Genetic analysis of inbreeding depression in plus tree 850.55 of Pinus radiata D. Don. II. Genetics of viability genes

Most coniferous species exhibit severe inbreeding depression. Selfed indivi duals usually have decreased viability, reduced vigour and morphological de fects. The number of filled seeds after selfing Pinus radiata plus tree 850 .55 was 48% that of the outcrossing and 26.1% of the selfed seedlings died at an early stage. The segregation of 172 markers (covering 56% of the geno me) in selfed progenies of radiata pine plus tree 850.55 was studied. Based on the segregation ratio of the markers, genes associated with inbreeding depression on viability were identified (P < 0.05). Using the Expectation/C onditional Maximization (ECM) algorithm, we estimated the location, degree of dominance and selection coefficient of viability genes. Nine viability g enes were discovered. Seven of them appeared to be dominant and one partial ly dominant (degree of dominance = 0.4). The other gene was overdominant or pseudo-overdominant, with selection coefficients for the two homozygotes o f 0.4 and 0.42, respectively. Of the genes showing dominance or partial dom inance, seven were sub-lethal with selection coefficients ranging from 0.55 to 0.79; one gene (SDPr), which was responsible for seedling death within the first month following germination, was lethal.