Performance and value of CAD-deficient pine- Final Report

Abstract

The southern US produces 58% of the nation's timber, much of it grown in intensively managed plantations of genetically improved loblolly pine. One of the fastest-growing loblolly pine selections made by the NCSU-Industry Cooperative Tree Improvement Program, whose progeny are widely planted, is also the only known natural carrier of a rare gene, cadn1. This allele codes for deficiency in an enzyme, cinnamyl alcohol dehydrogenase, which catalyzes the last step in the biosynthesis of lignin precursors. This study is to characterize this candidate gene for marker-assisted selection and deployment in the breeding program. This research will enhance the sustainability of forest production in the South, where land-use pressures will limit the total area available in the future for intensively managed plantations. Furthermore, this research will provide information to establish higher-value plantation forests with more desirable wood/fiber quality traits. A rare mutant allele (cad-n1) of the cad gene in loblolly pine (Pinus taeda L.) causes a deficiency in the production of cinnamyl alcohol dehydrogenase (CAD). The effects of this allele were examined by comparing wood density and growth traits of cad-n1 heterozygous trees with those of wild-type trees in a 10-year-old open-pollinated family trial growing under two levels of fertilization in Scotland County, North Carolina. In all, 200 trees were sampled with 100 trees for each treatment. Wood density measurements were collected from wood cores at breast height using x-ray densitometry. We found that the substitution of cad-n1 for a wild-type allele (Cad) was associated with a significant effect on wood density. The cad-n1 heterozygotes had a significantly higher wood density (+2.6%) compared to wild-type trees. The higher density was apparently due to the higher percentage of latewood in the heterozygotes. The fertilization effect was highly significant for both growth and wood density traits. While no cad genotype x treatment interactions was found for any of the traits studied, in the fertilized plots, the effect of the cad-n1 allele on wood density was reduced. The study indicates that the cad-n1 allele could be a valuable gene to the pulp and paper industry for the purpose of enhancing pulp yields through increasing wood density. Stem growth and wood density associated with a mutant null (cad-n1) allele were examined in three 15-year-old loblolly pine diallel tests, established on two sites in the southern United States. In each 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 x 5 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 (p=0.03) years and height growth at ages 6 (p=0.03) and 15 (p=0.005). There were large differences in the cad-n1 effects for the various growth and wood traits among the diallel tests. This variation may be due to either different genetic backgrounds among the parents of the different 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.