes. As an example, we outline a plan for a rapidly cycled experimental inbred population for Pinus taeda L. which combines early selection, rapid screening for adult fecundity, and traditional genetic testing. Inbreeding depression research is central to the success of long-term population management. It has become more powerful with integrated classical genetics-molecular approaches, accelerated breeding techniques, and computer simulation models. For. Sci. 42(1):102-117.
Document Type: Journal Article
Affiliations: Department of Genetics, University of Oulu, SF 90570 Oulu Finland
Publication date: 1996-02-01
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