Lammas shoots in Norway spruce families in short-term trials; genetic variation, inheritance patterns and implications of micro-environmental influence

This study presents information about the variability between and within populations of Norway spruce in lammas shoot formation. Assessments of lammas shoots were conducted in two short-term trials involving full sib families of Norway spruce from two complete diallel crosses, each originating from a natural population. These assessments were made over two growing seasons when the trees were six and seven years from seed, during which early summer temperatures varied significantly. The trees were grown on former agricultural land with large variation in soil fertility across the field. The proportion of trees with lammas shoots varied among blocks, ranging from 1 to 14 %, with the highest values in the blocks with the most fertile soil conditions. A substantial variation was also found among families from each population regarding the percentage of trees with lammas shoots, varying among half-sib families from 2 to 20 % and 1 to 19 % in the two populations, respectively. The largest part of this genetic variation was additive, with high values for the general combining ability (GCA) variance components and low values of the specific combining ability (SCA), maternal and reciprocal components. Estimates of narrow sense heritability were 0.40 for transformed lammas shoot scores in both diallels. Generally, families with an early start and early cessation of shoot elongation had the highest frequency of lammas shoots. In one of the diallels, families with a high lammas shoot percentage also had the highest number of ramicorn branches in a field trial at age 12 and 26 years from seed.