Alena Jonsson

A review of the genetics of Betula

The present knowledge on birch genetics is reviewed as regards the fields of cytology, crossability within and between species, flowering, plant growth rhythm, tree growth and quality, and hybridization. Incompatibility occurs but can be partly overcome by crossing at low temperature. Species hybridization was more successful when the female parent was of low ploidy. Crosses within one subsection are not more successful than crosses between subsections. Earliness of male and female flowering can be improved by selection. Flowering is probably polygenically inherited. Clinal variation in north‐south direction occurs for growth rhythm characters, the northern provenances show the earliest growth cessation. Long‐distance transfers northwards or southwards result in reduced growth. The ratio between the family and the population variance components varies with type of character studied and the geographic range of the material studied. Long‐distance crosses within a species or between species do not seem to le...

Genetic variation in nutrient utilization and growth traits in picea abies seedlings

Genetic variation in nitrogen (N) and phosphorus (P) utilization (amount of total biomass produced per unit nutrient in the needles) and growth traits in seedlings from 30 open‐pollinated families of Picea abies (L.) Karst. was estimated. Seedlings were grown under two nutrient regimens: free access to nutrients and restricted access. There was a strong treatment effect on most growth traits. With free access, families allocated relatively more biomass to the stem and less to the roots than they did with restricted access. Heritabilities for growth traits were higher with free access treatment (0.33–0.81) than with restricted access treatment (0.20–0.45). Family variance components for N and P utilization were significant (p < 0.05) with restricted access but not with free access. Genetic correlation between nutrient utilization and height traits with restricted access ranged from none to moderate ( — 0.31 to 0.56). Genetic correlations between the same trait assessed in the two treatments were strong for height and moderate for biomass.

Interfamily variation in nitrogen productivity of pinus sylvestris seedlings

Open‐pollinated families from 21 Pinus sylvestris L. clones from a seed orchard in central Sweden were cultivated in growth chambers in mineral wool for two growth periods. Two nitrogen treatments were applied: high N availability, free access to all nutrient elements and low N availability aimed at 1/3 of the potential requirement under prevailing external conditions. The second treatment was realized by daily additions of nutrient solution containing nitrogen in amounts adjusted to plant size and actual growth rate. Two types of nitrogen productivity were estimated for plants from the low‐N treatment‐one called nitrogen productivity, expressed per day and based only on the period of the intensive growth during the second growth period, the other, called nitrogen productivity per growth period, based on growth increment during the entire second growth period. Nitrogen productivity varied between 7.8 and 10.3 mg plant DW (mg needle‐N)−1 day−1, whereas the nitrogen productivity per growth period varied bet...