Genetic analysis of inbreeding depression in Pinus radiata d. don

Inbreeding depression is common and severe for conifers. However, little is known about the genes underlying inbreeding depression. This study is to investigate the genes controlling inbreeding depression of viability in plus tree 850.55 of Pinus radiata.; First, a genetic map of Pinus radiata plus tree 850.55 was constructed using megagametophytes of S{dollar}sb1{dollar} seeds. The map contained 19 linkage groups, with 168 RAPD and 4 microsatellite markers. The total map length was 1116.7 cM (Kosambi's function) and was estimated to cover 56% of the genome. Of the 172 markers, 59 (34%) markers were distorted from the expected 1:1 ratio in megagametophytes (P {dollar}<{dollar} 0.05). Segregation distortion due to a single viability gene or sampling error does not affect the estimation of recombination frequency between markers.; Based on the segregation distortion of markers, 9 genes associated with inbreeding depression on viability in plus tree 850.55 were identified. Using the Expectation/Conditional Maximization (ECM) algorithm, the location, degree of dominance and selection coefficient of deleterious genes were estimated. Nine viability genes were discovered. One gene showing overdominance, with selection coefficients for the two homozygotes being 0.4 and 0.42 respectively, was discovered. Seven genes appeared dominant and one partially dominant (degree of dominance = 0.4). Seven viability genes were sub-lethal with selection coefficients of recessive homozygotes ranging from 0.55 to 0.79. One gene (SDPr) was completely lethal, and accounted for all seedling death within one month after germination.; Since inbreeding depression is controlled by many viability genes and most of them are sub-lethal, inbreeding is not a suitable method to purge deleterious alleles from plus tree 850.55. Instead, marker-aided selection can be performed.; This work showed that the effects of polyembryonic selection on segregation are different from those of monoembryonic selection. If selection is of the polyembryonic kind, an excess of lL genotypes (where 1 is a lethal/sublethal allele from the female and L is a normal alternative allele from the male) and a deficit of ll genotypes will occur in the surviving seedlings, but there will be little segregation distortion in the haploid megagametophytes of those seedlings. If selection is only of the monoembryonic kind, then segregation distortion in the seedlings will be limited to deficiencies in the ll genotype, and segregation distortion will be observed in the megagametophytes as well as the germinating seedlings.; For the seven viability genes operating during seed development in tree 850.55, no evidence was found to suggest that polyembryonic selection had taken place. Genetic selection against lethals occurs after a single embryo has survived at random in each seed.