Diallel crosses in Picea abies IV. Genetic variation and inheritance patterns in short-term trials

The complete diallel cross is the only mating design that provides estimates of variance components of general combining (GCA), specific combining ability (SCA), maternal and reciprocal effects, in addition to heritabilities and genetic correlations. To obtain such estimates, complete diallels were made among 10 trees in each of three natural Norway spruce populations from altitude 300 and 500 m in southern Norway. Seedlings from families from the diallels and open pollinations were tested in short-term tests on agricultural soil at one site at altitude 85 m until age 10 years from seed. Tree height at ages 7 and 10 years and diameter at age 10 had strongly significant GCA variance components within each population. The components for SCA and maternal effects were small and not significant, indicating low levels of non-additive genetic variation. For the days of initiation and cessation of the shoot elongation period the GCA components were dominating and had the highest heritability estimates in two of the diallels. Estimates of genetic correlations between traits measured in earlier nursery trials and height and diameter in the short-term trials had low and not consistent values in the three diallels. The duration of the shoot growth period and rate of growth showed positive relationships with height and diameter. Strong relationships were present between half-sib family means from the diallels and open-pollinated families for height, diameter and phenology traits. Progeny trials testing open-pollinated half-sib families from natural populations can be used for selection of candidates for the initial breeding populations.