To test for the effects of far‐red light on preventing budset in Picea abies, seedlings of six populations originating from latitudes between 67°N and 47°N were grown for 4–8 weeks in continuous incandescent (metal halogen) light at 300 µmol m−2 s−1 and 20°C and then transferred, at the same temperature, to a daily regime of 8 h incandescent light (300 µmol m−2 s−1) followed by 16 h cool white fluorescent light (40 µmol m−2 s−1). (Cool white lamps are deficient in far‐red light, with a R/FR ratio of 7.5 compared with 2.0 for the incandescent lamps.) All the seedlings from 67° and 80% of those from 64° stopped extension growth and set terminal buds within 28 days of the change of regime. The seedlings from 61° and further south continued growing, as did control seedlings from 67° grown as above but with incandescent light at 20 µmol m−2 s−1 replacing cool white illumination. To distinguish between a clinal and ecotypic pattern of variation, the interval between 64° and 59° was investigated by growing populations originating from that area in the same regimes as before. After 28 days in the cool white day‐extension regime, the percentage budset was 86 for the population from 64°, 0 for the population from 59° and 25–50 for the intermediate populations; i.e. the populations showed a clinal variation in requirement for far‐red light according to latitude. Thus northern populations of Picea abies appear to behave as ‘light‐dominant’ plants for the photoperiodic control of extension growth and budset, whereas the more southern populations behave as ‘dark‐dominant’ plants.

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In Picea abies seedlings the critical night length for bud‐set was determined for provenances from different latitudes, longitudes and altitudes within the natural range of the species. The clinal variation of this character was demonstrated. Inheritance studies indicated that this character is controlled by many genes with predominantly additive effects. In seedlings of Pinus sylvestris and Pinus contorta, growth cessation and bud‐set took place in all light regimes, thus, even under continuous illumination. A photoperiodic optimum for height growth was determined. The photoperiodic influence on such characters as recurrent flushing of shoots, needle growth, dry matter production and frost resistance was demonstrated for northern and southern populations of the two Pinus species. Shorter nights were needed to induce a particular photoperiodic response in the northern populations as compared with those from the south. The importance of reliable phenological characters for assessing frost hardiness in provenance and progeny trials by means of early tests, is discussed.

The existence of strong genetic correlations between traits at an early age and at an adult age should shorten the generation turnover of tree breeding populations and render forest tree breeding more effective. Genetic age-age correlations for tracheid length and wood density were estimated in Scots pine (Pinus sylvestris L.) and the efficiency of early selection for these traits was evaluated. Increment cores of 10-mm diameter were collected from trees of 106 full-sib families in a progeny trial located in southeastern Sweden and consisting of controlled matings between 30 parent trees. The additive genetic age-age correlations were consistently close to unity for all traits and ages studied. The additive genetic variance differed significantly from zero for all traits. The dominance variance was zero for tracheid length and small and insignificant for wood density. The heritabilities varied between 0.3 and 0.5. The genetic gain per year for both tracheid length and wood density was largest if selection was carried out at tree age 11, the lowest age studied, indicating that early tests for these traits will be efficient.

Potential for integration of somatic embryogenesis in a breeding programme of Norway spruce (Picea abies (L.) Karst.), and its limitations, were investigated in a case study with an ordinary breeding population. A standard protocol was used for initiation, proliferation, and cryopreservation of embryogenic cultures; maturation of somatic embryos; and plant regeneration. This is a practical necessity when dealing with a large number of genotypes. Proliferation and maturation were identified as major constraints. Clear differences among families were seen for proliferation and for maturation. For plant regeneration, differences among cell lines within families were considerable while no significant differences were found among families. Significant differences among male parents were obtained for proliferation and maturation. Our calculations show that by using an improved standard protocol, at least one third of the genotypes can be propagated via somatic embryogenesis. No clear relationship was found between embryogenic characters of selected parents based on progenies and corresponding parental breeding values for growth and phenology characters. Three years can be gained by using somatic embryogenesis instead of cuttings in a breeding programme. Maintained propagation ability by including cryopreservation in the breeding programme will provide a very useful link between breeding and mass propagation. The results are encouraging, but further improvement of the standard protocol is necessary.Résumé : Le potentiel et les limites de l'intégration de l'embryogenèse somatique dans un programme d'amélioration génétique de l'épinette de Norvège (Picea abies (L.) Karst.) sont évalués dans une étude de cas d'une population normale de croisements. D'un point de vue pratique, lorsqu'un nombre important de génotypes est considéré, un protocole standard a été utilisé pour l'induction, la maintenance et la cryoconservation des cultures embryogènes, la maturation des embryons somatiques et la régénération en plants. La maintenance et la maturation ont été identifiées comme des contraintes majeures. Des différences claires entre les familles ont été observées pour ces étapes. Pour la régénération en plants, les différences entre lignées cellulaires d'une même famille étaient considérables alors qu'il n'y avait pas de différence significative entre les familles. Des différences significatives entre les parents mâles ont été observées pour la maintenance et la maturation. Nos calculs montrent qu'avec l'utilisation d'un protocole standard amélioré, au moins le tiers des génotypes peut être multiplié par embryogenèse somatique. Aucune relation claire n'a été trouvée entre les caractères embryogènes des parents sélectionnés, basé sur leurs descendances, et les valeurs reproductives correspondantes des parents pour la croissance et les caractères phénologiques. On peut gagner trois ans dans un programme d'amélioration génétique par l'utilisation de l'embryogenèse somatique au lieu du bouturage. Le maintien de la capacité multiplicati...