Association of the cad-n1 allele with increased stem growth and wood density in full-sib families of loblolly pine

Stem growth and wood density associated with a mutant null (cad-n1) allele were examined in three 15-year-old loblolly pine half-diallel tests established on two sites in the southern United States. In each half-diallel test, one or two cad-n1 heterozygous parents were crossed with five unrelated wild-type parents to produce five or ten full-sib families. In all, 839 trees from 20 full-sib families in four genetic backgrounds (a cad-n1 heterozygote × five unrelated trees) were sampled, genotyped at the cad locus, and assessed for growth and wood density traits. In a combined analysis of all four genetic backgrounds, we found evidence for effects of increased wood density associated with the cad-n1 allele at age 15 years (p=0.03) and height growth at ages 6 (p=0.03) and 15 (p=0.005). There were differences in the cad-n1 effects for the various growth and wood traits among the half-diallel tests. This variation may be due to either different genetic backgrounds among the parents of the different half-diallel tests or for different growing environments at the field sites. Even though the cad-n1 effect on growth and wood density was significant across genetic backgrounds, the effect was variable among full-sib families within backgrounds. We speculate that certain wild-type alleles from second parents specifically interact with cad-n1 producing large positive effects. In addition, pleiotropic effects on growth and wood density appear to be associated with the cad-n1 allele. While substantial gains are possible through deployment of trees carrying cad-n1, these gains may be family-specific and should be verified for each cross through field-testing.