Variation in flowering abundance and its impact on the genetic diversity of the seed crop in a Norway spruce seed orchard

The variation in flowering abundance was studied in a Norway spruce seed or chard, located in southern Finland (62 degrees 13'N, 25 degrees 24'E), cons isting of 67 clones from northern Finland (64 degrees -67 degreesN). The fl owering variation in 1984-1996 was studied at the annual, clonal and graft level. In addition, the genetic diversity of an imaginary seed crop was est imated using a concept of status number. The between-year variation was large in both female and male flowering. Dif ferences in flowering abundance among the clones were large and statistical ly significant in all the years studied. The average broad-sense heritabili ty values for female and male flowering were 0.37 and 0.38, respectively, b ut varied considerably from year to year. The correlations between the flow ering abundance of the clones in different years were usually positive and significant. However, the correlations for two pairs of successive good flo wering years showed that the same clones usually Flowered well in the first year in both pairs of years, and the other clones in the second year. The clonal differences in flowering could not be explained by geographic origin , but were more dependent on the graft size. Our results demonstrate that t he variation in the ramet number, flowering abundance and pollen contaminat ion must be included when estimating the genetic diversity of the seed crop in a seed orchard. The relative status number of the seed orchard was 84% of the number of clones when the variation in the ramet number was included . The relative status numbers after adjusting for the variation in female a nd male flowering were on the average 46 and 55%, respectively, and 59% whe n adjusting for both Senders together. Pollen contamination increased the s tatus number considerably.