Variation in the root bark phenolics/sugar ratio of Douglas-fir grown in two plantations in northern Idaho

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Abstract
Several studies have linked high phenolics/sugar ratios in the inner root bark tissue of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) to decreased susceptibility to Armillaria spp. While these studies have identified environmental factors that influence root chemistry, none have examined whether the phenolics/sugar ratio is genetically controlled. In this study, we investigated the effects of genetics and environment on the root bark chemistry of 20 families of 15-year-old Douglas-fir planted in two sites in northern Idaho. Only sugar concentrations varied significantly among families, but site was a significant source of variation for phenolics and the phenolics/sugar ratio. Family × site interactions were significant for the concentrations of all measured root bark compounds as well as for the phenolics/sugar ratio. Phenotypic correlations between height and the phenolics/sugar ratio and between height and sugar concentrations were not significant. However, families with superior height growth and below-average sugar concentrations could be found at both sites. Should a high phenolics/sugar ratio prove effective in selecting genotypes for resistance to Armillaria infection, these results suggest that gains could be made more efficiently by selecting for low sugar concentrations.
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