Genetic variation in growth, carbon isotope discrimination, and foliar N concentration in Picea mariana: analyses from a half-diallel mating design using field-grown trees

We performed genetic analyses of growth, carbon isotope discrimination (delta13C), and foliar N concentration using a half-diallel subset of a 7 X 7 complete diallel planted on three sites ranging in water availability. Trees were 22 years old. Heritabilities; general and specific combining abilities; as well as phenotypic, genetic, and environmental correlations were calculated using the best linear unbiased prediction and restricted maximum-likelihood methods. The four traits measured showed variable levels of genetic control. The calculated heritabilities for the traits were as follows: height, 0.39 +/- 0.22 (estimate +/- SD); diameter, 0.14 +/- 0.10; delta13C value, 0.54 +/- 0.26; and foliar N, 0.00. Phenotypic correlations were moderate (r = -0.35), genetic correlations were strong (r = -0.97), and environmental correlations were weak (r = -0.18) between height growth and delta13C. The strong negative genetic correlation between delta13C and growth supports earlier work with a subset of families indicating photosynthetic differences caused genetic variation in delta13C. Inbreeding greatly decreased growth while not impacting delta13C. High heritability, lack of inbreeding depression, and low environmental correlations indicate that a major proportion of delta13C genetic control may be relatively simple. Because delta13C is highly heritable, highly genetically correlated to growth, less environmentally sensitive than growth, and has the possibility of early selection, the trait is a good candidate trait for indirect selection for growth.